RNGD(8)                     System Manager's Manual                    RNGD(8)



NAME
       rngd - Check and feed random data from hardware device to kernel random
       device


SYNOPSIS
       rngd [-b, --background] [-f, --foreground] [-d, --debug] [-l, --list]
       [-x, --exclude] [-n, --include] [-O, --option] [-i, --ignorefail] [-o,
       --random-device=file] [-p, --pid-file=file] [-r, --rng-device=file]
       [-s, --random-step=nnn] [-t, --test] [-W, --fill-watermark=nnn] [-R,
       --force-reseed=nnn] [-D, --drop-privileges=user:group] [-q, --quiet]
       [-?, --help] [-v, --version]


DESCRIPTION
       This daemon feeds data from a random number generator to the kernel's
       random number entropy pool, after first checking the data to ensure
       that it is properly random.

       The -f or --foreground options can be used to tell rngd to avoid
       forking on startup.  This is typically used for debugging.  The -b or
       --background options, which fork and put rngd into the background
       automatically, are the default.

       The -r or --rng-device options can be used to select an alternate
       source of input, besides the default /dev/hwrng.  The -o or --random-
       device options can be used to select an alternate entropy output
       device, besides the default /dev/random.  Note that this device must
       support the Linux kernel /dev/random ioctl API.

OPTIONS
       -b, --background
              Become a daemon (default)

       -f, --foreground
              Do not fork and become a daemon

       -d, --debug
              Enable debug messages

       -l, --list
              List the indexes and names of available entropy sources. Exit
              code when listing sources is 0 if at least 1 entropy source was
              found and initialized, 1 otherwise.

       -x, --exclude
              Disable entropy sources based on index or (shortname) reported
              from --list option

       -n, --include
              Enable entropy sources based on index or (shortname) reported
              from --list option

       -O, --option
              Provide specific config options to individual entropy sources,
              in the format --option [index|shortname]:key:value.  See Entropy
              Sources section below for indices and source specific options.
              Note that specifying -O [<index>|<shortname>] will print the
              available options for that index to the console.

       -p file, --pid-file=file
              File used for recording daemon PID, and multiple exclusion
              (default: /var/run/rngd.pid)

       -i, --ignorefail
              Ignore repeated fips failures

       -o file, --random-device=file
              Kernel device used for random number output (default:
              /dev/random)

       -r file, --rng-device=file
              Kernel device used for random number input (default: /dev/hwrng)

       -s nnn, --random-step=nnn
              Number of bytes written to random-device at a time (default: 64)

       -t, --test
              Enter test mode.  In this mode (which implies -f), all generated
              entropy is discarded and rngd reports the amount of entropy
              generated every second.

       -e nnn, --entropy-count=nnn
              Number of bits to consider random when adding entropy. 1<=e<=8
              (default: 8)

       -W n, --fill-watermark=nnn
              Once we start doing it, feed entropy to random-device until at
              least fill-watermark bits of entropy are available in its
              entropy pool.  By default, this value is set to 75% of the
              entropy pool size or 2048 bits if the entropy pool size couldn't
              be determined.  Setting this too high will cause rngd to
              dominate the contents of the entropy pool.  Low values will hurt
              system performance during entropy starves.  Do not set fill-
              watermark above the size of the entropy pool (usually 4096
              bits).  A value of 0 to this option will cause no watermark to
              be set.

       -R n, --force-reseed=nnn
              For newer kernels which support non-blocking entropy pools, it
              is still beneficial to periodically add fresh entropy as a
              reseeding event.  --force-reseed defines the number of seconds
              between which fresh entropy is added to the kernel entropy pool.
              Defaults to 5 minutes.

       -D, --drop-privileges=user:group
              Drop privileges to a user and a group specified after
              initialization. A user and a group can be specified as a name or
              as a numerical id and must be separated with a colon. A user and
              a group must exist. A default is not to drop privileges.

       -q, --quiet
              Suppress all messages

       -?, --help
              Give a short summary of all program options

       -v, --version
              Print program version


ENTROPY SOURCES
        Rngd is made up of multiple entropy sources, the data from which is
       aggregated and fed into the kernels entropy pool.  Note that not all
       entropy sources are available on all systems, and if an entropy source
       is enabled for a system on which it is not appropriate (or possible) to
       use, it may fail initialization.  It is not fatal to rngd for any
       single entropy source to fail during startup.  Only a single entropy
       sources is needed for rngd to operate.  The following entropy sources
       are currently defined in rngd


       Hardware RNG (hwrng)
              The Hardware RNG is a generic entropy source that draws entropy
              from a hardware rng attached by default to /dev/hwrng


       TPM (tpm)
              Entropy drawn from on board TPM device.  Note this entropy
              source is deprecated and will be removed soon, as newer tpm
              devices export entropy via /dev/hwrng, which is collected by the
              hwrng source above


       RDRAND/RDSEED (rdrand)
              Entropy drawn from the RDRAND and RDSEED instructions (x86 only)

       Options

              use_aes -  select if rdrand is used to seed a cprng to produce
              entropy, or if all entropy is drawn directly from rdrand
              instruction (default 0)


       DARN (darn)
              Entropy drawn from the DARN instruction (ppc64 only)

       Options

              use_aes -  select if the power darn instruction is used to
              directly fill the entropy poll, or if it is used as a periodic
              seed to an aes based cprng (default 1)


       RNDR (rndr)
              Entropy drawn from the RNDR instruction (aarch64 only)


       Options

              use_aes -  select if the arm rndr instruction is used to
              directly fill the entropy poll, or if it is used as a periodic
              seed to an aes based cprng (default 0)


       NIST Entropy Beacon (nist)
              Entropy gathered from the NIST network entropy beacon.  Note
              that this entropy source is disabled by default as it should
              never be used for cryptographic purposes, or any use case in
              which random data should be known only by a single entity.


       Qrypt Entropy Beacon (qrypt)
              Entropy gathered from the qrypt entropy beacon.  Note this
              beacon provides entropy to remote clients over a TLS connection.
              As such this source should not be used for cryptographic
              operations unless the security of the network can be guaranteed
              against man in the middle and other network based attacks.


       Options
              tokenfile -  Specify the file containing the access token to the
              Qrypt beacon

              delay -  Specify the maximum delay (in seconds) that the source
              will wait when there are temporary conditions preventing entropy
              retrieval before trying to fetch entropy again. The default
              maximum delay is eight hours, exponentially counting up from one
              second upwards, in powers of two.


       JITTER (jitter)
              Entropy gathered by measuring timing variance of operations on
              the local cpu

       Options
              thread_count -  Set the number of threads that the jitter
              entropy source will spawn

              buffer_size -  Set the size of the buffer cache that each thread
              maintains

              refill_thresh -  Set the low watermark for the cache that
              triggers its corresponding thread to start refill operations

              retry_count -  If all entropy buffers are empty, retry this many
              times before giving up.  Note that jitterentropy can take
              several seconds to refill a buffer, and so retries after a delay
              may be preferable to repeatedly spining on an empty buffer
              (default 1)

              retry_delay -  between each retry for retry_count above, sleep
              for this many seconds. May also be the special value -1,
              representing adaptive sleep, where each retry delay will be half
              the recorded execution time of the last entropy gathering round
              (default -1)

              force_soft_timer -  on platforms with a hardware timer that is
              too coarse to sample jitter, we can instead use a software based
              timer loop.  Detection and use of this mechanism is automatic,
              but this can be useful for testing purposes


       PKCS11 (pkcs11)
              Entropy gathered via the opensc openssl engine, which can
              extract entropy from various smart card readers

       Options
              engine_path -  Set the patch for the pkcs11 engine DSO to load

              chunk_size -  Some pkcs11 engines have restrictions on how much
              data can be requested at a time, this option allows for the
              request to be subdivided into smaller chunks to be satisfied


       RTLSDR (rtlsdr)
              Entropy gathered via the rtl software defined radio library,
              which can gather entropy using various usb software defined
              radios listening to random radio static

       Options
              devid -  When multiple devices are available the integer index
              of the device to use

              freq_min -  The minimum frequence range to scan in

              freq_max -  The maximum frequency range to scan in

              sample_min -  The minimum sample rate of the radio

              sample_max -  The maximum sample rate of the radio


AUTHORS
       Philipp Rumpf
       Jeff Garzik - jgarzik@pobox.com
       Matt Sottek
       Brad Hill
       Neil Horman - nhorman@tuxdriver.com

rng-tools 6.16                    March 2001                           RNGD(8)