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 in the system while executing 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 appropriately.

ERRORS         top

       EFAULT tms points outside the process's address space.

CONFORMING TO         top

       SVr4, 4.3BSD, POSIX.1-2001.

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  It is obsolete now.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 (i.e., about 429
       million) 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 3.75 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
       http://www.kernel.org/doc/man-pages/.

Linux                            2012-10-22                         TIMES(2)