[thirdparty/man-pages.git] / man2 / times.2

.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
.\"
.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\" %%%LICENSE_END
.\"
.\" Modified by Michael Haardt (michael@moria.de)
.\" Modified Sat Jul 24 14:29:17 1993 by Rik Faith (faith@cs.unc.edu)
.\" Modified 961203 and 001211 and 010326 by aeb@cwi.nl
.\" Modified 001213 by Michael Haardt (michael@moria.de)
.\" Modified 13 Jun 02, Michael Kerrisk <mtk.manpages@gmail.com>
.\"	Added note on nonstandard behavior when SIGCHLD is ignored.
.\" Modified 2004-11-16, mtk, Noted that the nonconformance when
.\"	SIGCHLD is being ignored is fixed in 2.6.9; other minor changes
.\" Modified 2004-12-08, mtk, in 2.6 times() return value changed
.\" 2005-04-13, mtk
.\"	Added notes on nonstandard behavior: Linux allows 'buf' to
.\"	be NULL, but POSIX.1 doesn't specify this and it's nonportable.
.\"
.TH TIMES 2 2012-10-22 "Linux" "Linux Programmer's Manual"
.SH NAME
times \- get process times
.SH SYNOPSIS
.B #include <sys/times.h>
.sp
.BI "clock_t times(struct tms *" buf );
.SH DESCRIPTION
.BR times ()
stores the current process times in the
.I "struct tms"
that
.I buf
points to.
The
.I struct tms
is as defined in
.IR <sys/times.h> :
.sp
.in +4n
.nf
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 */
};
.fi
.in
.LP
The
.I tms_utime
field contains the CPU time spent executing instructions
of the calling process.
The
.I tms_stime
field contains the CPU time spent in the system while
executing tasks on behalf of the calling process.
The
.I tms_cutime
field contains the sum of the
.I tms_utime
and
.I tms_cutime
values for all waited-for terminated children.
The
.I tms_cstime
field contains the sum of the
.I tms_stime
and
.I tms_cstime
values for all waited-for terminated children.
.LP
Times for terminated children (and their descendants)
are added in at the moment
.BR wait (2)
or
.BR waitpid (2)
returns their process ID.
In particular, times of grandchildren
that the children did not wait for are never seen.
.LP
All times reported are in clock ticks.
.SH RETURN VALUE
.BR 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
.IR clock_t .
On error, \fI(clock_t)\ \-1\fP is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EFAULT
.I tms
points outside the process's address space.
.SH CONFORMING TO
SVr4, 4.3BSD, POSIX.1-2001.
.SH NOTES
The number of clock ticks per second can be obtained using:
.in +4n

sysconf(_SC_CLK_TCK);
.in
.PP
In POSIX.1-1996 the symbol \fBCLK_TCK\fP (defined in
.IR <time.h> )
is mentioned as obsolescent.
It is obsolete now.
.PP
In Linux kernel versions before 2.6.9,
if the disposition of
.B SIGCHLD
is set to
.B SIG_IGN
then the times of terminated children
are automatically included in the
.I tms_cstime
and
.I tms_cutime
fields, although POSIX.1-2001 says that this should only happen
if the calling process
.BR wait (2)s
on its children.
This nonconformance is rectified in Linux 2.6.9 and later.
.\" See the description of times() in XSH, which says:
.\"	The times of a terminated child process are included... when wait()
.\"	or waitpid() returns the process ID of this terminated child.

On Linux, the
.I buf
argument can be specified as NULL, with the result that
.BR times ()
just returns a function result.
However, POSIX does not specify this behavior, and most
other UNIX implementations require a non-NULL value for
.IR buf .
.LP
Note that
.BR clock (3)
also returns a value of type
.IR clock_t ,
but this value is measured in units of
.BR CLOCKS_PER_SEC ,
not the clock ticks used by
.BR times ().

On Linux, the "arbitrary point in the past" from which the return value of
.BR 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 \fI(2^32/HZ) \- 300\fP
(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
.IR clock_t ,
means that a portable application would be wise to avoid using this value.
To measure changes in elapsed time, use
.BR clock_gettime (2)
instead.
.\" .PP
.\" On older systems the number of clock ticks per second is given
.\" by the variable HZ.
.SS Historical
SVr1-3 returns
.I long
and the struct members are of type
.I time_t
although they store clock ticks, not seconds since the Epoch.
V7 used
.I long
for the struct members, because it had no type
.I time_t
yet.
.SH 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
.BR times ()
can return \-1, falsely indicating that an error occurred.
The same problem can occur when the return value wraps passed
the maximum value that can be stored in
.BR clock_t .
.\" The problem is that a syscall return of -4095 to -1
.\" is interpreted by glibc as an error, and the wrapper converts
.\" the return value to -1.
.\" http://marc.info/?l=linux-kernel&m=119447727031225&w=2
.\" "compat_sys_times() bogus until jiffies >= 0"
.\" November 2007
.SH SEE ALSO
.BR time (1),
.BR getrusage (2),
.BR wait (2),
.BR clock (3),
.BR sysconf (3),
.BR time (7)
Commit	Line	Data
	1	.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
	2	.\"
	3	.\" %%%LICENSE_START(VERBATIM)
	4	.\" Permission is granted to make and distribute verbatim copies of this
	5	.\" manual provided the copyright notice and this permission notice are
	6	.\" preserved on all copies.
	7	.\"
	8	.\" Permission is granted to copy and distribute modified versions of this
	9	.\" manual under the conditions for verbatim copying, provided that the
	10	.\" entire resulting derived work is distributed under the terms of a
	11	.\" permission notice identical to this one.
	12	.\"
	13	.\" Since the Linux kernel and libraries are constantly changing, this
	14	.\" manual page may be incorrect or out-of-date. The author(s) assume no
	15	.\" responsibility for errors or omissions, or for damages resulting from
	16	.\" the use of the information contained herein. The author(s) may not
	17	.\" have taken the same level of care in the production of this manual,
	18	.\" which is licensed free of charge, as they might when working
	19	.\" professionally.
	20	.\"
	21	.\" Formatted or processed versions of this manual, if unaccompanied by
	22	.\" the source, must acknowledge the copyright and authors of this work.
	23	.\" %%%LICENSE_END
	24	.\"
	25	.\" Modified by Michael Haardt (michael@moria.de)
	26	.\" Modified Sat Jul 24 14:29:17 1993 by Rik Faith (faith@cs.unc.edu)
	27	.\" Modified 961203 and 001211 and 010326 by aeb@cwi.nl
	28	.\" Modified 001213 by Michael Haardt (michael@moria.de)
	29	.\" Modified 13 Jun 02, Michael Kerrisk <mtk.manpages@gmail.com>
	30	.\" Added note on nonstandard behavior when SIGCHLD is ignored.
	31	.\" Modified 2004-11-16, mtk, Noted that the nonconformance when
	32	.\" SIGCHLD is being ignored is fixed in 2.6.9; other minor changes
	33	.\" Modified 2004-12-08, mtk, in 2.6 times() return value changed
	34	.\" 2005-04-13, mtk
	35	.\" Added notes on nonstandard behavior: Linux allows 'buf' to
	36	.\" be NULL, but POSIX.1 doesn't specify this and it's nonportable.
	37	.\"
	38	.TH TIMES 2 2012-10-22 "Linux" "Linux Programmer's Manual"
	39	.SH NAME
	40	times \- get process times
	41	.SH SYNOPSIS
	42	.B #include <sys/times.h>
	43	.sp
	44	.BI "clock_t times(struct tms *" buf );
	45	.SH DESCRIPTION
	46	.BR times ()
	47	stores the current process times in the
	48	.I "struct tms"
	49	that
	50	.I buf
	51	points to.
	52	The
	53	.I struct tms
	54	is as defined in
	55	.IR <sys/times.h> :
	56	.sp
	57	.in +4n
	58	.nf
	59	struct tms {
	60	clock_t tms_utime; /* user time */
	61	clock_t tms_stime; /* system time */
	62	clock_t tms_cutime; /* user time of children */
	63	clock_t tms_cstime; /* system time of children */
	64	};
	65	.fi
	66	.in
	67	.LP
	68	The
	69	.I tms_utime
	70	field contains the CPU time spent executing instructions
	71	of the calling process.
	72	The
	73	.I tms_stime
	74	field contains the CPU time spent in the system while
	75	executing tasks on behalf of the calling process.
	76	The
	77	.I tms_cutime
	78	field contains the sum of the
	79	.I tms_utime
	80	and
	81	.I tms_cutime
	82	values for all waited-for terminated children.
	83	The
	84	.I tms_cstime
	85	field contains the sum of the
	86	.I tms_stime
	87	and
	88	.I tms_cstime
	89	values for all waited-for terminated children.
	90	.LP
	91	Times for terminated children (and their descendants)
	92	are added in at the moment
	93	.BR wait (2)
	94	or
	95	.BR waitpid (2)
	96	returns their process ID.
	97	In particular, times of grandchildren
	98	that the children did not wait for are never seen.
	99	.LP
	100	All times reported are in clock ticks.
	101	.SH RETURN VALUE
	102	.BR times ()
	103	returns the number of clock ticks that have elapsed since
	104	an arbitrary point in the past.
	105	The return value may overflow the possible range of type
	106	.IR clock_t .
	107	On error, \fI(clock_t)\ \-1\fP is returned, and
	108	.I errno
	109	is set appropriately.
	110	.SH ERRORS
	111	.TP
	112	.B EFAULT
	113	.I tms
	114	points outside the process's address space.
	115	.SH CONFORMING TO
	116	SVr4, 4.3BSD, POSIX.1-2001.
	117	.SH NOTES
	118	The number of clock ticks per second can be obtained using:
	119	.in +4n
	120
	121	sysconf(_SC_CLK_TCK);
	122	.in
	123	.PP
	124	In POSIX.1-1996 the symbol \fBCLK_TCK\fP (defined in
	125	.IR <time.h> )
	126	is mentioned as obsolescent.
	127	It is obsolete now.
	128	.PP
	129	In Linux kernel versions before 2.6.9,
	130	if the disposition of
	131	.B SIGCHLD
	132	is set to
	133	.B SIG_IGN
	134	then the times of terminated children
	135	are automatically included in the
	136	.I tms_cstime
	137	and
	138	.I tms_cutime
	139	fields, although POSIX.1-2001 says that this should only happen
	140	if the calling process
	141	.BR wait (2)s
	142	on its children.
	143	This nonconformance is rectified in Linux 2.6.9 and later.
	144	.\" See the description of times() in XSH, which says:
	145	.\" The times of a terminated child process are included... when wait()
	146	.\" or waitpid() returns the process ID of this terminated child.
	147
	148	On Linux, the
	149	.I buf
	150	argument can be specified as NULL, with the result that
	151	.BR times ()
	152	just returns a function result.
	153	However, POSIX does not specify this behavior, and most
	154	other UNIX implementations require a non-NULL value for
	155	.IR buf .
	156	.LP
	157	Note that
	158	.BR clock (3)
	159	also returns a value of type
	160	.IR clock_t ,
	161	but this value is measured in units of
	162	.BR CLOCKS_PER_SEC ,
	163	not the clock ticks used by
	164	.BR times ().
	165
	166	On Linux, the "arbitrary point in the past" from which the return value of
	167	.BR times ()
	168	is measured has varied across kernel versions.
	169	On Linux 2.4 and earlier this point is the moment the system was booted.
	170	Since Linux 2.6, this point is \fI(2^32/HZ) \- 300\fP
	171	(i.e., about 429 million) seconds before system boot time.
	172	This variability across kernel versions (and across UNIX implementations),
	173	combined with the fact that the returned value may overflow the range of
	174	.IR clock_t ,
	175	means that a portable application would be wise to avoid using this value.
	176	To measure changes in elapsed time, use
	177	.BR clock_gettime (2)
	178	instead.
	179	.\" .PP
	180	.\" On older systems the number of clock ticks per second is given
	181	.\" by the variable HZ.
	182	.SS Historical
	183	SVr1-3 returns
	184	.I long
	185	and the struct members are of type
	186	.I time_t
	187	although they store clock ticks, not seconds since the Epoch.
	188	V7 used
	189	.I long
	190	for the struct members, because it had no type
	191	.I time_t
	192	yet.
	193	.SH BUGS
	194	A limitation of the Linux system call conventions on some architectures
	195	(notably i386) means that on Linux 2.6 there is a small time window
	196	(41 seconds) soon after boot when
	197	.BR times ()
	198	can return \-1, falsely indicating that an error occurred.
	199	The same problem can occur when the return value wraps passed
	200	the maximum value that can be stored in
	201	.BR clock_t .
	202	.\" The problem is that a syscall return of -4095 to -1
	203	.\" is interpreted by glibc as an error, and the wrapper converts
	204	.\" the return value to -1.
	205	.\" http://marc.info/?l=linux-kernel&m=119447727031225&w=2
	206	.\" "compat_sys_times() bogus until jiffies >= 0"
	207	.\" November 2007
	208	.SH SEE ALSO
	209	.BR time (1),
	210	.BR getrusage (2),
	211	.BR wait (2),
	212	.BR clock (3),
	213	.BR sysconf (3),
	214	.BR time (7)