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CentOS 7.0 - man page for times (centos section 2)

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TIMES(2)			    Linux Programmer's Manual				 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  termi-
       nated 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
       SVr4, 4.3BSD, POSIX.1-2001.

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       is obsolete now.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 mea-
       sured 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) 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 passed 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 3.53 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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