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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON |
TIMES(2) Linux Programmer's Manual TIMES(2)
times - get process times
#include <sys/times.h>
clock_t times(struct tms *buf);
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 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.
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.
EFAULT tms points outside the process's address space.
POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
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 It is obsolete now.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 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.
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.
time(1), getrusage(2), wait(2), clock(3), sysconf(3), time(7)
This page is part of release 4.12 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 2016-03-15 TIMES(2)
Pages that refer to this page: time(1), fork(2), getrusage(2), sigaction(2), syscalls(2), clock(3), getauxval(3), proc(5), pthreads(7), signal-safety(7), time(7)