times man page on Archlinux

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TIMES(2)		   Linux Programmer's Manual		      TIMES(2)

       times - get process times

       #include <sys/times.h>

       clock_t times(struct tms *buf);

       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 val‐
       ues 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 particu‐
       lar, times of grandchildren that the children  did  not	wait  for  are
       never seen.

       All times reported are in clock ticks.

       times()	returns	 the  number of clock ticks that have elapsed since an
       arbitrary point in the past.  The return value may overflow the	possi‐
       ble  range  of  type  clock_t.  On error, (clock_t) -1 is returned, and
       errno is set appropriately.

       EFAULT tms points outside the process's address space.

       SVr4, 4.3BSD, POSIX.1-2001.

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


       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	It is obsolete now.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

       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

       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) sec‐
       onds  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.

       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 passed the maximum value that can be stored in clock_t.

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

       This  page  is  part of release 3.65 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

Linux				  2012-10-22			      TIMES(2)

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