NAME

       times - get process times

LIBRARY

       Standard C library (libc, -lc)

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 to indicate the error.

ERRORS

       EFAULT tms points outside the process's address space.

VERSIONS

       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.

STANDARDS

       POSIX.1-2008.

HISTORY

       POSIX.1-2001, SVr4, 4.3BSD.

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   It  is  obsolete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

       Before  Linux  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 “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.

       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.

NOTES

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

           sysconf(_SC_CLK_TCK);

       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().

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

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