times(3p) — Linux manual page


TIMES(3P)               POSIX Programmer's Manual              TIMES(3P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The
       Linux implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior),
       or the interface may not be implemented on Linux.

NAME         top

       times — get process and waited-for child process times

SYNOPSIS         top

       #include <sys/times.h>

       clock_t times(struct tms *buffer);

DESCRIPTION         top

       The times() function shall fill the tms structure pointed to by
       buffer with time-accounting information. The tms structure is
       defined in <sys/times.h>.

       All times are measured in terms of the number of clock ticks

       The times of a terminated child process shall be included in the
       tms_cutime and tms_cstime elements of the parent when wait(),
       waitid(), or waitpid() returns the process ID of this terminated
       child. If a child process has not waited for its children, their
       times shall not be included in its times.

        *  The tms_utime structure member is the CPU time charged for
           the execution of user instructions of the calling process.

        *  The tms_stime structure member is the CPU time charged for
           execution by the system on behalf of the calling process.

        *  The tms_cutime structure member is the sum of the tms_utime
           and tms_cutime times of the child processes.

        *  The tms_cstime structure member is the sum of the tms_stime
           and tms_cstime times of the child processes.

RETURN VALUE         top

       Upon successful completion, times() shall return the elapsed real
       time, in clock ticks, since an arbitrary point in the past (for
       example, system start-up time). This point does not change from
       one invocation of times() within the process to another. The
       return value may overflow the possible range of type clock_t.  If
       times() fails, (clock_t)-1 shall be returned and errno set to
       indicate the error.

ERRORS         top

       The times() function shall fail if:

              The return value would overflow the range of clock_t.

       The following sections are informative.

EXAMPLES         top

   Timing a Database Lookup
       The following example defines two functions, start_clock() and
       end_clock(), that are used to time a lookup. It also defines
       variables of type clock_t and tms to measure the duration of
       transactions. The start_clock() function saves the beginning
       times given by the times() function. The end_clock() function
       gets the ending times and prints the difference between the two

           #include <sys/times.h>
           #include <stdio.h>
           void start_clock(void);
           void end_clock(char *msg);
           static clock_t st_time;
           static clock_t en_time;
           static struct tms st_cpu;
           static struct tms en_cpu;
               st_time = times(&st_cpu);

           /* This example assumes that the result of each subtraction
              is within the range of values that can be represented in
              an integer type. */
           end_clock(char *msg)
               en_time = times(&en_cpu);

               printf("Real Time: %jd, User Time %jd, System Time %jd\n",
                   (intmax_t)(en_time - st_time),
                   (intmax_t)(en_cpu.tms_utime - st_cpu.tms_utime),
                   (intmax_t)(en_cpu.tms_stime - st_cpu.tms_stime));


       Applications should use sysconf(_SC_CLK_TCK) to determine the
       number of clock ticks per second as it may vary from system to

RATIONALE         top

       The accuracy of the times reported is intentionally left
       unspecified to allow implementations flexibility in design, from
       uniprocessor to multi-processor networks.

       The inclusion of times of child processes is recursive, so that a
       parent process may collect the total times of all of its
       descendants.  But the times of a child are only added to those of
       its parent when its parent successfully waits on the child. Thus,
       it is not guaranteed that a parent process can always see the
       total times of all its descendants; see also the discussion of
       the term ``realtime'' in alarm(3p).

       If the type clock_t is defined to be a signed 32-bit integer, it
       overflows in somewhat more than a year if there are 60 clock
       ticks per second, or less than a year if there are 100. There are
       individual systems that run continuously for longer than that.
       This volume of POSIX.1‐2017 permits an implementation to make the
       reference point for the returned value be the start-up time of
       the process, rather than system start-up time.

       The term ``charge'' in this context has nothing to do with
       billing for services. The operating system accounts for time used
       in this way. That information must be correct, regardless of how
       that information is used.



SEE ALSO         top

       alarm(3p), exec(1p), fork(3p), sysconf(3p), time(3p), wait(3p),

       The Base Definitions volume of POSIX.1‐2017, sys_times.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any
       discrepancy between this version and the original IEEE and The
       Open Group Standard, the original IEEE and The Open Group
       Standard is the referee document. The original Standard can be
       obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page
       are most likely to have been introduced during the conversion of
       the source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group               2017                         TIMES(3P)

Pages that refer to this page: sys_times.h(0p)time(1p)clock(3p)exec(3p)fork(3p)getdate(3p)getrusage(3p)posix_spawn(3p)time(3p)