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man:times

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 executing inside the kernel while performing 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 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.

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  possi-
     ble  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

     POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.

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  It is obsolete now.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 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  seconds  before  system  boot
     time.   This variability across kernel versions (and across UNIX imple-
     mentations), combined with the fact that the returned value  may  over-
     flow  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 past 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 4.16 of the Linux man-pages project.  A
     description of the project, information about reporting bugs,  and  the
     latest     version     of     this    page,    can    be    found    at
     https://www.kernel.org/doc/man-pages/.

Linux 2017-09-15 TIMES(2)

/data/webs/external/dokuwiki/data/pages/man/times.txt · Last modified: 2019/05/17 09:32 by 127.0.0.1

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