times(2) — Linux manual page


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 instruc‐
       tions of the calling process.  The tms_stime field contains the CPU
       time spent executing inside the kernel while performing tasks on be‐
       half 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 par‐
       ticular, 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 appropriately.

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:


       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  It is obsolete now.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 automat‐
       ically 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 be‐
       fore system boot time.  This variability across kernel versions (and
       across UNIX implementations), combined with the fact that the re‐
       turned 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.

       SVr1-3 returns long and the struct members are of type time_t al‐
       though 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 5.09 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

Linux                            2017-09-15                         TIMES(2)

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