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PROLOG

       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

       times — get process and waited-for child process times

SYNOPSIS

       #include <sys/times.h>

       clock_t times(struct tms *buffer);

DESCRIPTION

       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 used.

       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

       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

       The times() function shall fail if:

       EOVERFLOW
              The return value would overflow the range of clock_t.

       The following sections are informative.

EXAMPLES

   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 times.

           #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;
           ...
           void
           start_clock()
           {
               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. */
           void
           end_clock(char *msg)
           {
               en_time = times(&en_cpu);

               fputs(msg,stdout);
               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));
           }

APPLICATION USAGE

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

RATIONALE

       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().

       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.

FUTURE DIRECTIONS

       None.

SEE ALSO

       alarm(), exec, fork(), sysconf(), time(), wait(), waitid()

       The Base Definitions volume of POSIX.1‐2017, <sys_times.h>

COPYRIGHT

       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 .