time(7) Miscellaneous Information Manual time(7) time - (real time) -- , , ( (Epoch) ), (, ) ( (elapsed time)). (process time) -- , . (user) (system). -- , . -- , , , (, ). time(1) , . times(2), getrusage(2) clock(3). ( ) , . rtc(4) hwclock(8). , HZ (jiffies) , (timeouts) (, select(2), sigtimedwait(2)) (, getrusage(2)), (software clock) -- , , (jiffies). HZ. The value of HZ varies across kernel versions and hardware platforms. On i386 the situation is as follows: on kernels up to and including Linux 2.4.x, HZ was 100, giving a jiffy value of 0.01 seconds; starting with Linux 2.6.0, HZ was raised to 1000, giving a jiffy of 0.001 seconds. Since Linux 2.6.13, the HZ value is a kernel configuration parameter and can be 100, 250 (the default) or 1000, yielding a jiffies value of, respectively, 0.01, 0.004, or 0.001 seconds. Since Linux 2.6.20, a further frequency is available: 300, a number that divides evenly for the common video frame rates (PAL, 25 Hz; NTSC, 30 Hz). times(2) -- . , USER_HZ. sysconf(_SC_CLK_TCK). System and process clocks; time namespaces The kernel supports a range of clocks that measure various kinds of elapsed and virtual (i.e., consumed CPU) time. These clocks are described in clock_gettime(2). A few of the clocks are settable using clock_settime(2). The values of certain clocks are virtualized by time namespaces; see time_namespaces(7). Linux 2.6.21 ( ) . Linux 2.6.21, Linux (HRT), CONFIG_HIGH_RES_TIMERS. , HRT, , ( , , ). , clock_getres(2) <> /proc/timer_list. HRTs are not supported on all hardware architectures. (Support is provided on x86, ARM, and PowerPC, among others.) UNIX (Epoch), 1970-01-01 00:00:00 +0000 (UTC). c CLOCK_REALTIME clock_gettime(2), ( ), ; time(2) , . clock_settime(2). , Certain library functions use a structure of type tm to represent broken-down time, which stores time value separated out into distinct components (year, month, day, hour, minute, second, etc.). This structure is described in tm(3type), which also describes functions that convert between calendar time and broken-down time. Functions for converting between broken-down time and printable string representations of the time are described in ctime(3), strftime(3), and strptime(3). ( ) ; nanosleep(2), clock_nanosleep(2) sleep(3). , - , , , ; alarm(2), getitimer(2), timerfd_create(2) timer_create(2). Linux 2.6.28, << >> (timer slack) . -- , , . , . PR_SET_TIMERSLACK prctl(2). . date(1), time(1), timeout(1), adjtimex(2), alarm(2), clock_gettime(2), clock_nanosleep(2), getitimer(2), getrlimit(2), getrusage(2), gettimeofday(2), nanosleep(2), stat(2), time(2), timer_create(2), timerfd_create(2), times(2), utime(2), adjtime(3), clock(3), clock_getcpuclockid(3), ctime(3), ntp_adjtime(3), ntp_gettime(3), pthread_getcpuclockid(3), sleep(3), strftime(3), strptime(3), timeradd(3), usleep(3), rtc(4), time_namespaces(7), hwclock(8) Azamat Hackimov , Dmitry Bolkhovskikh , Yuri Kozlov ; GNU 3 , . . , , . Linux man-pages 6.06 31 2023 . time(7)