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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 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 termi‐
nated 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.
ERRORS
EFAULT tms points outside the process's address space.
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is obsolete now.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 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 mea‐
sured 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 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 3.74 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 http://www.kernel.org/doc/man-pages/.
Linux 2012-10-22 TIMES(2)
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