run sequential   # run stressors sequentially
verbose          # verbose output
metrics-brief    # show metrics at end of run
timeout 60s      # stop each stressor after 60 seconds
#
# vm stressor options:
#
vm 2             # 2 vm stressors
vm-bytes 128M    # 128 MB available memory shared by 2 vm stressors
vm-keep          # keep vm mapping
vm-populate      # populate memory
#
# memcpy stressor options:
#
memcpy 5         # 5 memcpy stressors

The job file introduces the run command that specifies how to run the stressors:

run sequential - run stressors sequentially
run parallel - run stressors together in parallel

Note that 'run parallel' is the default.

The following columns of information are output:

--access N

start N workers that work through various settings of file mode bits (read, write, execute) for the file owner and checks if the user permissions of the file using access(2) and faccessat(2) are sane.

--access-ops N

stop access workers after N bogo access sanity checks.

--acl N

start N workers that exercise permutations of ACL access permission settings on user, group and other tags.

--acl-rand

randomize (by shuffling) the order of the ACL access permissions before exercising ACLs.

--acl-ops N

stop acl workers after N bogo acl settings have been set.

--affinity N

start N workers that run 16 processes that rapidly change CPU affinity (for systems that provide sched_setaffinity()). Rapidly switching CPU affinity can contribute to poor cache behaviour and high context switch rate.

--affinity-delay N

delay for N nanoseconds before changing affinity to the next CPU. The delay will spin on CPU scheduling yield operations for N nanoseconds before the process is moved to another CPU. The default is 0 nanosconds.

--affinity-ops N

stop affinity workers after N bogo affinity operations.

--affinity-pin

pin all the 16 per stressor processes to a CPU. All 16 processes follow the CPU chosen by the main parent stressor, forcing heavy per CPU loading.

--affinity-rand

switch CPU affinity randomly rather than the default of sequentially.

--affinity-sleep N

sleep for N nanoseconds before changing affinity to the next CPU.

--af-alg N

start N workers that exercise the AF_ALG socket domain by hashing and encrypting various sized random messages. This exercises the available hashes, ciphers, rng and aead crypto engines in the Linux kernel.

--af-alg-dump

dump the internal list representing cryptographic algorithms parsed from the /proc/crypto file to standard output (stdout).

--af-alg-ops N

stop af-alg workers after N AF_ALG messages are hashed.

--aio N

start N workers that issue multiple small asynchronous I/O writes and reads on a relatively small temporary file using the POSIX aio interface. This will just hit the file system cache and soak up a lot of user and kernel time in issuing and handling I/O requests. By default, each worker process will handle 16 concurrent I/O requests.

--aio-ops N

stop POSIX asynchronous I/O workers after N bogo asynchronous I/O requests.

--aio-requests N

specify the number of POSIX asynchronous I/O requests each worker should issue, the default is 16; 1 to 4096 are allowed.

--aiol N

start N workers that issue multiple 4 K random asynchronous I/O writes using the Linux aio system calls io_setup(2), io_submit(2), io_getevents(2) and io_destroy(2). By default, each worker process will handle 16 concurrent I/O requests.

--aiol-ops N

stop Linux asynchronous I/O workers after N bogo asynchronous I/O requests.

--aiol-requests N

specify the number of Linux asynchronous I/O requests each worker should issue, the default is 16; 1 to 4096 are allowed.

--alarm N

start N workers that exercise alarm(2) with MAXINT, 0 and random alarm and sleep delays that get prematurely interrupted. Before each alarm is scheduled any previous pending alarms are cancelled with zero second alarm calls.

--alarm-ops N

stop after N alarm bogo operations.

--apparmor N

start N workers that exercise various parts of the AppArmor interface. Currently one needs root permission to run this particular test. Only available on Linux systems with AppArmor support and requires the CAP_MAC_ADMIN capability.

--apparmor-ops

stop the AppArmor workers after N bogo operations.

--atomic N

start N workers that exercise various GCC __atomic_*() built in operations on 8, 16, 32 and 64 bit integers that are shared among the N workers. This stressor is only available for builds using GCC 4.7.4 or higher. The stressor forces many front end cache stalls and cache references. Note that 32 bit systems do not currently exercise 64 bit integers.

--atomic-ops N

stop the atomic workers after N bogo atomic operations.

--bad-altstack N

start N workers that create broken alternative signal stacks for SIGSEGV and SIGBUS handling that in turn create secondary SIGSEGV/SIGBUS errors. A variety of randonly selected nefarious methods are used to create the stacks:

--bad-altstack-ops N

stop the bad alternative stack stressors after N SIGSEGV bogo operations.

--bad-ioctl N

start N workers that perform a range of illegal bad read ioctls (using _IOR) across the device drivers. This exercises page size, 64 bit, 32 bit, 16 bit and 8 bit reads as well as NULL addresses, non-readable pages and PROT_NONE mapped pages. Currently only for Linux and requires the --pathological option.

--bad-ioctl-method [ inc | random | random-inc | stride ]

select the method of changing the ioctl command (number, type) tuple per iteration, the default is random-inc. Available bad-ioctl methods are described as follows:

Method	Description
inc	increment ioctl command by 1
random	use a random ioctl command
random-inc	increment ioctl command by a random value
random-stride	increment ioctl command number by 1 and decrement command type by 3

--bad-ioctl-ops N

stop the bad ioctl stressors after N bogo ioctl operations.

--besselmath N

start N workers that exercise various Bessel functions. Results are sanity checked to ensure no variation occurs after each round of 10000 computations.

--besselmath-ops N

stop after N bessel bogo-operation loops.

--besselmath-method method

specify a Bessel function to exercise. Available bessel stress methods are described as follows:

Method	Description
all	iterate over all the below Bessel functions methods
j0	double precision Bessel function of the first kind of order 0
j1	double precision Bessel function of the first kind of order 1
jn	double precision Bessel function of the first kind of order n (where n = 5 for this test)
j0f	float precision Bessel function of the first kind of order 0
j1f	float precision Bessel function of the first kind of order 1
jnf	float precision Bessel function of the first kind of order n (where n = 5 for this test)
j0l	long double precision Bessel function of the first kind of order 0
j1l	long double precision Bessel function of the first kind of order 1
jnl	long double precision Bessel function of the first kind of order n (where n = 5 for this test)
y0	double precision Bessel function of the second kind of order 0
y1	youble precision Bessel function of the second kind of order 1
yn	double precision Bessel function of the second kind of order n (where n = 5 for this test)
y0f	float precision Bessel function of the second kind of order 0
y1f	float precision Bessel function of the second kind of order 1
ynf	float precision Bessel function of the second kind of order n (where n = 5 for this test)
y0l	long double precision Bessel function of the second kind of order 0
y1l	long double precision Bessel function of the second kind of order 1
ynl	long double precision Bessel function of the second kind of order n (where n = 5 for this test)

-B N, --bigheap N

start N workers that grow their heaps by reallocating memory. If the out of memory killer (OOM) on Linux kills the worker or the allocation fails then the allocating process starts all over again. Note that the OOM adjustment for the worker is set so that the OOM killer will treat these workers as the first candidate processes to kill.

--bigheap-bytes N

maximum heap growth as N bytes per bigheap worker. One can specify the size as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--bigheap-growth N

specify amount of memory to grow heap by per iteration. Size can be from 4 K to 64 MB. Default is 64 K.

--bigheap-mlock

attempt to mlock future allocated pages into memory causing more memory pressure. If mlock(MCL_FUTURE) is implemented then this will stop newly allocated pages from being swapped out.

--bigheap-ops N

stop the big heap workers after N bogo allocation operations are completed.

--binderfs N

start N workers that mount, exercise and unmount binderfs. The binder control device is exercised with 256 sequential BINDER_CTL_ADD ioctl calls per loop.

--binderfs-ops N

stop after N binderfs cycles.

--bind-mount N

start N workers that repeatedly bind mount / to / inside a user namespace. This can consume resources rapidly, forcing out of memory situations. Do not use this stressor unless you want to risk hanging your machine.

--bind-mount-ops N

stop after N bind mount bogo operations.

--bitonicsort N

start N workers that sort 32 bit integers using bitonic sort.

--bitonicsort-ops N

stop bitonic sort stress workers after N bogo bitonic sorts.

--bitonicsort-size N

specify number of 32 bit integers to sort, default is 262144 (256 × 1024).

--bitops N

start N workers that perform various calculations using 32 bit integer manipulation operations. Many of these are derived from the Standford "Bit Twiddling Hacks" (Sean Eron Anderson) and Hacker's Delight (Henry S. Warren, Jr.)

--bitops-ops N

stop after N bitop operations.

--bitops-method method

specify bitops stress method. By default, all the bitops stress methods are exercised sequentially, however one can specify just one method to be used if required. Available bitops stress methods are described as follows:

Method	Description
all	iterate over all the below bitops stress methods.
abs	calculate the absolute value of a 32 bit signed integer. Computed two different ways, one with masking and addition, one with masking and subtraction.
countbits	count the number of bits set to 1 in a 32 bit unsigned integer. Computed five different ways, two with bit counting, one with 64 bit multiplication, one with parallelised masking and shifting, one using a builtin popcount function.
clz	count the number of leading zero bits in a 32 bit unsigned integer. Computed four different ways, one with bit counting, one with log2 shifting, one using a builtin popcount function, one using a builtin clz function,
ctz	count the number of trailing zero bits in a 32 bit unsigned integer. Computed five different ways, one with bit cointing, one using masking and shifting, one using the masking and ternary operator Gaudet method, one using a builtin clz function, one using a builtin popcount function.
cmp	compare two 32 bit unsigned integers with comparison results of -1, 0, 1 for less than, equal or greater than. Computed 3 ways, one using simple comparisons, two using comparisons and subtraction.
log2	calculate log base 2 of a 32 bit unsigned integer. Computed four ways, one using bit counting, one using masking and shifting and braching, one using masking and shifting with no branching, one using shifting and bitwise or'ing.
max	find the maximum of two 32 bit unsigned integers without a temporary variable. Computed two ways, one using xor'ing and masking, one using the ternary operator.
min	find the minimum of two 32 bit unsigned integers without a temporary variable. Computed two ways, one using xor'ing and masking, one using the ternary operator.
parity	compute the parity of a 32 bit unsigned integer. Computed five ways, two using bit counting, one using multiplication, shifting and xor'ing, one using shifting and xor'ing, one using a builtin parity function.
rnddnpwr2	find the nearest power of 2 of a 32 bit unsigned integer, rounded down. Computed three ways, one using bit counting and shifting, one using shifting and or'ing, one using a shift and the builtin ctz function.
rnduppwr2	find the nearest power of 2 of a 32 bit unsigned integer, rounded up. Computed three ways, one using bit counting and shifting, one using shifting and or'ing, one using a shift and the builtin ctz function.
reverse	reverse the bits of a 32 bit unsigned integer. Computed six ways, one using bit shifting loop, one using bit shitting and mask loop, one using parallelised masking and shifting, one using 64 bit multiplication, one using 32 bit multiplication, one using the builtin bitreverse32 function.
sign	calculate the sign of a 32 bit signed integer. Computed two ways, one using a branchless less than zero operator, one using sign bit shifting and negation.
swap	swap two 32 bit signed integers without a temporary variable. Computed two ways, one using subtraction and addition, one using xor'ing.

--branch N

start N workers that randomly branch to 1024 randomly selected locations and hence exercise the CPU branch prediction logic.

--branch-ops N

stop the branch stressors after N × 1024 branches

--brk N

start N workers that grow the data segment by one page at a time using multiple brk(2) calls. Each successfully allocated new page is touched to ensure it is resident in memory. If an out of memory condition occurs then the test will reset the data segment to the point before it started and repeat the data segment resizing over again. The process adjusts the out of memory setting so that it may be killed by the out of memory (OOM) killer before other processes. If it is killed by the OOM killer then it will be automatically re-started by a monitoring parent process.

--brk-bytes N

maximum brk growth as N bytes per brk worker. One can specify the size as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--brk-mlock

attempt to mlock future brk pages into memory causing more memory pressure. If mlock(MCL_FUTURE) is implemented then this will stop new brk pages from being swapped out.

--brk-notouch

do not touch each newly allocated data segment page. This disables the default of touching each newly allocated page and hence avoids the kernel from necessarily backing the page with physical memory.

--brk-ops N

stop the brk workers after N bogo brk operations.

--bsearch N

start N workers that binary search a sorted array of 32 bit integers using bsearch(3). By default, there are 65536 elements in the array. This is a useful method to exercise random access of memory and processor cache.

--bsearch-method [ bsearch-libc | bsearch-nonlibc | ternary ]

select either the libc implementation of bsearch or a slightly optimized non-libc implementation of bsearch or a 3-day ternary search. The default is the libc implementation if it exists, otherwise the non-libc version.

--bsearch-ops N

stop the bsearch worker after N bogo bsearch operations are completed.

--bsearch-size N

specify the size (number of 32 bit integers) in the array to bsearch. Size can be from 1 K to 4 M.

--bubblesort N

start N workers that sort 32 bit integers using bubblesort.

--bubblesort-method [ bubblesort-fast | bubblesort-naive ]

select either a standard optimized implementation of bubblesort or a naive unoptimized implementation of bubblesort. The default is the standard optimized version.

--bubblesort-ops N

stop bubblesort stress workers after N bogo bubblesorts.

--bubblesort-size N

specify number of 32 bit integers to sort, default is 16384.

-C N, --cache N

start N workers that perform random wide spread memory read and writes to thrash the CPU cache. The code does not intelligently determine the CPU cache configuration and so it may be sub-optimal in producing hit-miss read/write activity for some processors. Note: to exercise cache misses it is recommended to instead use the matrix-3d stessor using the --matrix-3d-zyx option.

--cache-cldemote

cache line demote (x86 only). This is a no-op for non-x86 architectures and older x86 processors that do not support this feature.

--cache-clflushopt

use optimized cache line flush (x86 only). This is a no-op for non-x86 architectures and older x86 processors that do not support this feature.

--cache-clwb

cache line writeback (x86 only). This is a no-op for non-x86 architectures and older x86 processors that do not support this feature.

--cache-enable-all

where appropriate exercise the cache using cldemote, clflushopt, fence, flush, sfence and prefetch.

--cache-fence

force write serialization on each store operation (x86 only). This is a no-op for non-x86 architectures.

--cache-flush

force flush cache on each store operation (x86 only). This is a no-op for non-x86 architectures.

--cache-level N

specify level of cache to exercise (1=L1 cache, 2=L2 cache, 3=L3/LLC cache (the default)). If the cache hierarchy cannot be determined, built-in defaults will apply.

--cache-no-affinity

do not change processor affinity when --cache is in effect.

--cache-ops N

stop cache thrash workers after N bogo cache thrash operations.

--cache-prefetch

force read prefetch on next read address on architectures that support prefetching.

--cache-sfence

force write serialization on each store operation using the sfence instruction (x86 only). This is a no-op for non-x86 architectures.

--cache-size N

override the default cache size setting to N bytes. One can specify the in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--cache-ways N

specify the number of cache ways to exercise. This allows a subset of the overall cache size to be exercised.

--cacheline N

start N workers that exercise reading and writing individual bytes in a shared buffer that is the size of a cache line. Each stressor has 2 running processes that exercise just two bytes that are next to each other. The intent is to try and trigger cacheline corruption, stalls and misses with shared memory accesses. For an N byte sized cacheline, it is recommended to run N / 2 stressor instances.

--cacheline-affinity

frequently change CPU affinity, spread cacheline processes evenly across all online CPUs to try and maximize lower-level cache activity. Attempts to keep adjacent cachelines being exercised by adjacent CPUs.

--cacheline-method method

specify a cacheline stress method. By default, all the stress methods are exercised sequentially, however one can specify just one method to be used if required. Available cacheline stress methods are described as follows:

Method	Description
all	iterate over all the below cpu stress methods.
adjacent	increment a specific byte in a cacheline and read the adjacent byte, check for corruption every 7 increments.
atomicinc	atomically increment a specific byte in a cacheline and check for corruption every 7 increments.
bits	write and read back shifted bit patterns into specific byte in a cacheline and check for corruption.
copy	copy an adjacent byte to a specific byte in a cacheline.
inc	increment and read back a specific byte in a cacheline and check for corruption every 7 increments.
mix	perform a mix of increment, left and right rotates a specific byte in a cacheline and check for corruption.
rdfwd64	increment a specific byte in a cacheline and then read in forward direction an entire cacheline using 64 bit reads.
rdints	increment a specific byte in a cacheline and then read data at that byte location in naturally aligned locations integer values of size 8, 16, 32, 64 and 128 bits.
rdrev64	increment a specific byte in a cacheline and then read in reverse direction an entire cacheline using 64 bit reads.
rdwr	read and write the same 8 bit value into a specific byte in a cacheline and check for corruption.

--cacheline-ops N

stop cacheline workers after N loops of the byte exercising in a cacheline.

--cap N

start N workers that read per process capabilities via calls to capget(2) (Linux only).

--cap-ops N

stop after N cap bogo operations.

--cgroup N

start N workers that mount a cgroup, move a child to the cgroup, read, write and remove the child from the cgroup and umount the cgroup per bogo-op iteration. This uses cgroup v2 and is only available for Linux systems.

--cgroup-ops N

stop after N cgroup bogo operations.

--chattr N

start N workers that attempt to exercise file attributes via the EXT2_IOC_SETFLAGS ioctl. This is intended to be intentionally racy and exercise a range of chattr attributes by enabling and disabling them on a file shared amongst the N chattr stressor processes. (Linux only).

--chattr-ops N

stop after N chattr bogo operations.

--chdir N

start N workers that change directory between directories using chdir(2).

--chdir-dirs N

exercise chdir on N directories. The default is 8192 directories, this allows 64 to 65536 directories to be used instead.

--chdir-ops N

stop after N chdir bogo operations.

--chmod N

start N workers that change the file mode bits via chmod(2) and fchmod(2) on the same file. The greater the value for N then the more contention on the single file. The stressor will work through all the combination of mode bits.

--chmod-ops N

stop after N chmod bogo operations.

--chown N

start N workers that exercise chown(2) on the same file. The greater the value for N then the more contention on the single file.

--chown-ops N

stop the chown workers after N bogo chown(2) operations.

--chroot N

start N workers that exercise chroot(2) on various valid and invalid chroot paths. Only available on Linux systems and requires the CAP_SYS_ADMIN capability.

--chroot-ops N

stop the chroot workers after N bogo chroot(2) operations.

--clock N

start N workers exercising clocks and POSIX timers. For all known clock types this will exercise clock_getres(2), clock_gettime(2) and clock_nanosleep(2). For all known timers it will create a random duration timer and busy poll this until it expires. This stressor will cause frequent context switching.

--clock-ops N

stop clock stress workers after N bogo operations.

--clone N

start N workers that create clones (via the clone(2) and clone3() system calls). This will rapidly try to create a default of 8192 clones that immediately die and wait in a zombie state until they are reaped. Once the maximum number of clones is reached (or clone fails because one has reached the maximum allowed) the oldest clone thread is reaped and a new clone is then created in a first-in first-out manner, and then repeated. A random clone flag is selected for each clone to try to exercise different clone operations. The clone stressor is a Linux only option.

--clone-max N

try to create as many as N clone threads. This may not be reached if the system limit is less than N.

--clone-ops N

stop clone stress workers after N bogo clone operations.

--close N

start N workers that try to force race conditions on closing opened file descriptors. These file descriptors have been opened in various ways to try and exercise different kernel close handlers.

--close-ops N

stop close workers after N bogo close operations.

--context N

start N workers that run three threads that use swapcontext(3) to implement the thread-to-thread context switching. This exercises rapid process context saving and restoring and is bandwidth limited by register and memory save and restore rates.

--context-ops N

stop context workers after N bogo context switches. In this stressor, 1 bogo op is equivalent to 1000 swapcontext calls.

--copy-file N

start N stressors that copy a file using the Linux copy_file_range(2) system call. 128 KB chunks of data are copied from random locations from one file to random locations to a destination file. By default, the files are 256 MB in size. Data is sync'd to the filesystem after each copy_file_range(2) call.

--copy-file-bytes N

copy file size, the default is 256 MB. One can specify the size as % of free space on the file system or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--copy-file-ops N

stop after N copy_file_range() calls.

-c N, --cpu N

start N workers exercising the CPU by sequentially working through all the different CPU stress methods. Instead of exercising all the CPU stress methods, one can specify a specific CPU stress method with the --cpu-method option.

-l P, --cpu-load P

load CPU with P percent loading for the CPU stress workers. 0 is effectively a sleep (no load) and 100 is full loading. The loading loop is broken into compute time (load%) and sleep time (100% - load%). Accuracy depends on the overall load of the processor and the responsiveness of the scheduler, so the actual load may be different from the desired load. Note that the number of bogo CPU operations may not be linearly scaled with the load as some systems employ CPU frequency scaling and so heavier loads produce an increased CPU frequency and greater CPU bogo operations.

Note: This option only applies to the --cpu stressor option and not to all of the cpu class of stressors.

--cpu-load-slice S

note: this option is only useful when --cpu-load is less than 100%. The CPU load is broken into multiple busy and idle cycles. Use this option to specify the duration of a busy time slice. A negative value for S specifies the number of iterations to run before idling the CPU (e.g. -30 invokes 30 iterations of a CPU stress loop). A zero value selects a random busy time between 0 and 0.5 seconds. A positive value for S specifies the number of milliseconds to run before idling the CPU (e.g. 100 keeps the CPU busy for 0.1 seconds). Specifying small values for S lends to small time slices and smoother scheduling. Setting --cpu-load as a relatively low value and --cpu-load-slice to be large will cycle the CPU between long idle and busy cycles and exercise different CPU frequencies. The thermal range of the CPU is also cycled, so this is a good mechanism to exercise the scheduler, frequency scaling and passive/active thermal cooling mechanisms.

Note: This option only applies to the --cpu stressor option and not to all of the cpu class of stressors.

--cpu-method method

specify a cpu stress method. By default, all the stress methods are exercised sequentially, however one can specify just one method to be used if required. Available cpu stress methods are described as follows:

Method	Description
all	iterate over all the below cpu stress methods
ackermann	Ackermann function: compute A(3, 7), where: A(m, n) = n + 1 if m = 0; A(m - 1, 1) if m > 0 and n = 0; A(m - 1, A(m, n - 1)) if m > 0 and n > 0 For other recursive methods, refer to the hanoi cpu stress method.
apery	calculate Apery's constant ζ(3); the sum of 1/(n ↑ 3) to a precision of 1.0x10↑14
bitops	various bit operations from bithack, namely: reverse bits, parity check, bit count, round to nearest power of 2
callfunc	recursively call 8 argument C function to a depth of 1024 calls and unwind
cfloat	1000 iterations of a mix of floating point complex operations
cdouble	1000 iterations of a mix of double floating point complex operations
clongdouble	1000 iterations of a mix of long double floating point complex operations
collatz	compute the 1348 steps in the collatz sequence starting from number 989345275647. Where f(n) = n / 2 (for even n) and f(n) = 3n + 1 (for odd n).
correlate	perform a 8192 × 512 correlation of random doubles
crc16	compute 1024 rounds of CCITT CRC16 on random data
decimal32	1000 iterations of a mix of 32 bit decimal floating point operations (GCC only)
decimal64	1000 iterations of a mix of 64 bit decimal floating point operations (GCC only)
decimal128	1000 iterations of a mix of 128 bit decimal floating point operations (GCC only)
dither	Floyd-Steinberg dithering of a 1024 × 768 random image from 8 bits down to 1 bit of depth
div8	50,000 8 bit unsigned integer divisions
div16	50,000 16 bit unsigned integer divisions
div32	50,000 32 bit unsigned integer divisions
div64	50,000 64 bit unsigned integer divisions
div128	50,000 128 bit unsigned integer divisions
double	1000 iterations of a mix of double precision floating point operations
euler	compute e using n = (1 + (1 ÷ n)) ↑ n
explog	iterate on n = exp(log(n) ÷ 1.00002)
factorial	find factorials from 1..150 using Stirling's and Ramanujan's approximations
fibonacci	compute Fibonacci sequence of 0, 1, 1, 2, 5, 8...
fft	4096 sample Fast Fourier Transform
fletcher16	1024 rounds of a naïve implementation of a 16 bit Fletcher's checksum
float	1000 iterations of a mix of floating point operations
float16	1000 iterations of a mix of 16 bit floating point operations
float32	1000 iterations of a mix of 32 bit floating point operations
float64	1000 iterations of a mix of 64 bit floating point operations
float80	1000 iterations of a mix of 80 bit floating point operations
float128	1000 iterations of a mix of 128 bit floating point operations
floatconversion	perform 65536 iterations of floating point conversions between float, double and long double floating point variables.
gamma	calculate the Euler-Mascheroni constant γ using the limiting difference between the harmonic series (1 + 1/2 + 1/3 + 1/4 + 1/5 ... + 1/n) and the natural logarithm ln(n), for n = 80000.
gcd	compute GCD of integers
gray	calculate binary to gray code and gray code back to binary for integers from 0 to 65535
hamming	compute Hamming H(8,4) codes on 262144 lots of 4 bit data. This turns 4 bit data into 8 bit Hamming code containing 4 parity bits. For data bits d1..d4, parity bits are computed as: p1 = d2 + d3 + d4 p2 = d1 + d3 + d4 p3 = d1 + d2 + d4 p4 = d1 + d2 + d3
hanoi	solve a 21 disc Towers of Hanoi stack using the recursive solution. For other recursive methods, refer to the ackermann cpu stress method.
hyperbolic	compute sinh(θ) × cosh(θ) + sinh(2θ) + cosh(3θ) for float, double and long double hyperbolic sine and cosine functions where θ = 0 to 2π in 1500 steps
idct	8 × 8 IDCT (Inverse Discrete Cosine Transform).
int8	1000 iterations of a mix of 8 bit integer operations.
int16	1000 iterations of a mix of 16 bit integer operations.
int32	1000 iterations of a mix of 32 bit integer operations.
int64	1000 iterations of a mix of 64 bit integer operations.
int128	1000 iterations of a mix of 128 bit integer operations (GCC only).
int32float	1000 iterations of a mix of 32 bit integer and floating point operations.
int32double	1000 iterations of a mix of 32 bit integer and double precision floating point operations.
int32longdouble	1000 iterations of a mix of 32 bit integer and long double precision floating point operations.
int64float	1000 iterations of a mix of 64 bit integer and floating point operations.
int64double	1000 iterations of a mix of 64 bit integer and double precision floating point operations.
int64longdouble	1000 iterations of a mix of 64 bit integer and long double precision floating point operations.
int128float	1000 iterations of a mix of 128 bit integer and floating point operations (GCC only).
int128double	1000 iterations of a mix of 128 bit integer and double precision floating point operations (GCC only).
int128longdouble	1000 iterations of a mix of 128 bit integer and long double precision floating point operations (GCC only).
int128decimal32	1000 iterations of a mix of 128 bit integer and 32 bit decimal floating point operations (GCC only).
int128decimal64	1000 iterations of a mix of 128 bit integer and 64 bit decimal floating point operations (GCC only).
int128decimal128	1000 iterations of a mix of 128 bit integer and 128 bit decimal floating point operations (GCC only).
intconversion	perform 65536 iterations of integer conversions between int16, int32 and int64 variables.
ipv4checksum	compute 1024 rounds of the 16 bit ones' complement IPv4 checksum.
jmp	Simple unoptimised compare >, <, == and jmp branching.
lfsr32	16384 iterations of a 32 bit Galois linear feedback shift register using the polynomial x↑32 + x↑31 + x↑29 + x + 1. This generates a ring of 2↑32 - 1 unique values (all 32 bit values except for 0).
ln2	compute ln(2) based on series: 1 - 1/2 + 1/3 - 1/4 + 1/5 - 1/6 ...
logmap	16384 iterations computing chaotic double precision values using the logistic map Χn+1 = r × Χn × (1 - Χn) where r > ≈ 3.56994567
longdouble	1000 iterations of a mix of long double precision floating point operations.
loop	simple empty loop.
matrixprod	matrix product of two 128 × 128 matrices of double floats. Testing on 64 bit x86 hardware shows that this is provides a good mix of memory, cache and floating point operations and is probably the best CPU method to use to make a CPU run hot.
nsqrt	compute sqrt() of long doubles using Newton-Raphson.
omega	compute the omega constant defined by Ωe↑Ω = 1 using efficient iteration of Ωn+1 = (1 + Ωn) / (1 + e↑Ωn).
parity	compute parity using various methods from the Standford Bit Twiddling Hacks. Methods employed are: the naïve way, the naïve way with the Brian Kernigan bit counting optimisation, the multiply way, the parallel way, the lookup table ways (2 variations) and using the __builtin_parity function.
phi	compute the Golden Ratio ϕ using series.
pi	compute π using the Srinivasa Ramanujan fast convergence algorithm.
prime	find the first 10000 prime numbers using a slightly optimised brute force naïve trial division search.
psi	compute ψ (the reciprocal Fibonacci constant) using the sum of the reciprocals of the Fibonacci numbers.
queens	compute all the solutions of the classic 8 queens problem for board sizes 1..11.
rand	16384 iterations of rand(), where rand is the MWC pseudo random number generator. The MWC random function concatenates two 16 bit multiply-with-carry generators: x(n) = 36969 × x(n - 1) + carry, y(n) = 18000 × y(n - 1) + carry mod 2 ↑ 16 and has period of around 2 ↑ 60.
rand48	16384 iterations of drand48(3) and lrand48(3).
rgb	convert RGB to YUV and back to RGB (CCIR 601).
sieve	find the first 10000 prime numbers using the sieve of Eratosthenes.
stats	calculate minimum, maximum, arithmetic mean, geometric mean, harmoninc mean and standard deviation on 250 randomly generated positive double precision values.
sqrt	compute sqrt(rand()), where rand is the MWC pseudo random number generator.
trig	compute sin(θ) × cos(θ) + sin(2θ) + cos(3θ) for float, double and long double sine and cosine functions where θ = 0 to 2π in 1500 steps.
union	perform integer arithmetic on a mix of bit fields in a C union. This exercises how well the compiler and CPU can perform integer bit field loads and stores.
zeta	compute the Riemann Zeta function ζ(s) for s = 2.0..10.0

--cpu-old-metrics

as of version V0.14.02 the cpu stressor now normalizes each of the cpu stressor method bogo-op counters to try and ensure a similar bogo-op rate for all the methods to avoid the shorter running (and faster) methods from skewing the bogo-op rates when using the default "all" method. This is based on a reference Intel i5-8350U processor and hence the bogo-ops normalizing factors will be skew somewhat on different CPUs, but so significantly as the original bogo-op counter rates. To disable the normalization and fall back to the original metrics, use this option.

--cpu-ops N

stop cpu stress workers after N bogo operations.

--cpu-online N

start N workers that put randomly selected CPUs offline and online. This Linux only stressor requires root privilege to perform this action. By default the first CPU (CPU 0) is never offlined as this has been found to be problematic on some systems and can result in a shutdown.

--cpu-online-affinity

move the stressor worker to the CPU that will be next offlined.

--cpu-online-all

The default is to never offline the first CPU. This option will offline and online all the CPUs including CPU 0. This may cause some systems to shutdown.

--cpu-online-ops N

stop after offline/online operations.

--cpu-sched N

start N workers that exercise the scheduler by moving processes to different CPUs. Each worker starts 16 child processes and repeatedly moves the processes to different CPUs and attempts changes their scheduler policy using SCHED_OTHER, SCHED_BATCH, SCHED_IDLE, SCHED_EXT, SCHED_DEADLINE, SCHED_RR and SCHED_FIFO policies. The choice of CPU placement is based on 8 different mechanisms and is changed every second to mix process placements on all the available CPUS. The child processes are run with randomizied nice settings to exercise scheduler prioritization.

--cpu-sched-ops N

stop after N child process move attempts.

--crypt N

start N workers that encrypt a 16 character random password using crypt(3). The password is encrypted using MD5, NT, SHA-1, SHA-256, SHA-512, scrypt, SunMD5 and yescrypt encryption methods.

--crypt-method method

select the encryption method, may be one of: all, MD5, NT, SHA-1, SHA-256, SHA-512, scrypt, SunMD5 or yescrypt. The 'all' method selects all the methods and is the default.

--crypt-ops N

stop after N bogo encryption operations.

--cyclic N

start N workers that exercise the real time FIFO or Round Robin schedulers with cyclic nanosecond sleeps. Normally one would just use 1 worker instance with this stressor to get reliable statistics. By default this stressor measures the first 10 thousand latencies and calculates the mean, mode, minimum, maximum latencies along with various latency percentiles for the just the first cyclic stressor instance. One has to run this stressor with CAP_SYS_NICE capability to enable the real time scheduling policies. The FIFO scheduling policy is the default.

--cyclic-dist N

calculate and print a latency distribution with the interval of N nanoseconds. This is helpful to see where the latencies are clustering.

--cyclic-method [ clock_ns | itimer | poll | posix_ns | pselect | usleep ]

specify the cyclic method to be used, the default is clock_ns. The available cyclic methods are as follows:

Method	Description
clock_ns	sleep for the specified time using the clock_nanosleep(2) high resolution nanosleep and the CLOCK_REALTIME real time clock.
itimer	wakeup a paused process with a CLOCK_REALTIME itimer signal.
poll	delay for the specified time using a poll delay loop that checks for time changes using clock_gettime(2) on the CLOCK_REALTIME clock.
posix_ns	sleep for the specified time using the POSIX nanosleep(2) high resolution nanosleep.
pselect	sleep for the specified time using pselect(2) with null file descriptors.
usleep	sleep to the nearest microsecond using usleep(2).

--cyclic-ops N

stop after N sleeps.

--cyclic-policy [ deadline | fifo | rr ]

specify the desired real time scheduling policy, deadline, fifo (first-in, first-out) or rr (round-robin).

--cyclic-prio P

specify the scheduling priority P. Range from 1 (lowest) to 100 (highest).

--cyclic-samples N

measure N samples. Range from 1 to 100000000 samples.

--cyclic-sleep N

sleep for N nanoseconds per test cycle using clock_nanosleep(2) with the CLOCK_REALTIME timer. Range from 1 to 1000000000 nanoseconds.

--daemon N

start N workers that each create a daemon that dies immediately after creating another daemon and so on. This effectively works through the process table with short lived processes that do not have a parent and are waited for by init. This puts pressure on init to do rapid child reaping. The daemon processes perform the usual mix of calls to turn into typical UNIX daemons, so this artificially mimics very heavy daemon system stress.

--daemon-ops N

stop daemon workers after N daemons have been created.

--daemon-wait

wait for daemon child processes rather than let init handle the waiting. Enabling this option will reduce the daemon fork rate because of the synchronous wait delays.

--dccp N

start N workers that send and receive data using the Datagram Congestion Control Protocol (DCCP) (RFC4340). This involves a pair of client/server processes performing rapid connect, send and receives and disconnects on the local host.

--dccp-domain D

specify the domain to use, the default is ipv4. Currently ipv4 and ipv6 are supported.

--dccp-if NAME

use network interface NAME. If the interface NAME does not exist, is not up or does not support the domain then the loopback (lo) interface is used as the default.

--dccp-msgs N

send N messages per connect, send/receive, disconnect iteration. The default is 10000 messages. If N is too small then the rate is throttled back by the overhead of dccp socket connect and disconnects.

--dccp-port P

start DCCP at port P. For N dccp worker processes, ports P to P - 1 are used.

--dccp-ops N

stop dccp stress workers after N bogo operations.

--dccp-opts [ send | sendmsg | sendmmsg ]

by default, messages are sent using send(2). This option allows one to specify the sending method using send(2), sendmsg(2) or sendmmsg(2). Note that sendmmsg is only available for Linux systems that support this system call.

--dekker N

start N workers that exercises mutex exclusion between two processes using shared memory with the Dekker Algorithm. Where possible this uses memory fencing and falls back to using GCC __sync_synchronize if they are not available. The stressors contain simple mutex and memory coherency sanity checks.

--dekker-ops N

stop dekker workers after N mutex operations.

-D N, --dentry N

start N workers that create and remove directory entries. This should create file system meta data activity. The directory entry names are suffixed by a gray-code encoded number to try to mix up the hashing of the namespace.

--dentry-ops N

stop denty thrash workers after N bogo dentry operations.

--dentry-order [ forward | reverse | stride | random ]

specify unlink order of dentries, can be one of forward, reverse, stride or random. By default, dentries are unlinked in random order. The forward order will unlink them from first to last, reverse order will unlink them from last to first, stride order will unlink them by stepping around order in a quasi-random pattern and random order will randomly select one of forward, reverse or stride orders.

--dentries N

create N dentries per dentry thrashing loop, default is 2048.

--dev N

start N workers that exercise the /dev devices. Each worker runs 5 concurrent threads that perform open(2), fstat(2), lseek(2), poll(2), fcntl(2), mmap(2), munmap(2), fsync(2) and close(2) on each device. Note that watchdog devices are not exercised.

--dev-file filename

specify the device file to exercise, for example, /dev/null. By default the stressor will work through all the device files it can fine, however, this option allows a single device file to be exercised.

--dev-ops N

stop dev workers after N bogo device exercising operations.

--dev-shm N

start N workers that fallocate large files in /dev/shm and then mmap these into memory and touch all the pages. This exercises pages being moved to/from the buffer cache. Linux only.

--dev-shm-ops N

stop after N bogo allocation and mmap /dev/shm operations.

--dfp N

start N workers that exercise addition, multiplication and division operations on a range of decimal floating point types. For each type, 8 floating point values are operated upon 65536 times in a loop per bogo op.

--dfp-method method

select the decimal floating point method to use, available methods are:

Method	Description
all	iterate over all the following floating point methods:
df32add	32 bit decimal floating point add (_Decimal32)
df64add	64 bit decimal floating point add (_Decimal64)
df128add	128 bit decimal floating point add (_Decimal128)
df32mul	32 bit decimal floating point multiply (_Decimal32)
df64mul	64 bit decimal floating point multiply (_Decimal64)
df128mul	128 bit decimal floating point multiply (_Decimal128)
df32div	32 bit decimal floating point divide (_Decimal32)
df64div	64 bit decimal floating point divide (_Decimal64)
df128div	128 bit decimal floating point divide (_Decimal128)

--dfp-ops N

stop after N decimal floating point bogo ops.

--dir N

start N workers that create, rename and remove directories using mkdir, rename and rmdir.

--dir-dirs N

exercise dir on N directories. The default is 8192 directories, this allows 64 to 65536 directories to be used instead.

--dir-ops N

stop directory thrash workers after N bogo directory operations.

--dirdeep N

start N workers that create a depth-first tree of directories to a maximum depth as limited by PATH_MAX or ENAMETOOLONG (which ever occurs first). By default, each level of the tree contains one directory, but this can be increased to a maximum of 10 sub-trees using the --dirdeep-dir option. To stress inode creation, a symlink and a hardlink to a file at the root of the tree is created in each level.

--dirdeep-bytes N

allocated file size, the default is 0. One can specify the size as % of free space on the file system or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g. Used in conjunction with the --dirdeep-files option.

--dirdeep-dirs N

create N directories at each tree level. The default is just 1 but can be increased to a maximum of 36 per level.

--dirdeep-files N

create N files at each tree level. The default is 0 with the file size specified by the --dirdeep-bytes option.

--dirdeep-inodes N

consume up to N inodes per dirdeep stressor while creating directories and links. The value N can be the number of inodes or a percentage of the total available free inodes on the filesystem being used.

--dirdeep-ops N

stop directory depth workers after N bogo directory operations.

--dirmany N

start N stressors that create as many files in a directory as possible and then remove them. The file creation phase stops when an error occurs (for example, out of inodes, too many files, quota reached, etc.) and then the files are removed. This cycles until the run time is reached or the file creation count bogo-ops metric is reached. This is a much faster and light weight directory exercising stressor compared to the dentry stressor.

--dirmany-bytes N

allocated file size, the default is 0. One can specify the size as % of free space on the file system or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--dirmany-ops N

stop dirmany stressors after N empty files have been created.

--dnotify N

start N workers performing file system activities such as making/deleting files/directories, renaming files, etc. to stress exercise the various dnotify events (Linux only).

--dnotify-ops N

stop inotify stress workers after N dnotify bogo operations.

--dup N

start N workers that perform dup(2) and then close(2) operations on /dev/zero. The maximum opens at one time is system defined, so the test will run up to this maximum, or 65536 open file descriptors, which ever comes first.

--dup-ops N

stop the dup stress workers after N bogo open operations.

--dynlib N

start N workers that dynamically load and unload various shared libraries. This exercises memory mapping and dynamic code loading and symbol lookups. See dlopen(3) for more details of this mechanism.

--dynlib-ops N

stop workers after N bogo load/unload cycles.

--eigen N

start N workers that exercise the Eigen C++ matrix library for 2D matrix addition, multiplication, determinant, inverse and transpose operations on long double, double and float matrices. This currently is only available for gcc/g++ builds.

--eigen-method method

select the floating point method to use, available methods are:

Method	Description
all	iterate over all the Eigen 2D matrix operations
add-longdouble	addition of two matrices of long double floating point values
add-double	addition of two matrices of double floating point values
add-float	addition of two matrices of floating point values
determinant-longdouble	determinant of matrix of long double floating point values
determinant-double	determinant of matrix of double floating point values
determinant-float	determinant of matrix of floating point values
inverse-longdouble	inverse of matrix of long double floating point values
inverse-double	inverse of matrix of double floating point values
inverse-float	inverse of matrix of floating point values
multiply-longdouble	mutiplication of two matrices of long double floating point values
multiply-doublee	mutiplication of two matrices of double floating point values
multiply-float	mutiplication of two matrices of floating point values
transpose-longdouble	transpose of matrix of long double floating point values
transpose-double	transpose of matrix of double floating point values
transpose-float	transpose of matrix of floating point values

--eigen-ops N

stop after N Eigen matrix computations

--eigen-size N

specify the 2D matrix size N × N. The default is a 32 × 32 matrix.

--efivar N

start N workers that exercise the Linux /sys/firmware/efi/efivars and /sys/firmware/efi/vars interfaces by reading the EFI variables. This is a Linux only stress test for platforms that support the EFI vars interface and may require the CAP_SYS_ADMIN capability.

--efivar-ops N

stop the efivar stressors after N EFI variable read operations.

--enosys N

start N workers that exercise non-functional system call numbers. This calls a wide range of system call numbers to see if it can break a system where these are not wired up correctly. It also keeps track of system calls that exist (ones that don't return ENOSYS) so that it can focus on purely finding and exercising non-functional system calls. This stressor exercises system calls from 0 to __NR_syscalls + 1024, random system calls within constrained in the ranges of 0 to 2↑8, 2↑16, 2↑24, 2↑32, 2↑40, 2↑48, 2↑56 and 2↑64 bits, high system call numbers and various other bit patterns to try to get wide coverage. To keep the environment clean, each system call being tested runs in a child process with reduced capabilities.

--enosys-ops N

stop after N bogo enosys system call attempts

--env N

start N workers that creates numerous large environment variables to try to trigger out of memory conditions using setenv(3). If ENOMEM occurs then the environment is emptied and another memory filling retry occurs. The process is restarted if it is killed by the Out Of Memory (OOM) killer.

--env-ops N

stop after N bogo setenv/unsetenv attempts.

--epoll N

start N workers that perform various related socket stress activity using epoll_wait(2) to monitor and handle new connections. This involves client/server processes performing rapid connect, send/receives and disconnects on the local host. Using epoll allows a large number of connections to be efficiently handled, however, this can lead to the connection table filling up and blocking further socket connections, hence impacting on the epoll bogo op stats. For ipv4 and ipv6 domains, multiple servers are spawned on multiple ports. The epoll stressor is for Linux only.

--epoll-domain D

specify the domain to use, the default is unix (aka local). Currently ipv4, ipv6 and unix are supported.

--epoll-ops N

stop epoll workers after N bogo operations.

--epoll-port P

start at socket port P. For N epoll worker processes, ports P to (P * 4) - 1 are used for ipv4, ipv6 domains and ports P to P - 1 are used for the unix domain.

--epoll-sockets N

specify the maximum number of concurrently open sockets allowed in server. Setting a high value impacts on memory usage and may trigger out of memory conditions.

--eventfd N

start N parent and child worker processes that read and write 8 byte event messages between them via the eventfd mechanism (Linux only).

--eventfd-nonblock

enable EFD_NONBLOCK to allow non-blocking on the event file descriptor. This will cause reads and writes to return with EAGAIN rather the blocking and hence causing a high rate of polling I/O.

--eventfd-ops N

stop eventfd workers after N bogo operations.

--exec N

start N workers continually forking children that exec stress-ng and then exit almost immediately. If a system has pthread support then 1 in 4 of the exec's will be from inside a pthread to exercise exec'ing from inside a pthread context.

--exec-fork-method [ clone | fork | rfork | spawn | vfork ]

select the process creation method using clone(2), fork(2), BSD rfork(2), posix_spawn(3) or vfork(2). Note that vfork will only exec programs using execve due to the constraints on the shared stack between the parent and the child process.

--exec-max P

create P child processes that exec stress-ng and then wait for them to exit per iteration. The default is 4096; higher values may create many temporary zombie processes that are waiting to be reaped. One can potentially fill up the process table using high values for --exec-max and --exec.

--exec-method [ all | execve | execveat ]

select the exec system call to use; all will perform a random choice between execve(2) and execveat(2), execve will use execve(2) and execveat will use execveat(2) if it is available.

--exec-no-pthread

do not use pthread_create(3).

--exec-ops N

stop exec stress workers after N bogo operations.

--exit-group N

start N workers that create 16 pthreads and terminate the pthreads and the controlling child process using exit_group(2). (Linux only stressor).

--exit-group-ops N

stop after N iterations of pthread creation and deletion loops.

--expmath N

start N workers that exercise various exponential functions with input values 0 to 1 in steps of 0.001; the results are sanity checked to ensure no variation occurs after each round of 10000 computations.

--expmath-ops N

stop after N exponential bogo-operation loops.

--expmath-method method

specify a exponential function to exercise. Available exponential stress methods are described as follows:

Method	Description
all	iterate over all the below exponential functions methods
cexp	double complex natural exponential
cexpf	float complex natural exponential
cexpl	long double complex natural exponential
exp	double natural exponential
expf	float natural exponential
expl	long double natural exponential
exp10	double base-10 exponential
exp10f	float base-10 exponential
exp10l	long double base-10 exponential
exp2	double base-2 exponential
exp2f	float base-2 exponential
exp2l	long double base-2 exponential

--factor N

start N workers that factorize large integers using the GNU Multiple Precision Arithmetic Library. Randomized values to be factorized are computed so that an N digit value is comprised of about 0.4 × N random factors, for N > 100. The default number of digits in the value to be factorized is 10.

--factor-digits N

select the number of digits in the values to be factorized. Range 8 to 100000000 digits, default is 10.

--factor-ops N

stop after N factorizations.

-F N, --fallocate N

start N workers continually fallocating (preallocating file space) and ftruncating (file truncating) temporary files. If the file is larger than the free space, fallocate will produce an ENOSPC error which is ignored by this stressor.

--fallocate-bytes N

allocated file size, the default is 1 GB. One can specify the size as % of free space on the file system or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--fallocate-ops N

stop fallocate stress workers after N bogo fallocate operations.

--fanotify N

start N workers performing file system activities such as creating, opening, writing, reading and unlinking files to exercise the fanotify event monitoring interface (Linux only). Each stressor runs a child process to generate file events and a parent process to read file events using fanotify. Has to be run with CAP_SYS_ADMIN capability.

--fanotify-ops N

stop fanotify stress workers after N bogo fanotify events.

--far-branch N

start N workers that exercise calls to tens of thousands of functions that are relatively far from the caller. All functions are 1 op instructions that return to the caller. The functions are placed in pages that are memory mapped with a wide spread of fixed virtual addresses. Function calls are pre-shuffled to create a randomized mix of addresses to call. This stresses the instruction cache and any instruction TLBs.

--far-branch-flush

attempt to periodically flush instruction cache to produce instruction cache misses.

--far-branch-ops N

stop after N far branch bogo-ops. One full cycle of calling all the tens of thousands of functions equates to one bogo-op.

--far-branch-pages N

specify the number of pages to allocate for far branch functions. The number for functions per page depends on the processor architecture, for example, x86 will have 4096 x 1 byte return instructions per 4 K page, where as SPARC64 will have only 512 x 8 byte return instructions per 4 K page.

--fault N

start N workers that generates minor and major page faults.

--fault-ops N

stop the page fault workers after N bogo page fault operations.

--fcntl N

start N workers that perform fcntl(2) calls with various commands. The exercised commands (if available) are: F_DUPFD, F_DUPFD_CLOEXEC, F_GETFD, F_SETFD, F_GETFL, F_SETFL, F_GETOWN, F_SETOWN, F_GETOWN_EX, F_SETOWN_EX, F_GETSIG, F_SETSIG, F_GETLK, F_SETLK, F_SETLKW, F_OFD_GETLK, F_OFD_SETLK and F_OFD_SETLKW.

--fcntl-ops N

stop the fcntl workers after N bogo fcntl operations.

--fd-fork N

start N workers that open files using dup(2) on a file (/dev/zero by default) and then copies these using multiple fork'd child processes and closes them with the fast clone_range(2) or close(2) or by directly ending the processes using _exit(2). For every bogo-op, the stressor attempts to dup(2) another 10000 file descriptors up to the maximum allowed, fork 8 child processes that then close their copies of the file descriptors.

--fd-fork-fds N

specify maximum number of file descriptors to be opened. The default is 2 million, with a range of 1000 to 16 million. The actual number used may be less depending on the system defined limits of the number of open files per process.

--fd-fork-file [ null | random | stdin | stdout | zero ]

specify file to dup: null for /dev/null, random for /dev/random, stdin for standard input, stdout for standard output, zero for /dev/zero. Default is /dev/zero.

--fd-fork-ops N

stop after N rounds of 10000 dups, forking/closing/exiting and waiting for the child processes. Note that the bogo-ops metric rate will slow down over time as this stressor increases the number of open files per bogo-loop and this increases the fork and close run times.

--fd-race N

start N workers that attempt to force race conditions on opened file descriptors. Opened file descriptors are passed from a server to a client over a socket. At periodic intervals batches of the file descriptors are duplicated by creating multiple pthreads and then closed en-masse with synchronized pthread termination. Also other concurrent pthreads exercise various file based system calls on file descriptors that are in the process of being created. By default a single file is used for the open calls, however /dev and /proc files can be exercised using the appropriate fd-race options.

--fd-race-dev

exercise /dev files for race conditions.

--fd-race-race-ops N

stop after N file descriptors have been exercised.

--fd-race-proc

exercise /proc files for race conditions.

--fibsearch N

start N workers that use a search a sorted array of 32 bit integers using a Fibonacci search. A Fibonacci seaarch is similar to a bsearch except that it uses the Fibonacci series to divide the search into unequal sized spaces. It avoids the costly division operator found in bsearches and examines closer elements on each search step so there is a slight compute and cache advantage over bsearch. By default, there are 65536 elements in the array. This is a useful method to exercise random access of memory and processor cache.

--fibsearch-ops N

stop the fibsearch worker after N bogo fibsearch operations are completed.

--fibsearch-size N

specify the size (number of 32 bit integers) in the array to fibsearch. Size can be from 1 K to 4 M.

--fiemap N

start N workers that each create a file with many randomly changing extents and has 4 child processes per worker that gather the extent information using the FS_IOC_FIEMAP ioctl(2).

--fiemap-bytes N

specify the size of the fiemap'd file in bytes. One can specify the size as % of free space on the file system or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g. Larger files will contain more extents, causing more stress when gathering extent information.

--fiemap-ops N

stop after N fiemap bogo operations.

--fifo N

start N workers that exercise a named pipe by transmitting 64 bit integers.

--fifo-data-size N

set the byte size of the fifo write/reads, default is 8, range 8..4096.

--fifo-ops N

stop fifo workers after N bogo pipe write operations.

--fifo-readers N

for each worker, create N fifo reader workers that read the named pipe using simple blocking reads. Default is 4, range 1..64.

--file-ioctl N

start N workers that exercise various file specific ioctl(2) calls. This will attempt to use the FIONBIO, FIOQSIZE, FIGETBSZ, FIOCLEX, FIONCLEX, FIONBIO, FIOASYNC, FIOQSIZE, FIFREEZE, FITHAW, FICLONE, FICLONERANGE, FIONREAD, FIONWRITE and FS_IOC_RESVSP ioctls if these are defined.

--file-ioctl-ops N

stop file-ioctl workers after N file ioctl bogo operations.

--filename N

start N workers that exercise file creation using various length filenames containing a range of allowed filename characters. This will try to see if it can exceed the file system allowed filename length was well as test various filename lengths between 1 and the maximum allowed by the file system.

--filename-ops N

stop filename workers after N bogo filename tests.

--filename-opts opt

use characters in the filename based on option 'opt'. Valid options are:

Option	Description
probe	default option, probe the file system for valid allowed characters in a file name and use these
posix	use characters as specified by The Open Group Base Specifications Issue 7, POSIX.1-2008, 3.278 Portable Filename Character Set
ext	use characters allowed by the ext2, ext3, ext4 file systems, namely any 8 bit character apart from NUL and /

--flock N

start N workers locking on a single file.

--flock-ops N

stop flock stress workers after N bogo flock operations.

--flush-cache N

start N workers that flush the data and instruction cache (where possible). Some architectures may not support cache flushing on either cache, in which case these become no-ops.

--flush-cache-ops N

stop after N cache flush iterations.

--fma N

start N workers that exercise single and double precision floating point multiplication and add operations on arrays of 512 floating point values. More modern processors (Intel Haswell, AMD Bulldozer and Piledriver) and modern C compilers these will be performed by fused-multiply-add (fma3) opcodes. Operations used are:

a = a × b + c

a = b × a + c

a = b × c + a

--fma-libc

use libc fma math functions if they are available. These use either the libc FMA macros if defined, the __builtin libc functions or the fma libc functions. Generally these are slower than directly multiply/add fused code generated by the compiler.

--fma-ops N

stop after N bogo-loops of the 3 above operations on 512 single and double precision floating point numbers.

-f N, --fork N

start N workers continually forking children that immediately exit.

--fork-max P

create P child processes and then wait for them to exit per iteration. The default is just 1; higher values will create many temporary zombie processes that are waiting to be reaped. One can potentially fill up the process table using high values for --fork-max and --fork.

--fork-ops N

stop fork stress workers after N bogo operations.

--fork-pageout

enable force paging-out of memory resident pages in fork stressor instances.

--fork-unmap

attempt to unmap unused non-memory resident shared library pages to try and reduced anonymous vma copying. This is an ugly hack for benchmarking reduced vma copying and not guaranteed to work. Linux only.

--fork-vm

enable detrimental performance virtual memory advice using madvise on all pages of the forked process. Where possible this will try to set every page in the new process with using madvise MADV_MERGEABLE, MADV_WILLNEED, MADV_HUGEPAGE and MADV_RANDOM flags. Linux only.

--forkheavy N

start N workers that fork child processes from a parent that has thousands of allocated system resources. The fork becomes a heavyweight operations as it has to duplicate the resource references of the parent. Each stressor instance creates and reaps up to 4096 child processes that are created and reaped in a first-in first-out manner.

--forkheavy-allocs N

attempt N resource allocation loops per stressor instance. Resources include pipes, file descriptors, memory mappings, pthreads, timers, ptys, semaphores, message queues and temporary files. These create heavyweight processes that are more time expensive to fork from. Default is 16384.

--forkheavy-mlock

attempt to mlock future allocated pages into memory causing more memory pressure. If mlock(MCL_FUTURE) is implemented then this will stop new brk pages from being swapped out.

--forkheavy-ops N

stop after N fork calls.

--forkheavy-procs N

attempt to fork N processes per stressor. The default is 4096 processes.

--fp N

start N workers that exercise addition, multiplication and division operations on a range of floating point types. For each type, 8 floating point values are operated upon 65536 times in a loop per bogo op.

--fp-method method

select the floating point method to use, available methods are:

Method	Description
all	iterate over all the following floating point methods:
float128add	128 bit floating point add
ibm128add	IBM 128 bit floating point add (powerpc)
float80add	80 bit floating point add
float64add	64 bit floating point add
float32add	32 bit binary32 floating point add
floatadd	floating point add
bf16add	bf16 floating point add
doubleadd	double precision floating point add
ldoubleadd	long double precision floating point add
float128mul	128 bit floating point multiply
ibm128mul	IBM 128 bit floating point multiply (powerpc)
float80mul	80 bit floating point multiply
float64mul	64 bit floating point multiply
float32mul	32 bit binary32 floating point multiply
floatmul	floating point multiply
bf16mul	bf16 floating point multiply
doublemul	double precision floating point multiply
ldoublemul	long double precision floating point multiply
float128div	128 bit floating point divide
ibm128div	IBM 128 bit floating point divide (powerpc)
float80div	80 bit floating point divide
float64div	64 bit floating point divide
float32div	32 bit binary32 floating point divide
floatdiv	floating point divide
bf16div	bf16 floating point divide
doublediv	double precision floating point divide
ldoublediv	long double precision floating point divide

--fp-ops N

stop after N floating point bogo ops. Note that bogo-ops are counted for just standard float, double and long double floating point types.

--fp-error N

start N workers that generate floating point exceptions. Computations are performed to force and check for the FE_DIVBYZERO, FE_INEXACT, FE_INVALID, FE_OVERFLOW and FE_UNDERFLOW exceptions. EDOM and ERANGE errors are also checked.

--fp-error-ops N

stop after N bogo floating point exceptions.

--fpunch N

start N workers that punch and fill holes in a 16 MB file using five concurrent processes per stressor exercising on the same file. Where available, this uses fallocate(2) FALLOC_FL_KEEP_SIZE, FALLOC_FL_PUNCH_HOLE, FALLOC_FL_ZERO_RANGE, FALLOC_FL_COLLAPSE_RANGE and FALLOC_FL_INSERT_RANGE to make and fill holes across the file and breaks it into multiple extents.

--fpunch-bytes N

set maximum size of each file for each fpunch worker process, the default is 16 MB. One can specify the size as % of free space on the file system or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--fpunch-ops N

stop fpunch workers after N punch and fill bogo operations.

--fractal N

start N workers that generate 2D fractals. By default a 1024 x 1024 point Mandelbrot set is computed with a maximum of 256 iterations per point in the iterative compute loop. The fractal is computed row by row with multiple rows shared amongst the N fractal stressor instances. Double precision floating point values are used for the points in the complex set of values. Naive computation is used with no special algorithmic short-cuts or interpolation.

--fractal-iterations N

specify the maximum number of iterations for the quadratic map computation of each point, default is 256 iterations.

--fractal-method [ julia | mandelbrot ]

select the method of fractal generation, Julia set or Mandelbrot set, default is the Mandelbrot set.

--fractal-ops N

stop after N fractals have been generated.

--fractal-sizex N

set the maximum width of the fractal, default is 1024 points.

--fractal-sizey N

set the maximum height of the fractal, default is 1024 points.

--fsize N

start N workers that exercise file size limits (via setrlimit RLIMIT_FSIZE) with file sizes that are fixed, random and powers of 2. The files are truncated and allocated to trigger SIGXFSZ signals.

--fsize-ops N

stop after N bogo file size test iterations.

--fstat N

start N workers fstat'ing files in a directory (default is /dev).

--fstat-dir directory

specify the directory to fstat to override the default of /dev. All the files in the directory will be fstat'd repeatedly.

--fstat-ops N

stop fstat stress workers after N bogo fstat operations.

--full N

start N workers that exercise /dev/full. This attempts to write to the device (which should always get error ENOSPC), to read from the device (which should always return a buffer of zeros) and to seek randomly on the device (which should always succeed). (Linux only).

--full-ops N

stop the stress full workers after N bogo I/O operations.

--funccall N

start N workers that call functions of 1 through to 9 arguments. By default all functions with a range of argument types are called, however, this can be changed using the --funccall-method option. This exercises stack function argument passing and re-ordering on the stack and in registers.

--funccall-ops N

stop the funccall workers after N bogo function call operations. Each bogo operation is 1000 calls of functions of 1 through to 9 arguments of the chosen argument type.

--funccall-method method

specify the method of funccall argument type to be used. The default is all the types but can be one of bool, uint8, uint16, uint32, uint64, uint128, float, double, longdouble, cfloat (complex float), cdouble (complex double), clongdouble (complex long double), float16, float32, float64, float80, float128, decimal32, decimal64 and decimal128. Note that some of these types are only available with specific architectures and compiler versions.

--funcret N

start N workers that pass and return by value various small to large data types.

--funcret-ops N

stop the funcret workers after N bogo function call operations.

--funcret-method method

specify the method of funcret argument type to be used. The default is uint64_t but can be one of uint8 uint16 uint32 uint64 uint128 float double longdouble float80 float128 decimal32 decimal64 decimal128 uint8x32 uint8x128 uint64x128.

--futex N

start N workers that rapidly exercise the futex system call. Each worker has two processes, a futex waiter and a futex waker. The waiter waits with a very small timeout to stress the timeout and rapid polled futex waiting. This is a Linux specific stress option.

--futex-ops N

stop futex workers after N bogo successful futex wait operations.

--get N

start N workers that call system calls that fetch data from the kernel, currently these are: getpid, getppid, getcwd, getgid, getegid, getuid, getgroups, getpgrp, getpgid, getpriority, getresgid, getresuid, getrlimit, prlimit, getrusage, getsid, gettid, getcpu, gettimeofday, uname, adjtimex, sysfs. Some of these system calls are OS specific.

--get-ops N

stop get workers after N bogo get operations.

--get-slow-sync

attempt to synchronize system calls across the N get workers to try to force forms of locking contention in the kernel on the more complex cases. Each system call is exercised concurrently with the N workers for 0.1 seconds at a time, so it takes a 3-4 seconds to work through all the system calls.

--getdent N

start N workers that recursively read directories /proc, /dev/, /tmp, /sys and /run using getdents and getdents64 (Linux only).

--getdent-ops N

stop getdent workers after N bogo getdent bogo operations.

--getrandom N

start N workers that get 8192 random bytes from the /dev/urandom pool using the getrandom(2) system call (Linux) or getentropy(2) (OpenBSD).

--getrandom-ops N

stop getrandom workers after N bogo get operations.

--goto N

start N workers that perform 1024 forward branches (to next instruction) or backward branches (to previous instruction) for each bogo operation loop. By default, every 1024 branches the direction is randomly chosen to be forward or backward. This stressor exercises suboptimal pipelined execution and branch prediction logic.

--goto-direction [ forward | backward | random ]

select the branching direction in the stressor loop, forward for forward only branching, backward for a backward only branching, random for a random choice of forward or random branching every 1024 branches.

--goto-ops N

stop goto workers after N bogo loops of 1024 branch instructions.

--gpu N

start N worker that exercise the GPU. This specifies a 2-D texture image that allows the elements of an image array to be read by shaders, and render primitives using an opengl context.

--gpu-devnode DEVNAME

specify the device node name of the GPU device, the default is /dev/dri/renderD128.

--gpu-frag N

specify shader core usage per pixel, this sets N loops in the fragment shader.

--gpu-ops N

stop gpu workers after N render loop operations.

--gpu-tex-size N

specify upload texture N × N, by default this value is 4096 × 4096.

--gpu-xsize X

use a framebuffer size of X pixels. The default is 256 pixels.

--gpu-ysize Y

use a framebuffer size of Y pixels. The default is 256 pixels.

--gpu-upload N

specify upload texture N times per frame, the default value is 1.

--handle N

start N workers that exercise the name_to_handle_at(2) and open_by_handle_at(2) system calls. (Linux only).

--handle-ops N

stop after N handle bogo operations.

--hash N

start N workers that exercise various hashing functions. Random strings from 1 to 128 bytes are hashed and the hashing rate and chi squared is calculated from the number of hashes performed over a period of time. The chi squared value is the goodness-of-fit measure, it is the actual distribution of items in hash buckets versus the expected distribution of items. Typically a chi squared value of 0.95..1.05 indicates a good hash distribution.

--hash-method method

specify the hashing method to use, by default all the hashing methods are cycled through. Methods available are:

Method	Description
all	cycle through all the hashing methods
adler32	Mark Adler checksum, a modification of the Fletcher checksum
coffin	xor and 5 bit rotate left hash
coffin32	xor and 5 bit rotate left hash with 32 bit fetch optimization
crc32c	compute CRC32C (Castagnoli CRC32) integer hash
djb2a	Dan Bernstein hash using the xor variant
fnv1a	FNV-1a Fowler-Noll-Vo hash using the xor then multiply variant
jenkin	Jenkin's integer hash
kandr	Kernighan and Richie's multiply by 31 and add hash from "The C Programming Language", 2nd Edition
knuth	Donald E. Knuth's hash from "The Art Of Computer Programming", Volume 3, chapter 6.4
loselose	Kernighan and Richie's simple hash from "The C Programming Language", 1st Edition
mid5	xor shift hash of the middle 5 characters of the string. Designed by Colin Ian King
muladd32	simple multiply and add hash using 32 bit math and xor folding of overflow
muladd64	simple multiply and add hash using 64 bit math and xor folding of overflow
mulxror32	32 bit multiply, xor and rotate right. Mangles 32 bits where possible. Designed by Colin Ian King
mulxror64	64 bit multiply, xor and rotate right. 64 Bit version of mulxror32
murmur3_32	murmur3_32 hash, Austin Appleby's Murmur3 hash, 32 bit variant
nhash	exim's nhash.
pjw	a non-cryptographic hash function created by Peter J. Weinberger of AT&T Bell Labs, used in UNIX ELF object files
sdbm	sdbm hash as used in the SDBM database and GNU awk
sedgwick	simple hash from Robert Sedgwick's C programming book
sobel	Justin Sobel's bitwise shift hash
x17	multiply by 17 and add. The multiplication can be optimized down to a fast right shift by 4 and add on some architectures
xor	simple rotate shift and xor of values
xorror32	32 bit exclusive-or with right rotate hash, a fast string hash, designed by Colin Ian King
xorror64	64 bit version of xorror32
xxhash	the "Extremely fast" hash in non-streaming mode

--hash-ops N

stop after N hashing rounds

-d N, --hdd N

start N workers continually writing, reading and removing temporary files. The default mode is to stress test sequential writes and reads. With the --aggressive option enabled without any --hdd-opts options the hdd stressor will work through all the --hdd-opt options one by one to cover a range of I/O options.

--hdd-bytes N

write N bytes for each hdd process, the default is 1 GB. One can specify the size as % of free space on the file system or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--hdd-opts list

specify various stress test options as a comma separated list. Options are as follows:

Option	Description
direct	try to minimize cache effects of the I/O. File I/O writes are performed directly from user space buffers and synchronous transfer is also attempted. To guarantee synchronous I/O, also use the sync option.
dsync	ensure output has been transferred to underlying hardware and file metadata has been updated (using the O_DSYNC open flag). This is equivalent to each write(2) being followed by a call to fdatasync(2). See also the fdatasync option.
fadv-dontneed	advise kernel to expect the data will not be accessed in the near future.
fadv-noreuse	advise kernel to expect the data to be accessed only once.
fadv-normal	advise kernel there are no explicit access pattern for the data. This is the default advice assumption.
fadv-rnd	advise kernel to expect random access patterns for the data.
fadv-seq	advise kernel to expect sequential access patterns for the data.
fadv-willneed	advise kernel to expect the data to be accessed in the near future.
fsync	flush all modified in-core data after each write to the output device using an explicit fsync(2) call.
fdatasync	similar to fsync, but do not flush the modified metadata unless metadata is required for later data reads to be handled correctly. This uses an explicit fdatasync(2) call.
iovec	use readv/writev multiple buffer I/Os rather than read/write. Instead of 1 read/write operation, the buffer is broken into an iovec of 16 buffers.
noatime	do not update the file last access timestamp, this can reduce metadata writes.
sync	ensure output has been transferred to underlying hardware (using the O_SYNC open flag). This is equivalent to a each write(2) being followed by a call to fsync(2). See also the fsync option.
rd-rnd	read data randomly.
rd-seq	read data sequentially.
syncfs	write all buffered modifications of file metadata and data on the filesystem that contains the hdd worker files.
utimes	force update of file timestamp which may increase metadata writes.
wr-rnd	write data randomly. The wr-seq option cannot be used at the same time.
wr-seq	write data sequentially. This is the default if no write modes are specified.

Note that some of these options are mutually exclusive, for example, there can be only one method of writing or reading. Also, fadvise flags may be mutually exclusive, for example fadv-willneed cannot be used with fadv-dontneed.

--hdd-ops N

stop hdd stress workers after N bogo operations.

--hdd-write-size N

specify size of each write in bytes. Size can be from 1 byte to 4 MB.

--heapsort N

start N workers that sort 32 bit integers using the BSD heapsort.

--heapsort-method [ heapsort-libc | heapsort-nonlibc ]

select either the libc implementation of heapsort or an optimized implementation of heapsort. The default is the libc implementation if it is available.

--heapsort-ops N

stop heapsort stress workers after N bogo heapsorts.

--heapsort-size N

specify number of 32 bit integers to sort, default is 262144 (256 × 1024).

--hrtimers N

start N workers that exercise high resolution times at a high frequency. Each stressor starts 32 processes that run with random timer intervals of 0..499999 nanoseconds. Running this stressor with appropriate privilege will run these with the SCHED_RR policy.

--hrtimers-adjust

enable automatic timer rate adjustment to try to maximize the hrtimer frequency. The signal rate is measured every 0.1 seconds and the hrtimer delay is adjusted to try and set the optimal hrtimer delay to generate the highest hrtimer rates.

--hrtimers-ops N

stop hrtimers stressors after N timer event bogo operations

--hsearch N

start N workers that search a 80% full hash table using hsearch(3). By default, there are 8192 elements inserted into the hash table. This is a useful method to exercise access of memory and processor cache.

--hsearch-method [ hsearch-libc | hsearch-nonlibc ]

select either the libc implementation of hsearch or a slightly optimized non-libc implementation of hsearch. The default is the libc implementation if it exists, otherwise the non-libc version.

--hsearch-ops N

stop the hsearch workers after N bogo hsearch operations are completed.

--hsearch-size N

specify the number of hash entries to be inserted into the hash table. Size can be from 1 K to 4 M.

--hyperbolic N

start N workers that exercise sinh, cosh, and tanh hyperbolic functions using float, double and long double floating point variants. Each function is exercised 10,000 times per bogo-operation.

--hyperbolic-method function

specify a hyperbolic stress function. By default, all the functions are exercised sequentially, however one can specify just one function to be used if required. Available options are as follows:

Method	Description
all	iterate through all of the following hyperbolic functions
cosh	hyperbolic cosine (double precision)
coshf	hyperbolic cosine (float precision)
coshl	hyperbolic cosine (long double precision)
sinh	hyperbolic sine (double precision)
sinhf	hyperbolic sine (float precision)
sinhl	hyperbolic sine (long double precision)
tanh	hyperbolic tangent (double precision)
tanhf	hyperbolic tangent (float precision)
tanhl	hyperbolic tangent (long double precision)

--hyperbolic-ops N

stop after N bogo-operations.

--icache N

start N workers that stress the instruction cache by forcing instruction cache reloads.

--icache-ops N

stop the icache workers after N bogo icache operations are completed.

--icmp-flood N

start N workers that flood localhost with randonly sized ICMP ping packets. This stressor requires the CAP_NET_RAW capbility.

--icmp-flood-max-size

use a maximum packet size of 65535 bytes instead of the default of 1000 bytes.

--icmp-flood-ops N

stop icmp flood workers after N ICMP ping packets have been sent.

--idle-scan N

start N workers that scan the idle page bitmap across a range of physical pages. This sets and checks for idle pages via the idle page tracking interface /sys/kernel/mm/page_idle/bitmap. This is for Linux only.

--idle-scan-ops N

stop after N bogo page scan operations. Currently one bogo page scan operation is equivalent to setting and checking 64 physical pages.

--idle-page N

start N workers that walks through every page exercising the Linux /sys/kernel/mm/page_idle/bitmap interface. Requires CAP_SYS_RESOURCE capability.

--idle-page-ops N

stop after N bogo idle page operations.

--inode-flags N

start N workers that exercise inode flags using the FS_IOC_GETFLAGS and FS_IOC_SETFLAGS ioctl(2). This attempts to apply all the available inode flags onto a directory and file even if the underlying file system may not support these flags (errors are just ignored). Each worker runs 4 threads that exercise the flags on the same directory and file to try to force races. This is a Linux only stressor, see ioctl_iflags(2) for more details.

--inode-flags-ops N

stop the inode-flags workers after N ioctl flag setting attempts.

--inotify N

start N workers performing file system activities such as making/deleting files/directories, moving files, etc. to stress exercise the various inotify events (Linux only).

--inotify-ops N

stop inotify stress workers after N inotify bogo operations.

--insertionsort N

start N workers that sort 32 bit integers using insertion sort.

--insertionsort-ops N

stop insertionsort stress workers after N bogo insertion sorts.

--insertionsort-size N

specify number of 32 bit integers to sort, default is 16384 (16 × 1024).

--intmath N

start N workers that perform addition, subtraction, multiplication, division and modulo math operations on 128, 64, 32, 16 and 8 bit signed integers.

--intmath-method method

select the integer math method to use, available methods are:

Method	Description
all	iterate over all the following integer methods:
add128	128 bit signed integer addition
add64	64 bit signed integer addition
add32	32 bit signed integer addition
add16	16 bit signed integer addition
add8	8 bit signed integer addition
sub128	128 bit signed integer subtraction
sub64	64 bit signed integer subtraction
sub32	32 bit signed integer subtraction
sub16	16 bit signed integer subtraction
sub8	8 bit signed integer subtraction
mul128	128 bit signed integer multiplication
mul64	64 bit signed integer multiplication
mul32	32 bit signed integer multiplication
mul16	16 bit signed integer multiplication
mul8	8 bit signed integer multiplication
div128	128 bit signed integer division
div64	64 bit signed integer division
div32	32 bit signed integer division
div16	16 bit signed integer division
div8	8 bit signed integer division
mod128	128 bit signed integer modulo
mod64	64 bit signed integer modulo
mod32	32 bit signed integer modulo
mod16	16 bit signed integer modulo
mod8	8 bit signed integer modulo

--intmath-ops N

stop intmath workers after N bogo integer math operations.

-i N, --io N

start N workers continuously calling sync(2) to commit buffer cache to disk. This can be used in conjunction with the --hdd stressor. This is a legacy stressor that is compatible with the original stress tool.

--io-ops N

stop io stress workers after N bogo operations.

--iomix N

start N workers that perform a mix of sequential, random and memory mapped read/write operations as well as random copy file read/writes, forced sync'ing and (if run as root) cache dropping. Multiple child processes are spawned to all share a single file and perform different I/O operations on the same file.

--iomix-bytes N

write N bytes for each iomix worker process, the default is 1 GB. One can specify the size as % of free space on the file system or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--iomix-ops N

stop iomix stress workers after N bogo iomix I/O operations.

--ioport N

start N workers than perform bursts of 16 reads and 16 writes of ioport 0x80 (x86 Linux systems only). I/O performed on x86 platforms on port 0x80 will cause delays on the CPU performing the I/O.

--ioport-ops N

stop the ioport stressors after N bogo I/O operations

--ioport-opts [ in | out | inout ]

to be performed. The default is both in and out. specify if port reads in, port read writes out or reads and writes are

--ioprio N

start N workers that exercise the ioprio_get(2) and ioprio_set(2) system calls (Linux only).

--ioprio-ops N

stop after N io priority bogo operations.

--io-uring N

start N workers that perform various io-uring file operations using the Linux io-uring interface.

--io-uring-entries N

specify the number of io-uring ring entries.

--io-uring-ops

stop after N rounds of io-uring operations.

--io-uring-rand

randomize order of io-uring operations and file seek locations.

--ipsec-mb N

start N workers that perform cryptographic processing using the highly optimized Intel Multi-Buffer Crypto for IPsec library. Depending on the features available, SSE, AVX, AVX and AVX512 CPU features will be used on data encrypted by SHA, DES, CMAC, CTR, HMAC MD5, HMAC SHA1 and HMAC SHA512 cryptographic routines. This is only available for x86-64 modern Intel CPUs.

--ipsec-mb-feature [ sse | avx | avx2 | avx512 | noaesni ]

Just use the specified processor CPU feature. By default, all the available features for the CPU are exercised.

--ipsec-mb-jobs N

Process N multi-block rounds of cryptographic processing per iteration. The default is 256.

--ipsec-mb-method [ all | cmac | ctr | des | hmac-md5 | hmac-sha1 | hmac-sha512 | sha ]

Select the ipsec-mb crypto/integrity method.

--ipsec-mb-ops N

stop after N rounds of processing of data using the cryptographic routines.

--itimer N

start N workers that exercise the system interval timers. This sets up an ITIMER_PROF itimer that generates a SIGPROF signal. The default frequency for the itimer is 1 MHz, however, the Linux kernel will set this to be no more that the jiffy setting, hence high frequency SIGPROF signals are not normally possible. A busy loop spins on getitimer(2) calls to consume CPU and hence decrement the itimer based on amount of time spent in CPU and system time.

--itimer-freq F

run itimer at F Hz; range from 1 to 1000000 Hz. Normally the highest frequency is limited by the number of jiffy ticks per second, so running above 1000 Hz is difficult to attain in practice.

--itimer-ops N

stop itimer stress workers after N bogo itimer SIGPROF signals.

--itimer-rand

select an interval timer frequency based around the interval timer frequency +/- 12.5% random jitter. This tries to force more variability in the timer interval to make the scheduling less predictable.

--jpeg N

start N workers that use jpeg compression on a machine generated plasma field image. The default image is a plasma field, however different image types may be selected. The starting raster line is changed on each compression iteration to cycle around the data.

--jpeg-height H

use a RGB sample image height of H pixels. The default is 512 pixels.

--jpeg-image [ brown | flat | gradient | noise | plasma | xstripes ]

select the source image type to be compressed. Available image types are:

Type	Description
brown	brown noise, red and green values vary by a 3 bit value, blue values vary by a 2 bit value.
flat	a single random colour for the entire image.
gradient	linear gradient of the red, green and blue components across the width and height of the image.
noise	random white noise for red, green, blue values.
plasma	plasma field with smooth colour transitions and hard boundary edges.
xstripes	a random colour for each horizontal line.

--jpeg-ops N

stop after N jpeg compression operations.

--jpeg-quality Q

use the compression quality Q. The range is 1..100 (1 lowest, 100 highest), with a default of 95

--jpeg-width H

use a RGB sample image width of H pixels. The default is 512 pixels.

--judy N

start N workers that insert, search and delete 32 bit integers in a Judy array using a predictable yet sparse array index. By default, there are 131072 integers used in the Judy array. This is a useful method to exercise random access of memory and processor cache.

--judy-ops N

stop the judy workers after N bogo judy operations are completed.

--judy-size N

specify the size (number of 32 bit integers) in the Judy array to exercise. Size can be from 1 K to 4 M 32 bit integers.

--kcmp N

start N workers that use kcmp(2) to compare parent and child processes to determine if they share kernel resources. Supported only for Linux and requires CAP_SYS_PTRACE capability.

--kcmp-ops N

stop kcmp workers after N bogo kcmp operations.

--key N

start N workers that create and manipulate keys using add_key(2) and ketctl(2). As many keys are created as the per user limit allows and then the following keyctl commands are exercised on each key: KEYCTL_SET_TIMEOUT, KEYCTL_DESCRIBE, KEYCTL_UPDATE, KEYCTL_READ, KEYCTL_CLEAR and KEYCTL_INVALIDATE.

--key-ops N

stop key workers after N bogo key operations.

--kill N

start N workers sending SIGUSR1 kill signals to a SIG_IGN signal handler in the stressor and SIGUSR1 kill signal to a child stressor with a SIGUSR1 handler. Most of the process time will end up in kernel space.

--kill-ops N

stop kill workers after N bogo kill operations.

--klog N

start N workers exercising the kernel syslog(2) system call. This will attempt to read the kernel log with various sized read buffers. Linux only.

--klog-ops N

stop klog workers after N syslog operations.

--kvm N

start N workers that create, run and destroy a minimal virtual machine. The virtual machine reads, increments and writes to port 0x80 in a spin loop and the stressor handles the I/O transactions. Currently for x86 and Linux only.

--kvm-ops N

stop kvm stressors after N virtual machines have been created, run and destroyed.

--l1cache N

start N workers that exercise the CPU level 1 cache with reads and writes. A cache aligned buffer that is twice the level 1 cache size is read and then written in level 1 cache set sized steps over each level 1 cache set. This is designed to exercise cache block evictions. The bogo-op count measures the number of million cache lines touched. Where possible, the level 1 cache geometry is determined from the kernel, however, this is not possible on some architectures or kernels, so one may need to specify these manually. One can specify 3 out of the 4 cache geometric parameters, these are as follows:

--l1cache-line-size N

specify the level 1 cache line size (in bytes)

--l1cache-method [ forward | random | reverse ]

select the method of exercising a l1cache sized buffer. The default is a forward scan, random picks random bytes to exercise, reverse scans in reverse.

--l1cache-mlock

attempt to mlock the l1cache size buffer into memory to prevent it from being swapped out.

--l1cache-ops N

specify the number of cache read/write bogo-op loops to run

--l1cache-sets N

specify the number of level 1 cache sets

--l1cache-size N

specify the level 1 cache size (in bytes)

--l1cache-ways N

specify the number of level 1 cache ways

--landlock N

start N workers that exercise Linux 5.13 landlocking. A range of landlock_create_ruleset flags are exercised with a read only file rule to see if a directory can be accessed and a read-write file create can be blocked. Each ruleset attempt is exercised in a new child context and this is the limiting factor on the speed of the stressor.

--landlock-ops N

stop the landlock stressors after N landlock ruleset bogo operations.

--lease N

start N workers locking, unlocking and breaking leases via the fcntl(2) F_SETLEASE operation. The parent processes continually lock and unlock a lease on a file while a user selectable number of child processes open the file with a non-blocking open to generate SIGIO lease breaking notifications to the parent. This stressor is only available if F_SETLEASE, F_WRLCK and F_UNLCK support is provided by fcntl(2).

--lease-breakers N

start N lease breaker child processes per lease worker. Normally one child is plenty to force many SIGIO lease breaking notification signals to the parent, however, this option allows one to specify more child processes if required.

--lease-ops N

stop lease workers after N bogo operations.

--led N

start N workers that exercise the /sys/class/leds interfaces to set LED brightness levels and the various trigger settings. This needs to be run with root privilege to be able to write to these settings successfully. Non-root privilege will ignore failed writes.

--led-ops N

stop after N interfaces are exercised.

--link N

start N workers creating and removing hardlinks.

--link-ops N

stop link stress workers after N bogo operations.

--link-sync

sync dirty data and metadata to disk.

--list N

start N workers that exercise list data structures. The default is to add, find and remove 5,000 64 bit integers into circleq (doubly linked circle queue), list (doubly linked list), slist (singly linked list), slistt (singly linked list using tail), stailq (singly linked tail queue) and tailq (doubly linked tail queue) lists. The intention of this stressor is to exercise memory and cache with the various list operations.

--list-method [ all | circleq | list | slist | stailq | tailq ]

specify the list to be used. By default, all the list methods are used (the 'all' option).

--list-ops N

stop list stressors after N bogo ops. A bogo op covers the addition, finding and removing all the items into the list(s).

--list-size N

specify the size of the list, where N is the number of 64 bit integers to be added into the list.

--llc-affinity N

start N workers that exercise the last level of cache (LLC) by read/write activity across a LLC sized buffer and then changing CPU affinity after each round of read/writes. This can cause non-local memory stalls and LLC read/write misses.

--llc-affinity-mlock

attempt to mlock the LLC sized buffer into memory to prevent it from being swapped out.

--llc-affinity-ops N

stop after N rounds of LLC read/writes.

--loadavg N

start N workers that attempt to create thousands of pthreads that run at the lowest nice priority to force very high load averages. Linux systems will also perform some I/O writes as pending I/O is also factored into system load accounting.

--loadavg-max N

set the maximum number of pthreads to create to N. N may be reduced if there is as system limit on the number of pthreads that can be created.

--loadavg-ops N

stop loadavg workers after N bogo scheduling yields by the pthreads have been reached.

--lockbus N

start N workers that rapidly lock and increment 64 bytes of randomly chosen memory from a 16 MB mmap'd region (Intel x86 and ARM CPUs only). This will cause cacheline misses and stalling of CPUs.

--lockbus-nosplit

disable split locks that lock across cache line boundaries.

--lockbus-ops N

stop lockbus workers after N bogo operations.

--locka N

start N workers that randomly lock and unlock regions of a file using the POSIX advisory locking mechanism (see fcntl(2), F_SETLK, F_GETLK). Each worker creates a 1024 KB file and attempts to hold a maximum of 1024 concurrent locks with a child process that also tries to hold 1024 concurrent locks. Old locks are unlocked in a first-in, first-out basis.

--locka-ops N

stop locka workers after N bogo locka operations.

--lockf N

start N workers that randomly lock and unlock regions of a file using the POSIX lockf(3) locking mechanism. Each worker creates a 64 KB file and attempts to hold a maximum of 1024 concurrent locks with a child process that also tries to hold 1024 concurrent locks. Old locks are unlocked in a first-in, first-out basis.

--lockf-nonblock

instead of using blocking F_LOCK lockf(3) commands, use non-blocking F_TLOCK commands and re-try if the lock failed. This creates extra system call overhead and CPU utilisation as the number of lockf workers increases and should increase locking contention.

--lockf-ops N

stop lockf workers after N bogo lockf operations.

--lockmix N

start N workers that randomly lock and unlock regions of a file using the BSD flock, locka (advisory), POSIX lockf and Linux open file lock (lockofd) locking mechanisms. Each worker creates a 1024 KB file and attempts to hold a maximum of 1024 concurrent locks with a child process that also tries to hold 1024 concurrent locks. Old locks are unlocked in a first-in, first-out basis.

--lockmix-ops N

stop lockmix workers after N bogo lockmix operations.

--lockofd N

start N workers that randomly lock and unlock regions of a file using the Linux open file description locks (see fcntl(2), F_OFD_SETLK, F_OFD_GETLK). Each worker creates a 1024 KB file and attempts to hold a maximum of 1024 concurrent locks with a child process that also tries to hold 1024 concurrent locks. Old locks are unlocked in a first-in, first-out basis.

--lockofd-ops N

stop lockofd workers after N bogo lockofd operations.

--logmath N

start N workers that exercise various logarithmic functions with input values 1 to 10000. Results are sanity checked to ensure no variation occurs after each round of 10000 computations.

--logmath-ops N

stop after N logarithmic bogo-operation loops.

--logmath-method method

specify a logarithmic function to exercise. Available logarithmic stress methods are described as follows:

Method	Description
all	iterate over all the below logarithmic functions methods
clog	double complex natural logarithm
clogf	float complex natural logarithm
clogl	long double complex natural logarithm
log	double natural logarithm
logf	float natural logarithm
logl	long double natural logarithm
logb	get exponent of a double
logbf	get exponent of a float
logbl	get exponent of a long double
log10	double base-10 logarithm
log10f	float base-10 logarithm
log10l	long double base-10 logarithm
log2	double base-2 logarithm
log2f	float base-2 logarithm
log2l	long double base-2 logarithm

--longjmp N

start N workers that exercise setjmp(3)/longjmp(3) by rapid looping on longjmp calls.

--longjmp-ops N

stop longjmp stress workers after N bogo longjmp operations (1 bogo op is 1000 longjmp calls).

--loop N

start N workers that exercise the loopback control device. This creates 2 MB loopback devices, expands them to 4 MB, performs some loopback status information get and set operations and then destoys them. Linux only and requires CAP_SYS_ADMIN capability.

--loop-ops N

stop after N bogo loopback creation/deletion operations.

--lsearch N

start N workers that linear search a unsorted array of 32 bit integers using lsearch(3). By default, there are 8192 elements in the array. This is a useful method to exercise sequential access of memory and processor cache.

--lsearch-method [ lsearch-libc | lsearch-nonlibc | lsearch-sentinel ]

select either the libc implementation of lsearch or a slightly optimized non-libc implementation of lsearch or a lsearch that uses the search key as the end of array sentinel to remove an index compare per loop. The default is the libc implementation if it exists, otherwise the non-libc version.

--lsearch-ops N

stop the lsearch workers after N bogo lsearch operations are completed.

--lsearch-size N

specify the size (number of 32 bit integers) in the array to lsearch. Size can be from 1 K to 4 M.

--lsm N

start N workers that exercise the LSM system calls lsm_list_modules and lsm_get_self_attr, (Linux only). Each bogo-op loop fetches a list of available security modules and fetching LSM attributes as well as some invalid LSM system calls to exercise error handling.

--lsm-ops N

stop after N loops of fetching security modules lists and fetching LSM attributes.

--madvise N

start N workers that apply random madvise(2) advise settings on pages of a 4 MB file backed shared memory mapping.

--madvise-hwpoison

enable MADV_HWPOISON page poisoning (if available, only when run as root). This will page poison a few pages and will cause kernel error messages to be reported.

--madvise-ops N

stop madvise stressors after N bogo madvise operations.

--malloc N

start N workers continuously calling malloc(3), calloc(3), realloc(3), posix_memalign(3), aligned_alloc(3), memalign(3) and free(3). By default, up to 65536 allocations can be active at any point, but this can be altered with the --malloc-max option. Allocation, reallocation and freeing are chosen at random; 50% of the time memory is allocation (via one of malloc, calloc or realloc, posix_memalign, aligned_alloc, memalign) and 50% of the time allocations are free'd. Allocation sizes are also random, with the maximum allocation size controlled by the --malloc-bytes option, the default size being 64 K. The worker is re-started if it is killed by the out of memory (OOM) killer.

--malloc-bytes N

maximum per allocation/reallocation size. Allocations are randomly selected from 1 to N bytes. One can specify the size as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g. Large allocation sizes cause the memory allocator to use mmap(2) rather than expanding the heap using brk(2).

--malloc-max N

maximum number of active allocations allowed. Allocations are chosen at random and placed in an allocation slot. Because about 50%/50% split between allocation and freeing, typically half of the allocation slots are in use at any one time.

--malloc-mlock

attempt to mlock the allocations into memory to prevent them from being swapped out.

--malloc-ops N

stop after N malloc bogo operations. One bogo operations relates to a successful malloc(3), calloc(3) or realloc(3).

--malloc-pthreads N

specify number of malloc stressing concurrent pthreads to run. The default is 0 (just one main process, no pthreads). This option will do nothing if pthreads are not supported.

--malloc-thresh N

specify the threshold where malloc uses mmap(2) instead of sbrk(2) to allocate more memory. This is only available on systems that provide the GNU C mallopt(3) tuning function.

--malloc-touch

touch every allocated page to force pages to be populated in memory. This will increase the memory pressure and exercise the virtual memory harder. By default the malloc stressor will madvise pages into memory or use mincore to check for non-resident memory pages and try to force them into memory; this option aggressively forces pages to be memory resident.

--malloc-trim

periodically trim memory allocation by attempting to release free memory from the heap every 65536 allocation iterations. This can be a time consuming operation. It is only available with libc malloc implementations that support malloc_trim(3).

--malloc-zerofree

zero allocated memory before free'ing. This can be useful in touching broken allocations and triggering failures. Also useful for forcing extra cache/memory writes.

--matrix N

start N workers that perform various matrix operations on floating point values. Testing on 64 bit x86 hardware shows that this provides a good mix of memory, cache and floating point operations and is an excellent way to make a CPU run hot.

By default, this will exercise all the matrix stress methods one by one on a 128 × 128 element matrix. One can specify a specific matrix stress method with the --matrix-method option.

--matrix-method method

specify a matrix stress method. Available matrix stress methods are described as follows:

Method	Description
all	iterate over all the below matrix stress methods
add	add two N × N matrices
copy	copy one N × N matrix to another
div	divide an N × N matrix by a scalar
frobenius	Frobenius product of two N × N matrices
hadamard	Hadamard product of two N × N matrices
identity	create an N × N identity matrix
mean	arithmetic mean of two N × N matrices
mult	multiply an N × N matrix by a scalar
negate	negate an N × N matrix
prod	product of two N × N matrices
sub	subtract one N × N matrix from another N × N matrix
square	multiply an N × N matrix by itself
trans	transpose an N × N matrix
zero	zero an N × N matrix

--matrix-ops N

stop matrix stress workers after N bogo operations.

--matrix-size N

specify the N × N size of the matrices. Smaller values result in a floating point compute throughput bound stressor, where as large values result in a cache and/or memory bandwidth bound stressor.

--matrix-yx

perform matrix operations in order y by x rather than the default x by y. This is suboptimal ordering compared to the default and will perform more data cache stalls.

--matrix-3d N

start N workers that perform various 3D matrix operations on floating point values. Testing on 64 bit x86 hardware shows that this provides a good mix of memory, cache and floating point operations and is an excellent way to make a CPU run hot.

By default, this will exercise all the 3D matrix stress methods one by one on a 128 × 128 × 128 element matrix. One can specify a specific 3D matrix stress method with the --matrix-3d-method option.

--matrix-3d-method method

specify a 3D matrix stress method. Available 3D matrix stress methods are described as follows:

Method	Description
all	iterate over all the below matrix stress methods
add	add two N × N × N matrices
copy	copy one N × N × N matrix to another
div	divide an N × N × N matrix by a scalar
frobenius	Frobenius product of two N × N × N matrices
hadamard	Hadamard product of two N × N × N matrices
identity	create an N × N × N identity matrix
mean	arithmetic mean of two N × N × N matrices
mult	multiply an N × N × N matrix by a scalar
negate	negate an N × N × N matrix
sub	subtract one N × N × N matrix from another N × N × N matrix
trans	transpose an N × N × N matrix
zero	zero an N × N × N matrix

--matrix-3d-ops N

stop the 3D matrix stress workers after N bogo operations.

--matrix-3d-size N

specify the N × N × N size of the matrices. Smaller values result in a floating point compute throughput bound stressor, where as large values result in a cache and/or memory bandwidth bound stressor.

--matrix-3d-zyx

perform matrix operations in order z by y by x rather than the default x by y by z. This is suboptimal ordering compared to the default and will perform more data cache stalls.

--mcontend N

start N workers that produce memory contention read/write patterns. Each stressor runs with 5 threads that read and write to two different mappings of the same underlying physical page. Various caching operations are also exercised to cause sub-optimal memory access patterns. The threads also randomly change CPU affinity to exercise CPU and memory migration stress.

--mcontend-ops N

stop mcontend stressors after N bogo read/write operations.

--membarrier N

start N workers that exercise the membarrier system call (Linux only).

--membarrier-ops N

stop membarrier stress workers after N bogo membarrier operations.

--memcpy N

start N workers that copies data to and from a buffer using memcpy(3) and then move the data in the buffer with memmove(3) with 3 different alignments. This will exercise the data cache and memory copying.

--memcpy-method [ all | libc | builtin | naive | naive_o0 .. naive_o3 ]

specify a memcpy copying method. Available memcpy methods are described as follows:

Method	Description
all	use libc, builtin and naïve methods
libc	use libc memcpy and memmove functions, this is the default
builtin	use the compiler built in optimized memcpy and memmove functions
naive	use naïve byte by byte copying and memory moving build with default compiler optimization flags
naive_o0	use unoptimized naïve byte by byte copying and memory moving
naive_o1	use unoptimized naïve byte by byte copying and memory moving with -O1 optimization
naive_o2	use optimized naïve byte by byte copying and memory moving build with -O2 optimization and where possible use CPU specific optimizations
naive_o3	use optimized naïve byte by byte copying and memory moving build with -O3 optimization and where possible use CPU specific optimizations

--memcpy-ops N

stop memcpy stress workers after N bogo memcpy operations.

--memfd N

start N workers that create allocations of 1024 pages using memfd_create(2) and ftruncate(2) for allocation and mmap(2) to map the allocation into the process address space. (Linux only).

--memfd-bytes N

allocate N bytes per memfd stress worker, the default is 256 MB. One can specify the size in as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--memfd-fds N

create N memfd file descriptors, the default is 256. One can select 8 to 4096 memfd file descriptions with this option.

--memfd-madvise

enable random madvise page advice on memfd memory mapped regions to add a little more VM exercising.

--memfd-mlock

attempt to mlock mmap'd pages into memory causing more memory pressure by preventing pages from swapped out.

--memfd-ops N

stop after N memfd-create(2) bogo operations.

--memfd-zap-pte

exercise zapping page-table-entries to try to reproduce a Linux kernel bug that was fixed by commit 5abfd71d936a8aefd9f9ccd299dea7a164a5d455 "mm: don't skip swap entry even if zap_details specified". This will slow the stressor down significantly and hence is an opt-in memfd stressor option.

--memhotplug N

start N workers that offline and online memory hotplug regions. Linux only and requires CAP_SYS_ADMIN capabilities.

-mhotplug-mmap

enable random 1 K to 1 MB memory mapping/unmappings before each offline event.

--memhotplug-ops N

stop memhotplug stressors after N memory offline and online bogo operations.

--memrate N

start N workers that exercise a buffer with 1024, 512, 256, 128, 64, 32, 16 and 8 bit reads and writes. 1024, 512 and 256 reads and writes are available with compilers that support integer vectors. x86-64 cpus that support uncached (non-temporal "nt") writes also exercise 128, 64 and 32 writes providing higher write rates than the normal cached writes. x86-64 also exercises repeated string stores using 64, 32, 16 and 8 bit writes. CPUs that support prefetching reads also exercise 64 prefetched "pf" reads. This memory stressor allows one to also specify the maximum read and write rates. The stressors will run at maximum speed if no read or write rates are specified.

--memrate-bytes N

specify the size of the memory buffer being exercised. The default size is 256 MB. One can specify the size in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g, or cache sizes with L1, L2, L3 or LLC (lower level cache size).

--memrate-flush

flush cache between each memory exercising test to remove caching benefits in memory rate metrics.

--memrate-ops N

stop after N bogo memrate operations.

--memrate-rd-mbs N

specify the maximum allowed read rate in MB/sec. The actual read rate is dependent on scheduling jitter and memory accesses from other running processes.

--memrate-wr-mbs N

specify the maximum allowed read rate in MB/sec. The actual write rate is dependent on scheduling jitter and memory accesses from other running processes.

--memthrash N

start N workers that thrash and exercise a 16 MB buffer in various ways to try and trip thermal overrun. Each stressor will start 1 or more threads. The number of threads is chosen so that there will be at least 1 thread per CPU. Note that the optimal choice for N is a value that divides into the number of CPUs.

--memthrash-method method

specify a memthrash stress method. Available memthrash stress methods are described as follows:

Method	Description
all	iterate over all the below memthrash methods
chunk1	memset 1 byte chunks of random data into random locations
chunk8	memset 8 byte chunks of random data into random locations
chunk64	memset 64 byte chunks of random data into random locations
chunk256	memset 256 byte chunks of random data into random locations
chunkpage	memset page size chunks of random data into random locations
copy128	copy 128 byte chunks from chunk N + 1 to chunk N with streaming reads and writes with 128 bit memory accesses where possible.
flip	flip (invert) all bits in random locations
flush	flush cache line in random locations
lock	lock randomly choosing locations (Intel x86 and ARM CPUs only)
matrix	treat memory as a 2 × 2 matrix and swap random elements
memmove	copy all the data in buffer to the next memory location
memset	memset the memory with random data
memset64	memset the memory with a random 64 bit value in 64 byte chunks using non-temporal stores if possible or normal stores as a fallback
memsetstosd	memset the memory using x86 32 bit rep stosd instruction (x86 only)
mfence	stores with write serialization
numa	memory bind pages across numa nodes
prefetch	prefetch data at random memory locations
random	randomly run any of the memthrash methods except for 'random' and 'all'
reverse	swap 8 bit values from start to end and work towards the middle
spinread	spin loop read the same random location 2↑19 times
spinwrite	spin loop write the same random location 2↑19 times
swap	step through memory swapping bytes in steps of 65 and 129 byte strides
swap64	work through memory swapping adjacent 64 byte chunks
swapfwdrev	swap 64 bit values from start to end and work towards the middle and then from end to start and work towards the middle.
tlb	work through memory in sub-optimial strides of prime multiples of the cache line size with reads and then writes to cause Translation Lookaside Buffer (TLB) misses.

--memthrash-ops N

stop after N memthrash bogo operations.

--mergesort N

start N workers that sort 32 bit integers using the BSD mergesort.

--mergesort-method [ mergesort-libc | mergesort-nonlibc ]

select either the libc implementation of mergesort or an unoptimized implementation of mergesort. The default is the libc implementation if it is available.

--mergesort-ops N

stop mergesort stress workers after N bogo mergesorts.

--mergesort-size N

specify number of 32 bit integers to sort, default is 262144 (256 × 1024).

--metamix N

start N workers that generate a file metadata mix of operations. Each stressor runs 16 concurrent processes that each exercise a file's metadata with sequences of open, 256 lseeks and writes, fdatasync, close, fsync and then stat, open, 256 lseeks, reads, occasional file memory mapping, close, unlink and lstat.

--metamix-bytes N

set the size of metamix files, the default is 1 MB. One can specify the size as % of free space on the file system or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--metamix-ops N

stop the metamix stressor after N bogo metafile operations.

--mincore N

start N workers that walk through all of memory 1 page at a time checking if the page mapped and also is resident in memory using mincore(2). It also maps and unmaps a page to check if the page is mapped or not using mincore(2).

--mincore-ops N

stop after N mincore bogo operations. One mincore bogo op is equivalent to a 300 mincore(2) calls. --mincore-random instead of walking through pages sequentially, select pages at random. The chosen address is iterated over by shifting it right one place and checked by mincore until the address is less or equal to the page size.

--min-nanosleep N

start M workers that exercise nanosecond sleeps using powers of two nanosecond sleep delays. Once all the instances have completed, the minimum, maximum and mean sleep times are reported for the sleep delays across all the min-nanosleep stressor instances.

--min-nanosleep-ops N

stop after N rounds of measurements across all the sleeps are completed.

--min-nanosleep-max N

set the maximum nanosleep delay to use. If this is not a power of two then the previous power of two nanosecond delay time is used, e.g. specifying 10000 will select 8192 nanoseconds.

--min-nanosleep-sched [ batch | deadline | fifo | idle | other | rr ]

select scheduling policy. Note that deadline, fifo and rr require root privilege.

--misaligned N

start N workers that perform misaligned read and writes. By default, this will exercise 128 bit misaligned read and writes in 8 × 16 bits, 4 × 32 bits, 2 × 64 bits and 1 × 128 bits at the start of a page boundary, at the end of a page boundary and over a cache boundary. Misaligned read and writes operate at 1 byte offset from the natural alignment of the data type. On some architectures this can cause SIGBUS, SIGILL or SIGSEGV, these are handled and the misaligned stressor method causing the error is disabled.

--misaligned-method method

Available misaligned stress methods are described as follows:

Method	Description
all	iterate over all the following misaligned methods
int16rd	8 × 16 bit integer reads
int16wr	8 × 16 bit integer writes
int16inc	8 × 16 bit integer increments
int16atomic	8 × 16 bit atomic integer increments
int32rd	4 × 32 bit integer reads
int32wr	4 × 32 bit integer writes
int32wtnt	4 × 32 bit non-temporal stores (x86 only)
int32inc	4 × 32 bit integer increments
int32atomic	4 × 32 bit atomic integer increments
int64rd	2 × 64 bit integer reads
int64wr	2 × 64 bit integer writes
int64wtnt	4 × 64 bit non-temporal stores (x86 only)
int64inc	2 × 64 bit integer increments
int64atomic	2 × 64 bit atomic integer increments
int128rd	1 × 128 bit integer reads
int128wr	1 × 128 bit integer writes
int128inc	1 × 128 bit integer increments
int128atomic	1 × 128 bit atomic integer increments

Note that some of these options (128 bit integer and/or atomic operations) may not be available on some systems.

--misaligned-ops N

stop after N misaligned bogo operation. A misaligned bogo op is equivalent to 65536 × 128 bit reads or writes.

--mknod N

start N workers that create and remove fifos, empty files and named sockets using mknod and unlink.

--mknod-ops N

stop directory thrash workers after N bogo mknod operations.

--mlock N

start N workers that lock and unlock memory mapped pages using mlock(2), munlock(2), mlockall(2) and munlockall(2). This is achieved by the mapping of three contiguous pages and then locking the second page, hence ensuring non-contiguous pages are locked . This is then repeated until the maximum allowed mlocks or a maximum of 262144 mappings are made. Next, all future mappings are mlocked and the worker attempts to map 262144 pages, then all pages are munlocked and the pages are unmapped.

--mlock-ops N

stop after N mlock bogo operations.

--mlockmany N

start N workers that fork off a default of 1024 child processes in total; each child will attempt to anonymously mmap and mlock the maximum allowed mlockable memory size. The stress test attempts to avoid swapping by tracking low memory and swap allocations (but some swapping may occur). Once either the maximum number of child process is reached or all mlockable in-core memory is locked then child processes are killed and the stress test is repeated.

--mlockmany-ops N

stop after N mlockmany (mmap and mlock) operations.

--mlockmany-procs N

set the number of child processes to create per stressor. The default is to start a maximum of 1024 child processes in total across all the stressors. This option allows the setting of N child processes per stressor.

--mmap N

start N workers continuously calling mmap(2)/munmap(2). The initial mapping is a large chunk (size specified by --mmap-bytes) followed by pseudo-random 4 K unmappings, then pseudo-random 4 K mappings, and then linear 4 K unmappings. Note that this can cause systems to trip the kernel OOM killer on Linux systems if not enough physical memory and swap is not available. The MAP_POPULATE option is used to populate pages into memory on systems that support this. By default, anonymous mappings are used, however, the --mmap-file and --mmap-async options allow one to perform file based mappings if desired.

--mmap-async

enable file based memory mapping and use asynchronous msync'ing on each page, see --mmap-file.

--mmap-bytes N

allocate N bytes per mmap stress worker, the default is 256 MB. One can specify the size as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--mmap-file

enable file based memory mapping and by default use synchronous msync'ing on each page.

--mmap-madvise

enable randomized madvise(2) settings on pages.

--mmap-mergeable

mark pages as mergeable via madvise(2) where possible.

--mmap-mlock

attempt to mlock mmap'd pages into memory causing more memory pressure by preventing pages from swapped out.

--mmap-mmap2

use mmap2 for 4 K page aligned offsets if mmap2 is available, otherwise fall back to mmap.

--mmap-mprotect

change protection settings on each page of memory. Each time a page or a group of pages are mapped or remapped then this option will make the pages read-only, write-only, exec-only, and read-write.

--mmap-odirect

enable file based memory mapping and use O_DIRECT direct I/O.

--mmap-ops N

stop mmap stress workers after N bogo operations.

--mmap-osync

enable file based memory mapping and used O_SYNC synchronous I/O integrity completion.

--mmap-slow-munmap

enable page-by-page memory unmapping rather than attempting to memory unmap contiguous pages in one large unmapping. This can cause lock contention when running with many concurrent mmap stressors and will slow down the stressor.

--mmap-stressful

enable --mmap-file, --mmap-madvise, --mmap-mergeable, --mmap-mlock, --mmap-mprotect, --mmap-odirect, --mmap-slow-munmap

--mmap-write-check

write into each page a unique 64 bit check value for all pages and then read the value for a sanity check. This will force newly memory mapped pages to be faulted-in which slows down mmap bogo-op rate. This can also cause lock contention on page allocation and page unmapping on systems with many CPU threads and with cgroup memory accounting.

--mmapaddr N

start N workers that memory map pages at a random memory location that is not already mapped. On 64 bit machines the random address is randomly chosen 32 bit or 64 bit address. If the mapping works a second page is memory mapped from the first mapped address. The stressor exercises mmap/munmap, mincore and segfault handling.

--mmapaddr-mlock

attempt to mlock mmap'd pages into memory causing more memory pressure by preventing pages from swapped out.

--mmapaddr-ops N

stop after N random address mmap bogo operations.

--mmapfork N

start N workers that each fork off 32 child processes, each of which tries to allocate some of the free memory left in the system (and trying to avoid any swapping). The child processes then hint that the allocation will be needed with madvise(2) and then memset it to zero and hint that it is no longer needed with madvise before exiting. This produces significant amounts of VM activity, a lot of cache misses and with minimal swapping.

--mmapfork-bytes N

specify the size of memory mapped fork region size. One can specify the size in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--mmapfork-ops N

stop after N mmapfork bogo operations.

--mmapfiles N

start N workers that attempt to memory map and then unmap up to 512 × 1024 files into memory. The stressor will traverse /lib, /lib32, /lib64, /boot, /bin, /etc, /sbin, /usr, /var, /sys and /proc and attempt to memory map files in these directories. Note that mapping bogo-ops rate will depend on the speed of access to files on these file systems.

--mmapfiles-ops N

stop after N memory map/unmap operations.

--mmapfiles-populate

The default is to perform a memory mapping and not fault any pages into physical memory. This option uses MAP_POPULATE when available and will also read the first byte in each page to ensure pages are faulted into memory to force memory population from file.

--mmapfiles-shared

The default is for private memory mapped files, however, with this option will use shared memory mappings.

--mmapfixed N

start N workers that perform fixed address allocations from the top virtual address down to 128 K. The allocated sizes are from 1 page to 8 pages and various random mmap flags are used MAP_SHARED/MAP_PRIVATE, MAP_LOCKED, MAP_NORESERVE, MAP_POPULATE. If successfully map'd then the allocation is remap'd first to a large range of addresses based on a random start and finally an address that is several pages higher in memory. Mappings and remappings are madvised with random madvise options to further exercise the mappings.

--mmapfixed-mlock

attempt to mlock mmap'd pages into memory causing more memory pressure by preventing pages from swapped out.

--mmapfixed-ops N

stop after N mmapfixed memory mapping bogo operations.

--mmaphuge N

start N workers that attempt to mmap a set of huge pages and large huge page sized mappings. Successful mappings are madvised with MADV_NOHUGEPAGE and MADV_HUGEPAGE settings and then 1/64th of the normal small page size pages are touched. Finally, an attempt to unmap a small page size page at the end of the mapping is made (these may fail on huge pages) before the set of pages are unmapped. By default 8192 mappings are attempted per round of mappings or until swapping is detected.

--mmaphuge-file

attempt to mmap on a 16 MB temporary file and random 4 K offsets. If this fails, anonymous mappings are used instead.

--mmaphuge-mlock

attempt to mlock mmap'd huge pages into memory causing more memory pressure by preventing pages from swapped out.

--mmaphuge-mmaps N

set the number of huge page mappings to attempt in each round of mappings. The default is 8192 mappings.

--mmaphuge-ops N

stop after N mmaphuge bogo operations

--mmapmany N

start N workers that attempt to create the maximum allowed per-process memory mappings. This is achieved by mapping 3 contiguous pages and then unmapping the middle page hence splitting the mapping into two. This is then repeated until the maximum allowed mappings or a maximum of 262144 mappings are made.

--mmapmany-mlock

attempt to mlock mmap'd huge pages into memory causing more memory pressure by preventing pages from swapped out.

--mmapmany-ops N

stop after N mmapmany bogo operations

--module N

start N workers that use finit_module() to load the module specified or the hello test module, if is available. There are different ways to test loading modules. Using modprobe calls in a loop, using the kernel kernel module autoloader, and this stress-ng module stressor. To stress tests modprobe we can simply run the userspace modprobe program in a loop. To stress test the kernel module autoloader we can stress tests using the upstream kernel tools/testing/selftests/kmod/kmod.sh. This ends up calling modprobe in the end, and it has its own caps built-in to self protect the kernel from too many requests at the same time. The userspace modprobe call will also prevent calls if the same module exists already. The stress-ng modules stressor is designed to help stress test the finit_module() system call even if the module is already loaded, testing races that are otherwise hard to reproduce.

--module-name NAME

NAME of the module to use, for example: test_module, xfs, ext4. By default test_module is used so CONFIG_TEST_LKM must be enabled in the kernel. The module dependencies must be loaded prior to running these stressor tests, as this stresses running finit_module() not using modprobe.

--module-no-modver

ignore module modversions when using finit_module().

--module-no-vermag

ignore module versions when using finit_module().

--module-no-unload

do not unload the module right after loading it with finit_module().

--module-ops N

stop after N module load/unload cycles

--monte-carlo N

start N stressors that compute π and e (Euler's number) using Monte Carlo computational experiments with various random number generators.

--monte-carlo-method [ all | e | exp | pi | sin | sqrt | squircle ]

specify the computation to perform, options are as follows:

Method	Description
all	use all monte carlo computation methods
e	compute Euler's constant e
exp	integrate exp(x ↑ 2) for x = 0..1
pi	compute π from the area of a circle
sin	integrate sin(x) for x = 0..π
sqrt	integrate sqrt(1 + x ↑ 4) for x = 0..1
squircle	area of a unit squircle x ↑ 4 + y ↑ 4 = 1

--monte-carlo-ops N

stop after Monte Carlo computation experiments

--monte-carlo-rand [ all | drand48 | getrandom | lcg | pcg32 | mwc64 | random | xorshift ]

specify the random number generator to use, options are as follows:

Method	Description
all	use all the random number generators
arc4	use the libc cryptographically-secure pseudorandom arc4random(3) number generator.
drand48	use the libc linear congruential algorithm drand48(3) using 48-bit integer arithmetic.
getrandom	use the getrandom(2) system call for random values.
lcg	use a 32 bit Paker-Miller Linear Congruential Generator, with a division optimization.
pcg32	use a 32 bit O'Neill Permuted Congruential Generator.
mwc64	use the 64 bit stress-ng Multiply With Carry random number generator.
random	use the libc random(3) Non-linear Additive Feedback random number generator.
xorshift	use a 32 bit Marsaglia shift-register random number generator.

--monte-carlo-samples N

specify the number of random number samples to use to compute π or e, default is 100000.

--mpfr N

start N workers that exercise multi-precision floating point operations using the GNU Multi-Precision Floating Point Reliable library (mpfr). Operations computed are as follows:

Method	Description
apery	calculate Apery's constant ζ(3); the sum of 1/(n ↑ 3).
cosine	compute cos(θ) for θ = 0 to 2π in 100 steps.
euler	compute e using n = (1 + (1 ÷ n)) ↑ n.
exp	compute 1000 exponentials.
log	computer 1000 natural logarithms.
omega	compute the omega constant defined by Ωe↑Ω = 1 using efficient iteration of Ωn+1 = (1 + Ωn) / (1 + e↑Ωn).
phi	compute the Golden Ratio ϕ using series.
sine	compute sin(θ) for θ = 0 to 2π in 100 steps.
nsqrt	compute square root using Newton-Raphson.

--mpfr-ops N

stop workers after N iterations of various multi-precision floating point operations.

--mpfr-precision N

specify the precision in binary digits of the floating point operations. The default is 1000 bits, the allowed range is 32 to 1000000 (very slow).

--mprotect N

start N workers that exercise changing page protection settings and access memory after each change. 8 processes per worker contend with each other changing page proection settings on a shared memory region of just a few pages to cause TLB flushes. A read and write to the pages can cause segmentation faults and these are handled by the stressor. All combinations of page protection settings are exercised including invalid combinations.

--mprotect-ops N

stop after N mprotect calls.

--mq N

start N sender and receiver processes that continually send and receive messages using POSIX message queues. (Linux only).

--mq-ops N

stop after N bogo POSIX message send operations completed.

--mq-size N

specify size of POSIX message queue. The default size is 10 messages and most Linux systems this is the maximum allowed size for normal users. If the given size is greater than the allowed message queue size then a warning is issued and the maximum allowed size is used instead.

--mremap N

start N workers continuously calling mmap(2), mremap(2) and munmap(2). The initial anonymous mapping is a large chunk (size specified by --mremap-bytes) and then iteratively halved in size by remapping all the way down to a page size and then back up to the original size. This worker is only available for Linux.

--mremap-bytes N

initially allocate N bytes per remap stress worker, the default is 256 MB. One can specify the size in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--mremap-mlock

attempt to mlock remap'd pages into memory causing more memory pressure by preventing pages from swapped out.

--mremap-ops N

stop mremap stress workers after N bogo operations.

--mseal N

start N memory sealing stressors that exercise madvise, mremap, mprotect and mseal operations on two pages of of memory mapped anonymous private memory. Linux 6.10+ kernels only.

--mseal-ops N

stop after N msealed memory operations.

--msg N

start N sender and receiver processes that continually send and receive messages using System V message IPC.

--msg-bytes N

specify the size of the message being sent and received. Range 4 to 8192 bytes, default is 4 bytes.

--msg-ops N

stop after N bogo message send operations completed.

--msg-types N

select the quality of message types (mtype) to use. By default, msgsnd sends messages with a mtype of 1, this option allows one to send messages types in the range 1..N to exercise the message queue receive ordering. This will also impact throughput performance.

--msync N

start N stressors that msync data from a file backed memory mapping from memory back to the file and msync modified data from the file back to the mapped memory. This exercises the msync(2) MS_SYNC and MS_INVALIDATE sync operations.

--msync-bytes N

allocate N bytes for the memory mapped file, the default is 256 MB. One can specify the size as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--msync-ops N

stop after N msync bogo operations completed.

--msyncmany N

start N stressors that memory map up to 32768 pages on the same page of a temporary file, change the first 32 bits in a page and msync the data back to the file. The other 32767 pages are examined to see if the 32 bit check value is msync'd back to these pages.

--msyncmany-ops N

stop after N msync calls in the msyncmany stressors are completed.

--mtx N

start N stressors that exercise ISO C mutex locking and unlocking.

--mtx-ops N

stop after N bogo mutex lock/unlock operations.

--mtx-procs N

By default 2 threads are used for locking/unlocking on a single mutex. This option allows the default to be changed to 2 to 64 concurrent threads.

--munmap N

start N stressors that exercise unmapping of shared non-executable mapped regions of child processes (Linux only). The unmappings map shared memory regions page by page with a prime sized stride that creates many temporary mapping holes. One the unmappings are complete the child will exit and a new one is started. Note that this may trigger segmentation faults in the child process, these are handled where possible by forcing the child process to call _exit(2).

--munmap-ops N

stop after N page unmappings.

--mutex N

start N stressors that exercise pthread mutex locking and unlocking. If run with enough privilege then the FIFO scheduler is used and a random priority between 0 and 80% of the maximum FIFO priority level is selected for the locking operation. The minimum FIFO priority level is selected for the critical mutex section and unlocking operation to exercise random inverted priority scheduling.

--mutex-affinity

enable random CPU affinity changing between mutex lock and unlock.

--mutex-ops N

stop after N bogo mutex lock/unlock operations.

--mutex-procs N

By default 2 threads are used for locking/unlocking on a single mutex. This option allows the default to be changed to 2 to 64 concurrent threads.

--nanosleep N

start N workers that each run pthreads that call nanosleep with random delays from 1 to 2↑18 nanoseconds. This should exercise the high resolution timers and scheduler.

--nanosleep-method [ all | cstate | random | ns | us | ms ]

select the nanosleep sleep duration method. By default, cstate residency durations (if they exist) and random durations are used. This option allows one to select one of the three methods:

Method	Description
all	use cstate and random nanosecond durations.
cstate	use cstate nanosecond durations. It is recommended to also use --nanosleep-threads 1 to exercise less conconcurrent nanosleeps to allow CPUs to drop into deep C states.
random	use random nanosecond durations between 1 and 2^18 nanoseconds.
ns	use 1ns (nanosecond) nanosleeps
us	use 1us (microsecond) nanosleeps
ms	use 1ms (millisecond) nanosleeps

--nanosleep-ops N

stop the nanosleep stressor after N bogo nanosleep operations.

--nanosleep-threads N

specify the number of concurrent pthreads to run per stressor. The default is 8 and the allowed range is 1 to 1024.

--netdev N

start N workers that exercise various netdevice ioctl commands across all the available network devices. The ioctls exercised by this stressor are as follows: SIOCGIFCONF, SIOCGIFINDEX, SIOCGIFNAME, SIOCGIFFLAGS, SIOCGIFADDR, SIOCGIFNETMASK, SIOCGIFMETRIC, SIOCGIFMTU, SIOCGIFHWADDR, SIOCGIFMAP and SIOCGIFTXQLEN. See netdevice(7) for more details of these ioctl commands.

--netdev-ops N

stop after N netdev bogo operations completed.

--netlink-proc N

start N workers that spawn child processes and monitor fork/exec/exit process events via the proc netlink connector. Each event received is counted as a bogo op. This stressor can only be run on Linux and requires CAP_NET_ADMIN capability.

--netlink-proc-ops N

stop the proc netlink connector stressors after N bogo ops.

--netlink-task N

start N workers that collect task statistics via the netlink taskstats interface. This stressor can only be run on Linux and requires CAP_NET_ADMIN capability.

--netlink-task-ops N

stop the taskstats netlink connector stressors after N bogo ops.

--nice N

start N cpu consuming workers that exercise the available nice levels. Each iteration forks off a child process that runs through the all the nice levels running a busy loop for 0.1 seconds per level and then exits.

--nice-ops N

stop after N nice bogo nice loops

--nop N

start N workers that consume cpu cycles issuing no-op instructions. This stressor is available if the assembler supports the "nop" instruction.

--nop-instr INSTR

use alternative nop instruction INSTR. For x86 CPUs INSTR can be one of nop, pause, nop2 (2 byte nop) through to nop15 (15 byte nop). For ARM CPUs, INSTR can be one of nop or yield. For PPC64 CPUs, INSTR can be one of nop, mdoio, mdoom or yield. For S390 CPUs, INSTR can be one of nop or nopr. For other processors, INSTR is only nop. The random INSTR option selects a randon mix of the available nop instructions. If the chosen INSTR generates an SIGILL signal, then the stressor falls back to the vanilla nop instruction.

--nop-ops N

stop nop workers after N no-op bogo operations. Each bogo-operation is equivalent to 256 loops of 256 no-op instructions.

--null N

start N workers that exercise /dev/null with writes, lseek, ioctl, fcntl, fallocate and fdatasync. For just /dev/null write benchmarking use the --null-write option.

--null-ops N

stop null stress workers after N /dev/null bogo operations.

--null-write

just write to /dev/null with 4 K writes with no additional exercising on /dev/null.

--numa N

start N workers that migrate stressors and a 4 MB memory mapped buffer around all the available NUMA nodes. This uses migrate_pages(2) to move the stressors and mbind(2) and move_pages(2) to move the pages of the mapped buffer. After each move, the buffer is written to force activity over the bus which results cache misses. This test will only run on hardware with NUMA enabled and more than 1 NUMA node.

--numa-bytes N

specify the total number bytes to be exercised by all the workers, the given size is divided by the number of workers and rounded to the nearest page size. The default is 4 MB per worker. One can specify the size as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--numa-ops N

stop NUMA stress workers after N bogo NUMA operations.

--numa-shuffle-addr

shuffle page order for the address list when calling move_pages(2)

--numa-shuffle-node

shuffle node order for the address list when calling move_pages(2)

--oom-pipe N

start N workers that create as many pipes as allowed and exercise expanding and shrinking the pipes from the largest pipe size down to a page size. Data is written into the pipes and read out again to fill the pipe buffers. With the --aggressive mode enabled the data is not read out when the pipes are shrunk, causing the kernel to OOM processes aggressively. Running many instances of this stressor will force kernel to OOM processes due to the many large pipe buffer allocations.

--oom-pipe-ops N

stop after N bogo pipe expand/shrink operations.

--opcode N

start N workers that fork off children that execute randomly generated executable code. This will generate issues such as illegal instructions, bus errors, segmentation faults, traps, floating point errors that are handled gracefully by the stressor.

--opcode-method [ inc | mixed | random | text ]

select the opcode generation method. By default, random bytes are used to generate the executable code. This option allows one to select one of the three methods:

Method	Description
inc	use incrementing 32 bit opcode patterns from 0x00000000 to 0xfffffff inclusive.
mixed	use a mix of incrementing 32 bit opcode patterns and random 32 bit opcode patterns that are also inverted, encoded with gray encoding and bit reversed.
random	generate opcodes using random bytes from a mwc random generator.
text	copies random chunks of code from the stress-ng text segment and randomly flips single bits in a random choice of 1/8th of the code.

--opcode-ops N

stop after N attempts to execute illegal code.

-o N, --open N

start N workers that perform open(2) and then close(2) operations on /dev/zero. The maximum opens at one time is system defined, so the test will run up to this maximum, or 65536 open file descriptors, which ever comes first.

--open-fd

run a child process that scans /proc/$PID/fd and attempts to open the files that the stressor has opened. This exercises racing open/close operations on the proc interface.

--open-max N

try to open a maximum of N files (or up to the maximum per-process open file system limit). The value can be the number of files or a percentage of the maximum per-process open file system limit.

--open-ops N

stop the open stress workers after N bogo open operations.

--pagemove N

start N workers that mmap a memory region (default 4 MB) and then shuffle pages to the virtual address of the previous page. Each page shuffle uses 3 mremap operations to move a page. This exercises page tables and Translation Lookaside Buffer (TLB) flushing.

--pagemove-bytes

specify the size of the memory mapped region to be exercised. One can specify the size as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--pagemove-mlock

attempt to mlock mmap'd and mremap'd pages into memory causing more memory pressure by preventing pages from swapped out.

--pagemove-ops N

stop after N pagemove shuffling operations, where suffling all the pages in the mmap'd region is equivalent to 1 bogo-operation.

--pageswap N

start N workers that exercise page swap in and swap out. Pages are allocated and paged out using madvise MADV_PAGEOUT. One the maximum per process number of mmaps are reached or 65536 pages are allocated the pages are read to page them back in and unmapped in reverse mapping order.

--pageswap-ops N

stop after N page allocation bogo operations.

--pci N

exercise PCI sysfs by running N workers that read data (and mmap/unmap PCI config or PCI resource files). Linux only. Running as root will allow config and resource mmappings to be read and exercises PCI I/O mapping.

--pci-dev xxxx:xx:xx.x

specify a PCI device to exercise rather than exercise all PCI devices. The device is specified using the PCI device name xxxx:xx:xx.x where x is a hexadecimal digit.

--pci-ops N

stop pci stress workers after N PCI subdirectory exercising operations.

--personality N

start N workers that attempt to set personality and get all the available personality types (process execution domain types) via the personality(2) system call. (Linux only).

--personality-ops N

stop personality stress workers after N bogo personality operations.

--peterson N

start N workers that exercises mutex exclusion between two processes using shared memory with the Peterson Algorithm. Where possible this uses memory fencing and falls back to using GCC __sync_synchronize if they are not available. The stressors contain simple mutex and memory coherency sanity checks.

--peterson-ops N

stop peterson workers after N mutex operations.

--physpage N

start N workers that use /proc/self/pagemap and /proc/kpagecount to determine the physical page and page count of a virtual mapped page and a page that is shared among all the stressors. Linux only and requires the CAP_SYS_ADMIN capabilities.

--physpage-mtrr

enable setting various memory type rage register (MTRR) types on physical pages (Linux and x86 only).

--physpage-ops N

stop physpage stress workers after N bogo physical address lookups.

--pidfd N

start N workers that exercise signal sending via the pidfd_send_signal system call. This stressor creates child processes and checks if they exist and can be stopped, restarted and killed using the pidfd_send_signal system call.

--pidfd-ops N

stop pidfd stress workers after N child processes have been created, tested and killed with pidfd_send_signal.

--ping-sock N

start N workers that send small randomized ICMP messages to the localhost across a range of ports (1024..65535) using a "ping" socket with an AF_INET domain, a SOCK_DGRAM socket type and an IPPROTO_ICMP protocol.

--ping-sock-ops N

stop the ping-sock stress workers after N ICMP messages are sent.

-p N, --pipe N

start N workers that perform large pipe writes and reads to exercise pipe I/O. This exercises memory write and reads as well as context switching. Each worker has two processes, a reader and a writer.

--pipe-data-size N

specifies the size in bytes of each write to the pipe (range from 4 bytes to 4096 bytes). Setting a small data size will cause more writes to be buffered in the pipe, hence reducing the context switch rate between the pipe writer and pipe reader processes. Default size is the page size.

--pipe-ops N

stop pipe stress workers after N bogo pipe write operations.

--pipe-vmsplice

use vmsplice(2) to splice data pages to/from pipe. Requires pipe packet mode using O_DIRECT and buffer twice the size of the pipe to ensure verification data sequences.

--pipe-size N

specifies the size of the pipe in bytes (for systems that support the F_SETPIPE_SZ fcntl() command). Setting a small pipe size will cause the pipe to fill and block more frequently, hence increasing the context switch rate between the pipe writer and the pipe reader processes. As of version 0.15.11 the default size is 4096 bytes.

--pipeherd N

start N workers that pass a 64 bit token counter to/from 100 child processes over a shared pipe. This forces a high context switch rate and can trigger a "thundering herd" of wakeups on processes that are blocked on pipe waits.

--pipeherd-ops N

stop pipe stress workers after N bogo pipe write operations.

--pipeherd-yield

force a scheduling yield after each write, this increases the context switch rate.

--pkey N

start N workers that change memory protection using a protection key (pkey) and the pkey_mprotect call (Linux only). This will try to allocate a pkey and use this for the page protection, however, if this fails then the special pkey -1 will be used (and the kernel will use the normal mprotect mechanism instead). Various page protection mixes of read/write/exec/none will be cycled through on randomly chosen pre-allocated pages.

--pkey-ops N

stop after N pkey_mprotect page protection cycles.

--plugin N

start N workers that run user provided stressor functions loaded from a shared library. The shared library can contain one or more stressor functions prefixed with stress_ in their name. By default the plugin stressor will find all functions prefixed with stress_ in their name and exercise these one by one in a round-robin loop, but a specific stressor can be selected using the --plugin-method option. The stressor function takes no parameters and returns 0 for success and non-zero for failure (and will terminate the plugin stressor). Each time a stressor function is executed the bogo-op counter is incremented by one. The following example performs 10,000 nop instructions per bogo-op:

int stress_example(void)
{
        int i;
        for (i = 0; i < 10000; i++) {
                __asm__ __volatile__("nop");
        }
        return 0;  /* Success */
}

gcc -fpic -shared -o example.so example.c

stress-ng --plugin 1 --plugin-so ./example.so

--plugin-method function

run a specific stressor function, specify the name without the leading stress_ prefix.

--plugin-ops N

stop after N iterations of the user provided stressor function(s).

--plugin-so name

specify the shared library containing the user provided stressor function(s).

-P N, --poll N

start N workers that perform zero timeout polling via the poll(2), ppoll(2), select(2), pselect(2) and sleep(3) calls. This wastes system and user time doing nothing.

--poll-fds N

specify the number of file descriptors to poll/ppoll/select/pselect on. The maximum number for select/pselect is limited by FD_SETSIZE and the upper maximum is also limited by the maximum number of pipe open descriptors allowed.

--poll-ops N

stop poll stress workers after N bogo poll operations.

--powmath N

start N workers that exercise various power functions with input values 0 to 1 in steps of 0.001; the results are sanity checked to ensure no variation occurs after each round of 10000 computations.

--powmath-ops N

stop after N power function bogo-operation loops.

--powmath-method method

specify a power function to exercise. Available power function stress methods are described as follows:

Method	Description
all	iterate over all the below power functions methods
cpow	complex double power function
cpowf	complex float power function
cpowl	complex long double power function
csqrt	complex double square root function (1/2 power)
csqrtf	complex float square root function (1/2 power)
csqrtl	complex long double square root function (1/2 power)
cbrt	double cube root function (1/3 power)
cbrtf	float cube root function (1/3 power)
cbrtl	long double cube root function (1/3 power)
hypot	double Euclidean distance function (hypotenuse)
hypotf	float Euclidean distance function (hypotenuse)
hypotl	long double Euclidean distance function (hypotenuse)
pow	double power function
powf	float power function
powl	long double power function
sqrt	double square root function (1/2 power)
sqrtf	float square root function (1/2 power)
sqrtl	long double square root function (1/2 power)

--prctl N

start N workers that exercise the majority of the prctl(2) system call options. Each batch of prctl calls is performed inside a new child process to ensure the limit of prctl is contained inside a new process every time. Some prctl options are architecture specific, however, this stressor will exercise these even if they are not implemented.

--prctl-ops N

stop prctl workers after N batches of prctl calls

--prefetch N

start N workers that benchmark prefetch and non-prefetch reads of a L3 cache sized buffer. The buffer is read with loops of 8 × 64 bit reads per iteration. In the prefetch cases, data is prefetched ahead of the current read position by various sized offsets, from 64 bytes to 8 K to find the best memory read throughput. The stressor reports the non-prefetch read rate and the best prefetched read rate. It also reports the prefetch offset and an estimate of the amount of time between the prefetch issue and the actual memory read operation. These statistics will vary from run-to-run due to system noise and CPU frequency scaling.

--prefetch-l3-size N

specify the size of the l3 cache

--prefetch-method N

select the prefetching method. Available methods are:

Method	Description
builtin	Use the __builtin_prefetch(3) function for prefetching. This is the default.
builtinl0	Use the __builtin_prefetch(3) function for prefetching, with a locality 0 hint.
builtinl3	Use the __builtin_prefetch(3) function for prefetching, with a locality 3 hint.
dcbt	Use the ppc64 dcbt instruction to fetch data into the L1 cache (ppc64 only).
dcbtst	Use the ppc64 dcbtst instruction to fetch data into the L1 cache (ppc64 only).
prefetcht0	Use the x86 prefetcht0 instruction to prefetch data into all levels of the cache hierarchy (x86 only).
prefetcht1	Use the x86 prefetcht1 instruction (temporal data with respect to first level cache) to prefetch data into level 2 cache and higher (x86 only).
prefetcht2	Use the x86 prefetcht2 instruction (temporal data with respect to second level cache) to prefetch data into level 2 cache and higher (x86 only).
prefetchnta	Use the x86 prefetchnta instruction (non-temporal data with respect to all cache levels) into a location close to the processor, minimizing cache pollution (x86 only).

--prefetch-ops N

stop prefetch stressors after N benchmark operations

--prime N

start N workers that find prime numbers using the GNU Multiple Precision Arithmetic Library for large integers. The GMP mpz_nextprime function is used to find primes and it uses a probabilistic algorithm to identify primes, but there is a extremely small chance that the values found are non-prime. The search becomes computationally more expensive over time to find larger and larger primes, hence the bogo-op rate will reduce over time.

--prime-method [ factorial | inc | pwr2 | pwr10 ]

selects the method of calculating the next value from where to start searching primes and hence how large the primes get. The default is inc, the methods to start searching for primes are described as follows.

Method	Description
factorial	start of search based on factorial expansion. This grows rapidly.
inc	start of search based on increments by 2. This grows very slowly.
pwr2	start of search based on powers of 2. Grows relatively quicky.
pwr10	start of search based on powers of 10. Grows by 1 digit per iteration and grows quickly.

--prime-ops N

stop after finding N prime numbers.

--prime-progress

show the number of primes found and length of largest prime found. This is displayed either every 60 seconds or more than 60 seconds if it takes longer to find the next prime.

--prime-start N

start the prime search from value N. The value may be expressed as an integer value or as a floating point value (e.g. 1e200 to express a very large starting value).

--prio-inv N

start N workers that exercise mutex lock priority inversion scheduling. Three child process run with low, medium and high FIFO scheduling priorities. The processes with low and high priorities share a mutex lock that both try to lock and unlock, aiming to make the low priority process block the high priority process. Meanwhile the middle priority process will run in priority over the low priority process, causing the high priority process to become unrunnable.

--prio-inv-ops N

stop after N bogo lock/unlock operations.

--prio-inv-type [ inherit | none | protect ]

select the mutex lock priority inversion type, described as follows:

Type	Description
inherit	The priority of the process owning the mutex lock is run with highest priority of any other process waiting on the lock to avoid priority inversion deadlock.
none	The priority of the process owning the mutex lock is not affected by its mutex ownership. This may lead to the high priority process to become unrunnable on a single thread system.
protect	The priority of the process owning the mutex lock is given the priority of the mutex (in this stress test case, the maximum priority) during the lock ownership.

--prio-inv-policy [ batch | idle | fifo | other | rr ]

select the scheduling policy. "Normal" policies (batch, idle and other) can be selected as an unprivileged user, however "Real Time" policies (fifo and rr) can only be selected with the appropriate privilege. By default "rr" is selected but will it fall back to "other" for unprivileged users.

--priv-instr N

start N workers that exercise various architecture specific privileged instructions that cannot be executed by userspace programs. These instructions will be trapped and processed by SIGSEGV or SIGILL signal handlers.

--priv-instr-ops N

stop priv-instr stressors after N rounds of executing privileged instructions.

--procfs N

start N workers that read files from /proc and recursively read files from /proc/self (Linux only).

--procfs-ops N

stop procfs reading after N bogo read operations. Note, since the number of entries may vary between kernels, this bogo ops metric is probably very misleading.

--pseek N

start N workers that exercise pwrite() and pread() with lseek() positioning tests. Each worker has 4 sub-processes that perform repeated pwrite() and pread() operations using the same shared file descriptor. Two of the processes are started using pthreads (if available), another two processes are started with fork(). Using pwrite() and pread() should perform I/O without altering the shared file descriptor file offset. The main worker process performs I/O using lseek()/write() and lseek()/read() calls that change the file offset; lseeks are sanity checked to see if they are being altered by pwrite() and pread() calls.

--pseek-io-size N

specify size of each write/read I/O operation in bytes. Size can be from 1 byte to 1 MB.

--pseek-ops N

stop after N writes by the main worker process.

--pseek-rand

normally each sub-process writes to a fix file offset, using this option will randomize the offset on each write/read cycle.

--pthread N

start N workers that iteratively creates and terminates multiple pthreads (the default is 1024 pthreads per worker). In each iteration, each newly created pthread waits until the worker has created all the pthreads and then they all terminate together.

--pthread-max N

create N pthreads per worker. If the product of the number of pthreads by the number of workers is greater than the soft limit of allowed pthreads then the maximum is re-adjusted down to the maximum allowed.

--pthread-ops N

stop pthread workers after N bogo pthread create operations.

--ptrace N

start N workers that fork and trace system calls of a child process using ptrace(2).

--ptrace-ops N

stop ptracer workers after N bogo system calls are traced.

--ptr-chase N

start N workers that chase memory pointers around page sized nodes of pointers. By default each stressor instance allocates 4096 pages of nodes, each node is an array of pointers that are randomly set to point to other node pages. The stressors follow randomly chosen pointers from each node, chasing around the entire node space. This exercises pointer fetching, pointer dereferencing and is a cache-read exercising stressor. The nodes are allocated with 50% of pages from the heap and 50% from mmap'd memory.

--ptr-chase-ops N

stop after N pointer chases

--ptr-chase-pages N

select number of pages to allocate for the nodes.

--pty N

start N workers that repeatedly attempt to open pseudoterminals and perform various pty ioctls upon the ptys before closing them.

--pty-max N

try to open a maximum of N pseudoterminals, the default is 65536. The allowed range of this setting is 8..65536.

--pty-ops N

stop pty workers after N pty bogo operations.

-Q, --qsort N

start N workers that sort 32 bit integers using qsort.

--qsort-method [ qsort-libc | qsort-bm ]

select either the libc implementation of qsort or the J. L. Bentley and M. D. McIlroy implementation of qsort. The default is the libc implementation.

--qsort-ops N

stop qsort stress workers after N bogo qsorts.

--qsort-size N

specify number of 32 bit integers to sort, default is 262144 (256 × 1024).

--quota N

start N workers that exercise the Q_GETQUOTA, Q_GETFMT, Q_GETINFO, Q_GETSTATS and Q_SYNC quotactl(2) commands on all the available mounted block based file systems. Requires CAP_SYS_ADMIN capability to run.

--quota-ops N

stop quota stress workers after N bogo quotactl operations.

--race-sched N

start N workers that exercise rapid changing CPU affinity child processes both from the controlling stressor and by the child processes. Child processes are created and terminated rapidly with the aim to create race conditions where affinity changing occurs during process run states.

--race-sched-method [ all | next | prev | rand | randinc | syncnext | syncprev ]

Select the method moving a process to a specific CPU. Available methods are described as follows:

Method	Description
all	iterate over all the race-sched methods as listed below:
next	move a process to the next CPU, wrap around to zero when maximum CPU is reached.
prev	move a process to the previous CPU, wrap around to the maximum CPU when the first CPU is reached.
rand	move a process to any randomly chosen CPU.
randinc	move a process to the current CPU + a randomly chosen value 1..4, modulo the number of CPUs.
syncnext	move synchronously all the race-sched stressor processes to the next CPU every second; this loads just 1 CPU at a time in a round-robin method.
syncprev	move synchronously all the race-sched stressor processes to the previous CPU every second; this loads just 1 CPU at a time in a round-robin method.

--race-sched-ops N

stop after N process creation bogo-operations.

--radixsort N

start N workers that sort random 8 byte strings using radixsort.

--radixsort-method [ radixsort-libc | radixsort-nonlibc ]

select either the libc implementation of radixsort or an optimized implementation of radixsort. The default is the libc implementation if it is available.

--radixsort-ops N

stop radixsort stress workers after N bogo radixsorts.

--radixsort-size N

specify number of strings to sort, default is 262144 (256 × 1024).

--ramfs N

start N workers mounting a memory based file system using ramfs and tmpfs (Linux only). This alternates between mounting and umounting a ramfs or tmpfs file system using the traditional mount(2) and umount(2) system call as well as the newer Linux 5.2 fsopen(2), fsmount(2), fsconfig(2) and move_mount(2) system calls if they are available. The default ram file system size is 2 MB.

--ramfs-fill

fill ramfs with zero'd data using fallocate(2) if it is available or multiple calls to write(2) if not.

--ramfs-ops N

stop after N ramfs mount operations.

--ramfs-size N

set the ramfs size (must be multiples of the page size).

--rawdev N

start N workers that read the underlying raw drive device using direct IO reads. The device (with minor number 0) that stores the current working directory is the raw device to be read by the stressor. The read size is exactly the size of the underlying device block size. By default, this stressor will exercise all the of the rawdev methods (see the --rawdev-method option). This is a Linux only stressor and requires root privilege to be able to read the raw device.

--rawdev-method method

Available rawdev stress methods are described as follows:

Method	Description
all	iterate over all the rawdev stress methods as listed below:
sweep	repeatedly read across the raw device from the 0th block to the end block in steps of the number of blocks on the device / 128 and back to the start again.
wiggle	repeatedly read across the raw device in 128 evenly steps with each step reading 1024 blocks backwards from each step.
ends	repeatedly read the first and last 128 start and end blocks of the raw device alternating from start of the device to the end of the device.
random	repeatedly read 256 random blocks
burst	repeatedly read 256 sequential blocks starting from a random block on the raw device.

--rawdev-ops N

stop the rawdev stress workers after N raw device read bogo operations.

--randlist N

start N workers that creates a list of objects in randomized memory order and traverses the list setting and reading the objects. This is designed to exerise memory and cache thrashing. Normally the objects are allocated on the heap, however for objects of page size or larger there is a 1 in 16 chance of objects being allocated using shared anonymous memory mapping to mix up the address spaces of the allocations to create more TLB thrashing.

--randist-compact

Allocate all the list objects using one large heap allocation and divide this up for all the list objects. This removes the overhead of the heap keeping track of each list object, hence uses less memory.

--randlist-items N

Allocate N items on the list. By default, 100,000 items are allocated.

--randlist-ops N

stop randlist workers after N list traversals

--randlist-size N

Allocate each item to be N bytes in size. By default, the size is 64 bytes of data payload plus the list handling pointer overhead.

--rawsock N

start N workers that send and receive packet data using raw sockets on the localhost. Requires CAP_NET_RAW to run.

--rawsock-ops N

stop rawsock workers after N packets are received.

--rawsock-port P

start at socket port P. For N rawsock worker processes, ports P to P - 1 are used.

--rawpkt N

start N workers that sends and receives ethernet packets using raw packets on the localhost via the loopback device. Requires CAP_NET_RAW to run.

--rawpkt-ops N

stop rawpkt workers after N packets from the sender process are received.

--rawpkt-port N

start at port P. For N rawpkt worker processes, ports P to (P * 4) - 1 are used. The default starting port is port 14000.

--rawpkt-rxring N

setup raw packets with RX ring with N number of blocks, this selects TPACKET_V. N must be one of 1, 2, 4, 8 or 16.

--rawudp N

start N workers that send and receive UDP packets using raw sockets on the localhost. Requires CAP_NET_RAW to run.

--rawudp-if NAME

use network interface NAME. If the interface NAME does not exist, is not up or does not support the domain then the loopback (lo) interface is used as the default.

--rawudp-ops N

stop rawudp workers after N packets are received.

--rawudp-port N

start at port P. For N rawudp worker processes, ports P to (P * 4) - 1 are used. The default starting port is port 13000.

--rdrand N

start N workers that read a random number from an on-chip random number generator This uses the rdrand instruction on Intel x86 processors or the darn instruction on Power9 processors.

--rdrand-ops N

stop rdrand stress workers after N bogo rdrand operations (1 bogo op = 2048 random bits successfully read).

--rdrand-seed

use rdseed instead of rdrand (x86 only).

--readahead N

start N workers that randomly seek and perform 4096 byte read/write I/O operations on a file with readahead. The default file size is 64 MB. Readaheads and reads are batched into 16 readaheads and then 16 reads.

--readahead-bytes N

set the size of readahead file, the default is 1 GB. One can specify the size as % of free space on the file system or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--readahead-ops N

stop readahead stress workers after N bogo read operations.

--reboot N

start N workers that exercise the reboot(2) system call. When possible, it will create a process in a PID namespace and perform a reboot power off command that should shutdown the process. Also, the stressor exercises invalid reboot magic values and invalid reboots when there are insufficient privileges that will not actually reboot the system.

--reboot-ops N

stop the reboot stress workers after N bogo reboot cycles.

--regs N

start N workers that shuffle data around the CPU registers exercising register move instructions. Each bogo-op represents 1000 calls of a shuffling function that shuffles the registers 32 times. Only implemented for the GCC compiler since this requires register annotations and optimization level 0 to compile appropriately.

--regs-ops N

stop regs stressors after N bogo operations.

--remap N

start N workers that map 512 pages and re-order these pages using the deprecated system call remap_file_pages(2). Several page re-orderings are exercised: forward, reverse, random and many pages to 1 page.

--remap-mlock

attempt to mlock mmap'd huge pages into memory causing more memory pressure by preventing pages from swapped out.

--remap-ops N

stop after N remapping bogo operations.

--remap-pages N

specify number of pages to remap, must be a power of 2, default is 512 pages.

-R N, --rename N

start N workers that each create a file and then repeatedly rename it.

--rename-ops N

stop rename stress workers after N bogo rename operations.

--resched N

start N workers that exercise process rescheduling. Each stressor spawns a child process for each of the positive nice levels and iterates over the nice levels from 0 to the lowest priority level (highest nice value). For each of the nice levels 1024 iterations over 3 non-real time scheduling polices SCHED_OTHER, SCHED_BATCH and SCHED_IDLE are set and a sched_yield occurs to force heavy rescheduling activity. When the -v verbose option is used the distribution of the number of yields across the nice levels is printed for the first stressor out of the N stressors.

--resched-ops N

stop after N rescheduling sched_yield calls.

--resources N

start N workers that consume various system resources. Each worker will spawn 1024 child processes that iterate 1024 times consuming shared memory, heap, stack, temporary files and various file descriptors (eventfds, memoryfds, userfaultfds, pipes and sockets).

--resources-mlock

attempt to mlock mmap'd pages into memory causing more memory pressure by preventing pages from swapped out.

--resources-ops N

stop after N resource child forks.

--revio N

start N workers continually writing in reverse position order to temporary files. The default mode is to stress test reverse position ordered writes with randomly sized sparse holes between each write. With the --aggressive option enabled without any --revio-opts options the revio stressor will work through all the --revio-opt options one by one to cover a range of I/O options.

--revio-bytes N

write N bytes for each revio process, the default is 1 GB. One can specify the size as % of free space on the file system or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--revio-opts list

specify various stress test options as a comma separated list. Options are the same as --hdd-opts but without the iovec option.

--revio-ops N

stop revio stress workers after N bogo operations.

--revio-write-size N

specify size of each write in bytes. Size can be from 1 byte to 4 MB.

--ring-pipe N

start N workers that move data around a ring of pipes using poll to detect when data is ready to copy. By default, 256 pipes are used with two 4096 byte items of data being copied around the ring of pipes. Data is copied using read and write system calls. If the splice system call is available then one can use splice to use more efficient in-kernel data passing instead of buffer copying.

--ring-pipe-num N

specify the number of pipes to use. Ranges from 4 to 262144, default is 256.

--ring-pipe-ops N

stop after N pipe data transfers.

--ring-pipe-size N

specify the size of data being copied in bytes. Ranges from 1 to 4096, default is 4096.

--ring-pipe-splice

enable splice to move data between pipes (only if splice() is available).

--rlimit N

start N workers that exceed CPU and file size resource imits, generating SIGXCPU and SIGXFSZ signals.

--rlimit-ops N

stop after N bogo resource limited SIGXCPU and SIGXFSZ signals have been caught.

--rmap N

start N workers that exercise the VM reverse-mapping. This creates 16 processes per worker that write/read multiple file-backed memory mappings. There are 64 lots of 4 page mappings made onto the file, with each mapping overlapping the previous by 3 pages and at least 1 page of non-mapped memory between each of the mappings. Data is synchronously msync'd to the file 1 in every 256 iterations in a random manner.

--rmap-ops N

stop after N bogo rmap memory writes/reads.

--rotate N

start N workers that exercise 1 bit rotates left and right of unsigned integer variables. The default will rotate four 8, 16, 32, 64 (and if supported 128) bit values 10000 times in a loop per bogo-op.

--rotate-method method

specify the method of rotation to use. The 'all' method uses all the methods and is the default.

Method	Description
all	exercise with all the rotate stressor methods (see below):
rol8	8 bit unsigned rotate left by 1 bit
ror8	8 bit unsigned rotate right by 1 bit
rol16	16 bit unsigned rotate left by 1 bit
ror16	16 bit unsigned rotate right by 1 bit
rol32	32 bit unsigned rotate left by 1 bit
ror32	32 bit unsigned rotate right by 1 bit
rol64	64 bit unsigned rotate left by 1 bit
ror64	64 bit unsigned rotate right by 1 bit
rol128	128 bit unsigned rotate left by 1 bit
ror128	128 bit unsigned rotate right by 1 bit

--rotate-ops N

stop after N bogo rotate operations.

--rseq N

start N workers that exercise restartable sequences via the rseq(2) system call. This loops over a long duration critical section that is likely to be interrupted. A rseq abort handler keeps count of the number of interruptions and a SIGSEV handler also tracks any failed rseq aborts that can occur if there is a mismatch in a rseq check signature. Linux only.

--rseq-ops N

stop after N bogo rseq operations. Each bogo rseq operation is equivalent to 10000 iterations over a long duration rseq handled critical section.

--rtc N

start N workers that exercise the real time clock (RTC) interfaces via /dev/rtc and /sys/class/rtc/rtc0. No destructive writes (modifications) are performed on the RTC. This is a Linux only stressor.

--rtc-ops N

stop after N bogo RTC interface accesses.

--schedmix N

start N workers that each start child processes that repeatedly select random a scheduling policy and then executes a short duration randomly chosen time consuming activity. This exercises rapid re-scheduling of processes and generates a large amount of scheduling timer interrupts.

--schedmix-ops N

stop after N scheduling mixed operations.

--schedmix-procs N

specify the number of chid processes to run for each stressor instance, range from 1 to 64, default is 16.

--schedpolicy N

start N workers that set the worker to various available scheduling policies out of SCHED_OTHER, SCHED_BATCH, SCHED_IDLE, SCHED_FIFO, SCHED_RR, SCHED_DEADLINE and SCHED_EXT. For the real time scheduling policies a random sched priority is selected between the minimum and maximum scheduling priority settings.

--schedpolicy-ops N

stop after N bogo scheduling policy changes.

--schedpolicy-rand

Select scheduling policy randomly so that the new policy is always different to the previous policy. The default is to work through the scheduling policies sequentially.

--sctp N

start N workers that perform network sctp stress activity using the Stream Control Transmission Protocol (SCTP). This involves client/server processes performing rapid connect, send/receives and disconnects on the local host.

--sctp-domain D

specify the domain to use, the default is ipv4. Currently ipv4 and ipv6 are supported.

--sctp-if NAME

use network interface NAME. If the interface NAME does not exist, is not up or does not support the domain then the loopback (lo) interface is used as the default.

--sctp-ops N

stop sctp workers after N bogo operations.

--sctp-port P

start at sctp port P. For N sctp worker processes, ports P to (P * 4) - 1 are used for ipv4, ipv6 domains and ports P to P - 1 are used for the unix domain.

--sctp-sched [ fc | fcfs | prio | rr | wfq ]

specify SCTP scheduler, one of fc (fair capacity), fcfs (first come first served, the default), prio (priority), rr (round-robin) or wfq (weighted fair queueing)

--seal N

start N workers that exercise the fcntl(2) SEAL commands on a small anonymous file created using memfd_create(2). After each SEAL command is issued the stressor also sanity checks if the seal operation has sealed the file correctly. (Linux only).

--seal-ops N

stop after N bogo seal operations.

--seccomp N

start N workers that exercise Secure Computing system call filtering. Each worker creates child processes that write a short message to /dev/null and then exits. 2% of the child processes have a seccomp filter that disallows the write system call and hence it is killed by seccomp with a SIGSYS. Note that this stressor can generate many audit log messages each time the child is killed. Requires CAP_SYS_ADMIN to run.

--seccomp-ops N

stop seccomp stress workers after N seccomp filter tests.

--secretmem N

start N workers that mmap pages using file mapping off a memfd_secret file descriptor. Each stress loop iteration will expand the mappable region by 3 pages using ftruncate and mmap and touches the pages. The pages are then fragmented by unmapping the middle page and then umapping the first and last pages. This tries to force page fragmentation and also trigger out of memory (OOM) kills of the stressor when the secret memory is exhausted. Note this is a Linux 5.11+ only stressor and the kernel needs to be booted with "secretmem=" option to allocate a secret memory reservation.

--secretmem-ops N

stop secretmem stress workers after N stress loop iterations.

--seek N

start N workers that randomly seeks and performs 512 byte read/write I/O operations on a file. The default file size is 16 GB.

--seek-ops N

stop seek stress workers after N bogo seek operations.

--seek-punch

punch randomly located 8 K holes into the file to cause more extents to force a more demanding seek stressor, (Linux only).

--seek-size N

specify the size of the file in bytes. Small file sizes allow the I/O to occur in the cache, causing greater CPU load. Large file sizes force more I/O operations to drive causing more wait time and more I/O on the drive. One can specify the size in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--sem N

start N workers that perform POSIX semaphore wait and post operations. By default, a parent and 4 children are started per worker to provide some contention on the semaphore. This stresses fast semaphore operations and produces rapid context switching.

--sem-ops N

stop semaphore stress workers after N bogo semaphore operations.

--sem-procs N

start N child workers per worker to provide contention on the semaphore, the default is 4 and a maximum of 64 are allowed.

--sem-shared

share the semaphore across all sem stressor instances. Normally each semaphore stressor shares a semaphore with its child processes, this option produces more locking contention and less throughput by sharing a semaphore across all semaphore stressor processes.

--sem-sysv N

start N workers that perform System V semaphore wait and post operations. By default, a parent and 4 children are started per worker to provide some contention on the semaphore. This stresses fast semaphore operations and produces rapid context switching.

--sem-sysv-ops N

stop semaphore stress workers after N bogo System V semaphore operations.

--sem-sysv-procs N

start N child processes per worker to provide contention on the System V semaphore, the default is 4 and a maximum of 64 are allowed.

--sem-sysv-setall

sets the semval values for all the semaphores in the child's semaphore set. This depends on the semctl SETALL op being defined and GETALL succeeding and is an opt-in option as it will affect the semaphore being exercised.

--sendfile N

start N workers that send an empty file to /dev/null. This operation spends nearly all the time in the kernel. The default sendfile size is 4 MB. The sendfile options are for Linux only.

--sendfile-ops N

stop sendfile workers after N sendfile bogo operations.

--sendfile-size S

specify the size to be copied with each sendfile call. The default size is 4 MB. One can specify the size in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--session N

start N workers that create child and grandchild processes that set and get their session ids. 25% of the grandchild processes are not waited for by the child to create orphaned sessions that need to be reaped by init.

--session-ops N

stop session workers after N child processes are spawned and reaped.

--set N

start N workers that call system calls that try to set data in the kernel, currently these are: setgid, sethostname, setpgid, setpgrp, setuid, setgroups, setreuid, setregid, setresuid, setresgid and setrlimit. Some of these system calls are OS specific.

--set-ops N

stop set workers after N bogo set operations.

--shellsort N

start N workers that sort 32 bit integers using shellsort.

--shellsort-ops N

stop shellsort stress workers after N bogo shellsorts.

--shellsort-size N

specify number of 32 bit integers to sort, default is 262144 (256 × 1024).

--shm N

start N workers that open and allocate shared memory objects using the POSIX shared memory interfaces. By default, the test will repeatedly create and destroy 32 shared memory objects, each of which is 8 MB in size.

--shm-bytes N

specify the size of the POSIX shared memory objects to be created. One can specify the size as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--shm-mlock

attempt to mlock shared memory objects into memory causing more memory pressure by preventing pages from swapped out.

--shm-objs N

specify the number of shared memory objects to be created.

--shm-ops N

stop after N POSIX shared memory create and destroy bogo operations are complete.

--shm-sysv N

start N workers that allocate shared memory using the System V shared memory interface. By default, the test will repeatedly create and destroy 8 shared memory segments, each of which is 8 MB in size.

--shm-sysv-bytes N

specify the size of the shared memory segment to be created. One can specify the size as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--shm-sysv-mlock

attempt to mlock shared memory segment into memory causing more memory pressure by preventing pages from swapped out.

--shm-sysv-ops N

stop after N shared memory create and destroy bogo operations are complete.

--shm-sysv-segs N

specify the number of shared memory segments to be created. The default is 8 segments.

--sigabrt N

start N workers that create children that are killed by SIGABRT signals or by calling abort(3).

--sigabrt-ops N

stop the sigabrt workers after N SIGABRT signals are successfully handled.

--sigbus N

start N workers that rapidly create and catch bus errors generated via misaligned access and accessing a file backed memory mapping that does not have file storage to back the page being accessed.

--sigbus-ops N

stop sigbus stress workers after N bogo bus errors.

--sigchld N

start N workers that create children to generate SIGCHLD signals. This exercises children that exit (CLD_EXITED), get killed (CLD_KILLED), get stopped (CLD_STOPPED) or continued (CLD_CONTINUED).

--sigchld-ops N

stop the sigchld workers after N SIGCHLD signals are successfully handled.

--sigfd N

start N workers that generate SIGRT signals and are handled by reads by a child process using a file descriptor set up using signalfd(2). (Linux only). This will generate a heavy context switch load when all CPUs are fully loaded.

--sigfd-ops

stop sigfd workers after N bogo SIGUSR1 signals are sent.

--sigfpe N

start N workers that rapidly cause division by zero SIGFPE faults.

--sigfpe-ops N

stop sigfpe stress workers after N bogo SIGFPE faults.

--sighup N

start N workers that generate SIGHUP signals using raise(2) and by killing a group leader process with a child process indirectly receiving SIGHUP when it loses the group leader.

--sighup-ops N

stop sighup stressor workers after N SIGHUP signals

--sigill N

start N workers that execute illegal instructions to generate SIGILL signals.

--sigill-ops N

stop sigill stressor workers after N SIGILL signals

--sigio N

start N workers that read data from a child process via a pipe and generate SIGIO signals. This exercises asynchronous I/O via SIGIO.

--sigio-ops N

stop sigio stress workers after handling N SIGIO signals.

--signal N

start N workers that exercise the signal system call three different signal handlers, SIG_IGN (ignore), a SIGCHLD handler and SIG_DFL (default action). For the SIGCHLD handler, the stressor sends itself a SIGCHLD signal and checks if it has been handled. For other handlers, the stressor checks that the SIGCHLD handler has not been called. This stress test calls the signal system call directly when possible and will try to avoid the C library attempt to replace signal with the more modern sigaction system call.

--signal-ops N

stop signal stress workers after N rounds of signal handler setting.

--signest N

start N workers that exercise nested signal handling. A signal is raised and inside the signal handler a different signal is raised, working through a list of signals to exercise. An alternative signal stack is used that is large enough to handle all the nested signal calls. The -v option will log the approximate size of the stack required and the average stack size per nested call.

--signest-ops N

stop after handling N nested signals.

--sigpending N

start N workers that check if SIGUSR1 signals are pending. This stressor masks SIGUSR1, generates a SIGUSR1 signal and uses sigpending(2) to see if the signal is pending. Then it unmasks the signal and checks if the signal is no longer pending.

--sigpending-ops N

stop sigpending stress workers after N bogo sigpending pending/unpending checks.

--sigpipe N

start N workers that repeatedly spawn off child process that exits before a parent can complete a pipe write, causing a SIGPIPE signal. The child process is either spawned using clone(2) if it is available or use the slower fork(2) instead.

--sigpipe-ops N

stop N workers after N SIGPIPE signals have been caught and handled.

--sigq N

start N workers that rapidly send SIGUSR1 signals using sigqueue(3) to child processes that wait for the signal via sigwaitinfo(2).

--sigq-ops N

stop sigq stress workers after N bogo signal send operations.

--sigrt N

start N workers that each create child processes to handle SIGRTMIN to SIGRMAX real time signals. The parent sends each child process a RT signal via siqueue(2) and the child process waits for this via sigwaitinfo(2). When the child receives the signal it then sends a RT signal to one of the other child processes also via sigqueue(2).

--sigrt-ops N

stop sigrt stress workers after N bogo sigqueue signal send operations.

--sigsegv N

start N workers that rapidly create and catch segmentation faults generated via illegal memory access, illegal vdso system calls, illegal port reads, illegal interrupts or access to x86 time stamp counter.

--sigsegv-ops N

stop sigsegv stress workers after N bogo segmentation faults.

--sigsuspend N

start N workers that each spawn off 4 child processes that wait for a SIGUSR1 signal from the parent using sigsuspend(2). The parent sends SIGUSR1 signals to each child in rapid succession. Each sigsuspend wakeup is counted as one bogo operation.

--sigsuspend-ops N

stop sigsuspend stress workers after N bogo sigsuspend wakeups.

--sigtrap N

start N workers that exercise the SIGTRAP signal. For systems that support SIGTRAP, the signal is generated using raise(SIGTRAP). Only x86 Linux systems the SIGTRAP is also generated by an int 3 instruction.

--sigtrap-ops N

stop sigtrap stress workers after N SIGTRAP signals have been handled.

--sigurg N

start workers that exercise the SIGURG signal by sending out-of-band data over a TCP/IP IPv4 socket stream.

--sigurg-ops N

stop sigurg stressor workers after N SIGURG signals have been handled.

--sigvtalrm N

start N workers that exercise the SIGVTALRM signal using an ITIMER_VIRTUAL itimer and a busy loop that consumes CPU time calling getitimer for the ITIMER_VIRTUAL timer.

--sigvtalrm-ops N

stop sigvtalrm stress workers after N SIGVTALRM signals have been handled.

--sigxcpu N

start N workers that exercise the SIGXCPU stressor. A busy loop generates SIGXCPU signals by setting a 0 second run time limit followed by a sched_yield call.

--sigxcpu-ops N

stop sigsxcpu stress workers after N bogo SIGXCPU signal attempts.

--sigxfsz N

start N workers that exercise the SIGXFSZ stressor. A random 32 bit file size limit is set and data is written outside this size limit to generate a SIGXFSZ signal.

--sigxfsz-ops N

stop sigsxfsz stress workers after N bogo SIGXFSZ signal attempts.

--skiplist N

start N workers that store and then search for integers using a skiplist. By default, 65536 integers are added and searched. This is a useful method to exercise random access of memory and processor cache.

--skiplist-ops N

stop the skiplist worker after N skiplist store and search cycles are completed.

--skiplist-size N

specify the size (number of integers) to store and search in the skiplist. Size can be from 1 K to 4 M.

--sleep N

start N workers that spawn off multiple threads that each perform multiple sleeps of ranges 1us to 0.1s. This creates multiple context switches and timer interrupts.

--sleep-max P

start P threads per worker. The default is 1024, the maximum allowed is 30000.

--sleep-ops N

stop after N sleep bogo operations.

--smi N

start N workers that attempt to generate system management interrupts (SMIs) into the x86 ring -2 system management mode (SMM) by exercising the advanced power management (APM) port 0xb2. This requires the --pathological option and root privilege and is only implemented on x86 Linux platforms. This probably does not work in a virtualized environment. The stressor will attempt to determine the time stolen by SMIs with some naïve benchmarking.

--smi-ops N

stop after N attempts to trigger the SMI.

-S N, --sock N

start N workers that perform various socket stress activity. This involves a pair of client/server processes performing rapid connect, send and receives and disconnects on the local host.

--sock-domain D

specify the domain to use, the default is ipv4. Currently ipv4, ipv6 and unix are supported.

--sock-if NAME

use network interface NAME. If the interface NAME does not exist, is not up or does not support the domain then the loopback (lo) interface is used as the default.

--sock-msgs N

send N messages per connect, send/receive, disconnect iteration. The default is 1000 messages. If N is too small then the rate is throttled back by the overhead of socket connect and disconnect (on Linux, one needs to increase /proc/sys/net/netfilter/nf_conntrack_max to allow more connections).

--sock-nodelay

This disables the TCP Nagle algorithm, so data segments are always sent as soon as possible. This stops data from being buffered before being transmitted, hence resulting in poorer network utilisation and more context switches between the sender and receiver.

--sock-ops N

stop socket stress workers after N bogo operations.

--sock-opts [ random | send | sendmsg | sendmmsg ]

by default, messages are sent using send(2). This option allows one to specify the sending method using send(2), sendmsg(2), sendmmsg(2) or a random selection of one of these 3 on each iteration. Note that sendmmsg is only available for Linux systems that support this system call.

--sock-port P

start at socket port P. For N socket worker processes, ports P to P - 1 are used.

--sock-protocol P

Use the specified protocol P, default is tcp. Options are tcp and mptcp (if supported by the operating system).

--sock-type [ stream | seqpacket ]

specify the socket type to use. The default type is stream. seqpacket currently only works for the unix socket domain.

--sock-zerocopy

enable zerocopy for send and recv calls if the MSG_ZEROCOPY is supported.

--sockabuse N

start N workers that abuse a socket file descriptor with various file based system that don't normally act on sockets. The kernel should handle these illegal and unexpected calls gracefully.

--sockabuse-ops N

stop after N iterations of the socket abusing stressor loop.

--sockabuse-port P

start at socket port P. For N sockabuse worker processes, ports P to P - 1 are used.

--sockdiag N

start N workers that exercise the Linux sock_diag netlink socket diagnostics (Linux only). This currently requests diagnostics using UDIAG_SHOW_NAME, UDIAG_SHOW_VFS, UDIAG_SHOW_PEER, UDIAG_SHOW_ICONS, UDIAG_SHOW_RQLEN and UDIAG_SHOW_MEMINFO for the AF_UNIX family of socket connections.

--sockdiag-ops N

stop after receiving N sock_diag diagnostic messages.

--sockfd N

start N workers that pass file descriptors over a UNIX domain socket using the CMSG(3) ancillary data mechanism. For each worker, pair of client/server processes are created, the server opens as many file descriptors on /dev/null as possible and passing these over the socket to a client that reads these from the CMSG data and immediately closes the files.

--sockfd-ops N

stop sockfd stress workers after N bogo operations.

--sockfd-port P

start at socket port P. For N socket worker processes, ports P to P - 1 are used.

--sockfd-reuse

re-use the file descriptor by passing it back from the receiver to the sender and re-sending it again rather than opening /dev/null each time.

--sockmany N

start N workers that use a client process to attempt to open as many as 100000 TCP/IP socket connections to a server on port 10000.

--sockmany-if NAME

use network interface NAME. If the interface NAME does not exist, is not up or does not support the domain then the loopback (lo) interface is used as the default.

--sockmany-ops N

stop after N connections.

--sockmany-port P

start at socket port P. For N sockmany worker processes, ports P to P - 1 are used.

--sockpair N

start N workers that perform socket pair I/O read/writes. This involves a pair of client/server processes performing randomly sized socket I/O operations.

--sockpair-ops N

stop socket pair stress workers after N bogo operations.

--softlockup N

start N workers that flip between with the "real-time" SCHED_FIO and SCHED_RR scheduling policies at the highest priority to force softlockups. This can only be run with CAP_SYS_NICE capability and for best results the number of stressors should be at least the number of online CPUs. Once running, this is practically impossible to stop and it will force softlockup issues and may trigger watchdog timeout reboots.

--softlockup-ops N

stop softlockup stress workers after N bogo scheduler policy changes.

--sparsematrix N

start N workers that exercise 3 different sparse matrix implementations based on hashing, Judy array (for 64 bit systems), 2-d circular linked-lists, memory mapped 2-d matrix (non-sparse), quick hashing (on preallocated nodes) and red-black tree. The sparse matrix is populated with values, random values potentially non-existing values are read, known existing values are read and known existing values are marked as zero. This default 500 × 500 sparse matrix is used and 5000 items are put into the sparse matrix making it 2% utilized.

--sparsematrix-items N

populate the sparse matrix with N items. If N is greater than the number of elements in the sparse matrix than N will be capped to create at 100% full sparse matrix.

--sparsematrix-method [ all | hash | hashjudy | judy | list | mmap | qhash | rb ]

specify the type of sparse matrix implementation to use. The 'all' method uses all the methods and is the default.

Method	Description
all	exercise with all the sparsematrix stressor methods (see below):
hash	use a hash table and allocate nodes on the heap for each unique value at a (x, y) matrix position.
hashjudy	use a hash table for x coordinates and a Judy array for y coordinates for values at a (x, y) matrix position.
judy	use a Judy array with a unique 1-to-1 mapping of (x, y) matrix position into the array.
list	use a circular linked-list for sparse y positions each with circular linked-lists for sparse x positions for the (x, y) matrix coordinates.
mmap	use a non-sparse mmap the entire 2-d matrix space. Only (x, y) matrix positions that are referenced will get physically mapped. Note that large sparse matrices cannot be mmap'd due to lack of virtual address limitations, and too many referenced pages can trigger the out of memory killer on Linux.
qhash	use a hash table with pre-allocated nodes for each unique value. This is a quick hash table implementation, nodes are not allocated each time with calloc and are allocated from a pre-allocated pool leading to quicker hash table performance than the hash method.
rb	use a red-black balanced tree using one tree node for each unique value at a (x, y) matrix position.
splay	use a splay tree using one tree node for each unique value at a (x, y) matrix position.

--sparsematrix-ops N

stop after N sparsematrix test iterations.

--sparsematrix-size N

use a N × N sized sparse matrix

--spawn N

start N workers continually spawn children using posix_spawn(3) that exec stress-ng and then exit almost immediately. Currently Linux only.

--spawn-ops N

stop spawn stress workers after N bogo spawns.

--spinmem N

start N workers that use a shared memory page to keep two processes synchronized using busy spin loops. One process is a writer that increments a value in memory slot 0 and spin waits for the data to appear in memory slot 1. The other process spin waits for the data to change in slot 0 and copies the changed value into memory slot 1. The stessor benchmarks the time for the transactions to occur between both processes. Note that the optimal number of stressors is half the number of online CPUs in a system. By default 32 bit write/reads are used.

--spinmem-affinity

move spinmem stressor processes to randomly selected CPUs every million spinmem transactions.

--spinmem-ops N

stop after N spinmem bogo operations. A bogo operation is 1000 transactions betewen the two spinmem proceesses.

--spinmem-method [ 8bit | 16bit | 32bit | 64bit ]

select the size of the memory write/reads, the default is 32 bit.

--splice N

move data from /dev/zero to /dev/null through a pipe without any copying between kernel address space and user address space using splice(2). This is only available for Linux.

--splice-bytes N

transfer N bytes per splice call, the default is 64 K. One can specify the size as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--splice-ops N

stop after N bogo splice operations.

--stack N

start N workers that rapidly cause and catch stack overflows by use of large recursive stack allocations. Much like the brk stressor, this can eat up pages rapidly and may trigger the kernel OOM killer on the process, however, the killed stressor is respawned again by a monitoring parent process.

--stack-fill

the default action is to touch the lowest page on each stack allocation. This option touches all the pages by filling the new stack allocation with zeros which forces physical pages to be allocated and hence is more aggressive.

--stack-mlock

attempt to mlock stack pages into memory causing more memory pressure by preventing pages from swapped out.

--stack-ops N

stop stack stress workers after N bogo stack overflows.

--stack-pageout

force stack pages out to swap (available when madvise(2) supports MADV_PAGEOUT).

--stack-unmap

unmap a single page in the middle of a large buffer allocated on the stack on each stack allocation. This forces the stack mapping into multiple separate allocation mappings.

--stackmmap N

start N workers that use a 2 MB stack that is memory mapped onto a temporary file. A recursive function works down the stack and flushes dirty stack pages back to the memory mapped file using msync(2) until the end of the stack is reached (stack overflow). This exercises dirty page and stack exception handling.

--stackmmap-ops N

stop workers after N stack overflows have occurred.