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.

STANDARDS

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

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       is obsolete now.

       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 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

       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)