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 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

   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.

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  It is obsolete now.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
   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)

COLOPHON

   This  page  is  part of release 4.09 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
   https://www.kernel.org/doc/man-pages/.

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