TIMES(2)                  (2017-09-15)                   TIMES(2)

     NAME
          times - get process times

     SYNOPSIS
          #include <sys/times.h>

          clock_t times(struct tms *buf);

     DESCRIPTION
          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
          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
          EFAULT
               tms points outside the process's address space.

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

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     NOTES
          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  It is obsolete now.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 imple-
          mentations), 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
          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

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

     COLOPHON
          This page is part of release 5.10 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/.

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