times(2) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON

TIMES(2)                Linux Programmer's Manual               TIMES(2)

NAME         top

       times - get process times

SYNOPSIS         top

       #include <sys/times.h>

       clock_t times(struct tms *buf);

DESCRIPTION         top

       times() stores the current process times in the struct tms that
       buf points to.  The struct tms is as defined in <sys/times.h>:

           struct tms {
               clock_t tms_utime;  /* user time */
               clock_t tms_stime;  /* system time */
               clock_t tms_cutime; /* user time of children */
               clock_t tms_cstime; /* system time of children */
           };

       The tms_utime field contains the CPU time spent executing
       instructions of the calling process.  The tms_stime field
       contains the CPU time spent executing inside the kernel while
       performing tasks on behalf of the calling process.

       The tms_cutime field contains the sum of the tms_utime and
       tms_cutime values for all waited-for terminated children.  The
       tms_cstime field contains the sum of the tms_stime and tms_cstime
       values for all waited-for terminated children.

       Times for terminated children (and their descendants) are added
       in at the moment wait(2) or waitpid(2) returns their process ID.
       In particular, times of grandchildren that the children did not
       wait for are never seen.

       All times reported are in clock ticks.

RETURN VALUE         top

       times() returns the number of clock ticks that have elapsed since
       an arbitrary point in the past.  The return value may overflow
       the possible range of type clock_t.  On error, (clock_t) -1 is
       returned, and errno is set to indicate the error.

ERRORS         top

       EFAULT tms points outside the process's address space.

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.

NOTES         top

       The number of clock ticks per second can be obtained using:

           sysconf(_SC_CLK_TCK);

       In POSIX.1-1996 the symbol CLK_TCK (defined in <time.h>) is
       mentioned as obsolescent.  It is obsolete now.

       In Linux kernel versions before 2.6.9, if the disposition of
       SIGCHLD is set to SIG_IGN, then the times of terminated children
       are automatically included in the tms_cstime and tms_cutime
       fields, although POSIX.1-2001 says that this should happen only
       if the calling process wait(2)s on its children.  This
       nonconformance is rectified in Linux 2.6.9 and later.

       On Linux, the buf argument can be specified as NULL, with the
       result that times() just returns a function result.  However,
       POSIX does not specify this behavior, and most other UNIX
       implementations require a non-NULL value for buf.

       Note that clock(3) also returns a value of type clock_t, but this
       value is measured in units of CLOCKS_PER_SEC, not the clock ticks
       used by times().

       On Linux, the "arbitrary point in the past" from which the return
       value of times() is measured has varied across kernel versions.
       On Linux 2.4 and earlier, this point is the moment the system was
       booted.  Since Linux 2.6, this point is (2^32/HZ) - 300 seconds
       before system boot time.  This variability across kernel versions
       (and across UNIX implementations), combined with the fact that
       the returned value may overflow the range of clock_t, means that
       a portable application would be wise to avoid using this value.
       To measure changes in elapsed time, use clock_gettime(2) instead.

   Historical
       SVr1-3 returns long and the struct members are of type time_t
       although they store clock ticks, not seconds since the Epoch.  V7
       used long for the struct members, because it had no type time_t
       yet.

BUGS         top

       A limitation of the Linux system call conventions on some
       architectures (notably i386) means that on Linux 2.6 there is a
       small time window (41 seconds) soon after boot when times() can
       return -1, falsely indicating that an error occurred.  The same
       problem can occur when the return value wraps past the maximum
       value that can be stored in clock_t.

SEE ALSO         top

       time(1), getrusage(2), wait(2), clock(3), sysconf(3), time(7)

COLOPHON         top

       This page is part of release 5.12 of the Linux man-pages project.
       A description of the project, information about reporting bugs,
       and the latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.

Linux                          2021-03-22                       TIMES(2)

Pages that refer to this page: time(1)fork(2)getrusage(2)sigaction(2)syscalls(2)clock(3)getauxval(3)proc(5)pthreads(7)signal-safety(7)system_data_types(7)time(7)