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  con-
       tains the CPU time spent in the system while executing tasks on behalf of the calling process.  The tms_cutime field con-
       tains the sum of the tms_utime and tms_cutime values for all waited-for terminated children.  The tms_cstime  field  con-
       tains 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.

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  It is obsolete now.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 chil-
       dren are automatically included in the tms_cstime and tms_cutime fields, although POSIX.1-2001 says that this should only
       happen 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.  How-
       ever, 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 (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 gettimeof-
       day(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 clockid_t.

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

COLOPHON
       This  page  is  part of release 3.25 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                                                      2008-06-25                                                   TIMES(2)