times (2) - Linux Manuals
times: get process times
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 {
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 particular, times of grandchildren
that the children did not wait for are never seen.
All times reported are in clock ticks.
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It is obsolete now.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.
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
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
NOTES
The number of clock ticks per second can be obtained using:
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.
COLOPHON
This page is part of release 5.10 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/.