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[linuxjm/LDP_man-pages.git] / draft / man7 / time.7

.\" Copyright (c) 2006 by Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" 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.\" manual page may be incorrect or out-of-date.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.
.\"
.\" 2008-06-24, mtk: added some details about where jiffies come into
.\"     play; added section on high-resolution timers.
.\"
.\" Japanese Version Copyright (c) 2006 Yuichi SATO
.\"         all rights reserved.
.\" Translated 2006-07-23 by Yuichi SATO <ysato444@yahoo.co.jp>, LDP v2.36
.\" Updated 2007-05-04, Akihiro MOTOKI <amotoki@dd.iij4u.or.jp>, LDP v2.44
.\" Updated 2008-08-10, Akihiro MOTOKI <amotoki@dd.iij4u.or.jp>, LDP v3.05
.\"
.TH TIME 7 2010-02-25 "Linux" "Linux Programmer's Manual"
.\"O .SH NAME
.SH ̾Á°
.\"O time \- overview of time and timers
time \- »þ´Ö¤È¥¿¥¤¥Þ¤Î³µÍ×
.\"O .SH DESCRIPTION
.SH ÀâÌÀ
.\"O .SS "Real time and process time"
.SS "¼Â»þ´Ö (real time) ¤È¥×¥í¥»¥¹»þ´Ö"
.\"O .I "Real time"
.\"O is defined as time measured from some fixed point,
.\"O either from a standard point in the past
.\"O (see the description of the Epoch and calendar time below),
.\"O or from some point (e.g., the start) in the life of a process
.\"O .RI ( "elapsed time" ).
\fI¼Â»þ´Ö\fR¤Ï¡¢ÆÃÄê¤Î»þÅÀ¤«¤é·×¤Ã¤¿»þ´Ö¤ÈÄêµÁ¤µ¤ì¤ë¡£
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(²¼µ­¤Îµª¸µ (Epoch) ¤È¥«¥ì¥ó¥À»þ¹ï¤ÎÀâÌÀ¤ò»²¾È) ¤ä¡¢
¥×¥í¥»¥¹¤Î°ìÀ¸¤Ë¤ª¤±¤ë²¿¤é¤«¤Î»þÅÀ (Î㤨¤Ð¡¢³«»Ï»þ) ¤Ç¤¢¤ë
.RI ( "·Ð²á»þ´Ö" )¡£

.\"O .I "Process time"
.\"O is defined as the amount of CPU time used by a process.
.\"O This is sometimes divided into
.\"O .I user
.\"O and
.\"O .I system
.\"O components.
\fI¥×¥í¥»¥¹»þ´Ö\fR¤Ï¡¢¥×¥í¥»¥¹¤Ë¤è¤Ã¤Æ»È¤ï¤ì¤¿Áí CPU »þ´Ö¤ÈÄêµÁ¤µ¤ì¤ë¡£
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.\"O User CPU time is the time spent executing code in user mode.
.\"O System CPU time is the time spent by the kernel executing
.\"O in system mode on behalf of the process (e.g., executing system calls).
¥æ¡¼¥¶ CPU »þ´Ö¤Ï¡¢¥³¡¼¥É¤ò¥æ¡¼¥¶¥â¡¼¥É¤Ç¼Â¹Ô¤¹¤ë¤Î¤Ë»È¤Ã¤¿»þ´Ö¤Ç¤¢¤ë¡£
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(Î㤨¤Ð¡¢¥·¥¹¥Æ¥à¥³¡¼¥ë¤ò¼Â¹Ô¤¹¤ë¤Î¤Ë»È¤Ã¤¿»þ´Ö)¡£
.\"O The
.\"O .BR time (1)
.\"O command can be used to determine the amount of CPU time consumed
.\"O during the execution of a program.
.BR time (1)
¥³¥Þ¥ó¥É¤Ï¥×¥í¥°¥é¥à¤Î¼Â¹Ô¤ËÈñ¤µ¤ì¤¿Áí CPU »þ´Ö¤ò·×¤ë¤Î¤Ë»ÈÍѤµ¤ì¤ë¡£
.\"O A program can determine the amount of CPU time it has consumed using
.\"O .BR times (2),
.\"O .BR getrusage (2),
.\"O or
.\"O .BR clock (3).
¥×¥í¥°¥é¥à¤Ï¡¢¼«¿È¤¬Èñ¤·¤¿Áí CPU »þ´Ö¤ò
.BR times (2),
.BR getrusage (2),
.BR clock (3)
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.\"O .SS "The Hardware Clock"
.SS ¥Ï¡¼¥É¥¦¥§¥¢¥¯¥í¥Ã¥¯
.\"O Most computers have a (battery-powered) hardware clock which the kernel
.\"O reads at boot time in order to initialize the software clock.
¿¤¯¤Î¥³¥ó¥Ô¥å¡¼¥¿¤¬ (ÅÅÃӤǶîÆ°¤µ¤ì¤ë) ¥Ï¡¼¥É¥¦¥§¥¢¥¯¥í¥Ã¥¯¤ò»ý¤Ã¤Æ¤¤¤ë¡£
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¥Ï¡¼¥É¥¦¥§¥¢¥¯¥í¥Ã¥¯¤òÆɤ߹þ¤à¡£
.\"O For further details, see
.\"O .BR rtc (4)
.\"O and
.\"O .BR hwclock (8).
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.BR rtc (4)
¤È
.BR hwclock (8)
¤ò»²¾È¤¹¤ë¤³¤È¡£
.\"O .SS "The Software Clock, HZ, and Jiffies"
.\"Osato: °Ê²¼¤Ç¤Ï jiffies ¤Ïñ¿ô·Á jiffy ¤ËÅý°ì¤·¤Æ¤¤¤ë¡£
.SS "¥½¥Õ¥È¥¦¥§¥¢¥¯¥í¥Ã¥¯, HZ, Jiffy"
.\"O The accuracy of various system calls that set timeouts,
.\"O (e.g.,
.\"O .BR select (2),
.\"O .BR sigtimedwait (2))
.\"O .\" semtimedop(), mq_timedwait(), io_getevents(), poll() are the same
.\"O .\" futexes and thus sem_timedwait() seem to use high-res timers.
.\"O and measure CPU time (e.g.,
.\"O .BR getrusage (2))
.\"O is limited by the resolution of the
.\"O .IR "software clock" ,
.\"O a clock maintained by the kernel which measures time in
.\"O .IR jiffies .
.\"O The size of a jiffy is determined by the value of the kernel constant
.\"O .IR HZ .
¥¿¥¤¥à¥¢¥¦¥È¤òÀßÄꤷ¤¿¤ê (Î㤨¤Ð
.BR select (2),
.BR sigtimedwait (2))¡¢
.\" semtimedop(), mq_timedwait(), io_getevents(), poll() ¤ÏƱ¤¸ futex ¤Ç¤¢¤ê¡¢
.\" ¤·¤¿¤¬¤Ã¤Ã¤Æ sem_timedwait() ¤Ï¹âÀºÅÙ¥¿¥¤¥Þ¤ò»ÈÍѤ·¤Æ¤¤¤ë¤è¤¦¤Ç¤¢¤ë¡£
CPU »þ´Ö¤ò·×¬¤·¤¿¤ê (Î㤨¤Ð
.BR getrusage (2)) ¤¹¤ëÍÍ¡¹¤Ê¥·¥¹¥Æ¥à¥³¡¼¥ë¤ÎÀºÅÙ¤Ï
.I ¥½¥Õ¥È¥¦¥§¥¢¥¯¥í¥Ã¥¯
¤Îʬ²òǽ (resolution) ¤ËÀ©¸Â¤µ¤ì¤ë¡£
¥½¥Õ¥È¥¦¥§¥¢¥¯¥í¥Ã¥¯¤È¤Ï¡¢¥«¡¼¥Í¥ë¤¬´ÉÍý¤¹¤ë
.I jiffy
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jiffy ¤ÎÂ礭¤µ¤Ï¥«¡¼¥Í¥ëÄê¿ô
.I HZ
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.\"O The value of
.\"O .I HZ
.\"O varies across kernel versions and hardware platforms.
.I HZ
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.\"O On i386 the situation is as follows:
.\"O on kernels up to and including 2.4.x, HZ was 100,
.\"O giving a jiffy value of 0.01 seconds;
.\"O starting with 2.6.0, HZ was raised to 1000, giving a jiffy of
.\"O 0.001 seconds.
.\"O Since kernel 2.6.13, the HZ value is a kernel
.\"O configuration parameter and can be 100, 250 (the default) or 1000,
.\"O yielding a jiffies value of, respectively, 0.01, 0.004, or 0.001 seconds.
i386 ¤Î¾ì¹ç¤Ï°Ê²¼¤ÎÄ̤ê¤Ç¤¢¤ë:
2.4.x ¤È¤½¤ì¤è¤êÁ°¤Î¥«¡¼¥Í¥ë¤Ç¤Ï¡¢HZ ¤Ï 100 ¤Ç¤¢¤Ã¤¿¤Î¤Ç¡¢
jiffy ¤ÎÃÍ¤Ï 0.01 ÉäˤʤäƤ¤¤¿¡£
2.6.0 °Ê¹ß¤Ç¤Ï¡¢HZ ¤Ï 1000 ¤ËÁý¤ä¤µ¤ì¤¿¤Î¤Ç¡¢jiffy ¤ÎÃÍ¤Ï 0.001 ÉäǤ¢¤ë¡£
¥«¡¼¥Í¥ë 2.6.13 °Ê¹ß¤Ç¤Ï¡¢HZ ¤ÎÃͤϥ«¡¼¥Í¥ëÀßÄê¥Ñ¥é¥á¡¼¥¿¤Ë¤Ê¤ê¡¢
100, 250 (¥Ç¥Õ¥©¥ë¥È), 1000 ¤È¤¤¤¦ÃͤˤǤ­¤ë¡£
¤½¤ì¤¾¤ì jiffy ¤ÎÃÍ¤Ï 0.01, 0.004, 0.001 Éäˤʤ롣
.\"O Since kernel 2.6.20, a further frequency is available:
.\"O 300, a number that divides evenly for the common video
.\"O frame rates (PAL, 25 HZ; NTSC, 30 HZ).
¥«¡¼¥Í¥ë 2.6.20 °Ê¹ß¤Ç¤Ï¡¢300 ¤âÍøÍѤǤ­¤ë¤è¤¦¤Ë¤Ê¤Ã¤Æ¤¤¤ë¡£
300 ¤Ï°ìÈÌŪ¤Ê±ÇÁü¥Õ¥ì¡¼¥à¥ì¡¼¥È¤Î¸øÇÜ¿ô¤Ç¤¢¤ë (PAL, 25HZ; NTSC, 30HZ)¡£

.\"O The
.\"O .BR times (2)
.\"O system call is a special case.
.\"O It reports times with a granularity defined by the kernel constant
.\"O .IR USER_HZ .
.\"O Userspace applications can determine the value of this constant using
.\"O .IR sysconf(_SC_CLK_TCK) .
.BR times (2)
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¤³¤Î¥·¥¹¥Æ¥à¥³¡¼¥ë¤Ï¥«¡¼¥Í¥ëÄê¿ô
.I USER_HZ
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¥æ¡¼¥¶¶õ´Ö¤Î¥¢¥×¥ê¥±¡¼¥·¥ç¥ó¤Ï
.I sysconf(_SC_CLK_TCK)
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.\" glibc gets this info with a little help from the ELF loader;
.\" see glibc elf/dl-support.c and kernel fs/binfmt_elf.c.
.\"
.\"O .SS "High-Resolution Timers"
.SS "¹âÀºÅÙ¥¿¥¤¥Þ"
.\"O Before Linux 2.6.21, the accuracy of timer and sleep system calls
.\"O (see below) was also limited by the size of the jiffy.
Linux 2.6.21 ¤è¤êÁ°¤Ç¤Ï¡¢¥¿¥¤¥Þ¤ä¥¹¥ê¡¼¥×´ØÏ¢¤Î¥·¥¹¥Æ¥à¥³¡¼¥ë¤ÎÀºÅÙ¤â
jiffy ¤Î¥µ¥¤¥º¤Ë¤è¤êÀ©¸Â¤µ¤ì¤Æ¤¤¤¿¡£

.\"O Since Linux 2.6.21, Linux supports high-resolution timers (HRTs),
.\"O optionally configurable via
.\"O .BR CONFIG_HIGH_RES_TIMERS .
.\"O On a system that supports HRTs, the accuracy of sleep and timer
.\"O system calls is no longer constrained by the jiffy,
.\"O but instead can be as accurate as the hardware allows
.\"O (microsecond accuracy is typical of modern hardware).
.\"O You can determine whether high-resolution timers are supported by
.\"O checking the resolution returned by a call to
.\"O .BR clock_getres (2)
.\"O or looking at the "resolution" entries in
.\"O .IR /proc/timer_list .
Linux 2.6.21 °Ê¹ß¤Ç¤Ï¡¢Linux ¤Ï¹âÀºÅÙ¥¿¥¤¥Þ (high-resolution timers; HRTs)
¤ò¥µ¥Ý¡¼¥È¤·¤Æ¤ª¤ê¡¢
.B CONFIG_HIGH_RES_TIMERS
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¤ÎÀºÅ٤Ϥâ¤Ï¤ä jiffy ¤ËÀ©Ì󤵤ì¤ë¤³¤È¤Ï¤Ê¤¯¡¢
¥Ï¡¼¥É¥¦¥§¥¢¤¬µö¤¹¸Â¤ê¤ÎÀºÅ٤Ȥʤë
(ºÇ¶á¤Î¥Ï¡¼¥É¥¦¥§¥¢¤Ç¤Ï¥Þ¥¤¥¯¥íÉÃñ°Ì¤ÎÀºÅÙ¤¬°ìÈÌŪ¤Ç¤¢¤ë)¡£
¹âÀºÅÙ¥¿¥¤¥Þ¤¬¥µ¥Ý¡¼¥È¤µ¤ì¤Æ¤¤¤ë¤«¤Ï¡¢
.BR clock_getres (2)
¤ò¸Æ¤Ó½Ð¤·¤Æʬ²òǽ¤ò³Îǧ¤¹¤ë¤«¡¢
.I /proc/timer_list
Æâ¤Î "resolution" ¥¨¥ó¥È¥ê¤ò»²¾È¤¹¤ë¤«¤ÇȽÃǤǤ­¤ë¡£

.\"O HRTs are not supported on all hardware architectures.
.\"O (Support is provided on x86, arm, and powerpc, among others.)
¹âÀºÅÙ¥¿¥¤¥Þ¤Ï¤¹¤Ù¤Æ¤Î¥Ï¡¼¥É¥¦¥§¥¢¥¢¡¼¥­¥Æ¥¯¥Á¥ã¤Ç¥µ¥Ý¡¼¥È¤µ¤ì¤Æ¤¤¤ë
Ìõ¤Ç¤Ï¤Ê¤¤ (Âбþ¤·¤Æ¤¤¤ë¥¢¡¼¥­¥Æ¥¯¥Á¥ã¤Ï x86, arm, powerpc ¤Ç¤¢¤ë)¡£
.\"O .SS "The Epoch"
.SS "µª¸µ"
.\"O Unix systems represent time in seconds since the
.\"O .IR Epoch ,
.\"O 1970-01-01 00:00:00 +0000 (UTC).
Unix ¥·¥¹¥Æ¥à¤Ï»þ¹ï¤ò
µª¸µ (1970-01-01 00:00:00 +0000 (UTC)) ¤«¤é¤ÎÉÿô¤Çɽ¸½¤¹¤ë¡£

.\"O A program can determine the
.\"O .I "calendar time"
.\"O using
.\"O .BR gettimeofday (2),
.\"O which returns time (in seconds and microseconds) that have
.\"O elapsed since the Epoch;
¥×¥í¥°¥é¥à¤Ï \fI¥«¥ì¥ó¥À»þ¹ï\fR ¤ò
.BR gettimeofday (2)
¤ò»È¤Ã¤Æ·×¤ë¤³¤È¤¬¤Ç¤­¤ë¡£
¤³¤Î´Ø¿ô¤Ïµª¸µ¤«¤é¤Î·Ð²á»þ´Ö¤ò (Éäȥޥ¤¥¯¥íÉäÇ) ÊÖ¤¹¡£
.\"O .BR time (2)
.\"O provides similar information, but only with accuracy to the
.\"O nearest second.
.\"O The system time can be changed using
.\"O .BR settimeofday (2).
.BR time (2)
¤ÏƱÍͤξðÊó¤òÄ󶡤¹¤ë¤¬¡¢ºÇ¤â¶á¤¤ÉäÎÀºÅÙ¤·¤«¤Ê¤¤¡£
¥·¥¹¥Æ¥à»þ¹ï¤Ï
.BR settimeofday (2)
¤ÇÊѹ¹¤Ç¤­¤ë¡£
.\"O .SS "Broken-down time"
.SS "Í×ÁÇÊ̤λþ¹ï"
.\"O Certain library functions use a structure of
.\"O type
.\"O .I tm
.\"O to represent
.\"O .IR "broken-down time" ,
.\"O which stores time value separated out into distinct components
.\"O (year, month, day, hour, minute, second, etc.).
¥é¥¤¥Ö¥é¥ê´Ø¿ô¤ÎÃæ¤Ë¤Ï
.I tm
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¤³¤Î¹½Â¤ÂΤÏ\fIÍ×ÁÇÊ̤λþ¹ï\fR¤òɽ¤·¡¢
»þ¹ï¤ÎÃͤòÊÌ¡¹¤ÎÍ×ÁÇ (ǯ¡¦·î¡¦Æü¡¦»þ¡¦Ê¬¡¦ÉäʤÉ) ¤Ëʬ¤±¤Æ³ÊǼ¤¹¤ë¡£
.\"O This structure is described in
.\"O .BR ctime (3),
.\"O which also describes functions that convert between calendar time and
.\"O broken-down time.
¤³¤Î¹½Â¤ÂΤÏ
.BR ctime (3)
¤Ëµ­½Ò¤µ¤ì¤Æ¤ª¤ê¡¢¥«¥ì¥ó¥À»þ¹ï¤òÍ×ÁÇÊ̤λþ¹ï¤ËÊÑ´¹¤¹¤ë
´Ø¿ô¤Ë¤Ä¤¤¤Æ¤âµ­½Ò¤µ¤ì¤Æ¤¤¤ë¡£
.\"O Functions for converting between broken-down time and printable
.\"O string representations of the time are described in
.\"O .BR ctime (3),
.\"O .BR strftime (3),
.\"O and
.\"O .BR strptime (3).
Í×ÁÇÊ̤λþ¹ï¤òɽ¼¨²Äǽ¤Êʸ»úÎó¤ËÊÑ´¹¤¹¤ë´Ø¿ô¤Ë¤Ä¤¤¤Æ¤Ï¡¢
.BR ctime (3),
.BR strftime (3),
.BR strptime (3)
¤Ëµ­½Ò¤µ¤ì¤Æ¤¤¤ë¡£
.\"O .SS "Sleeping and Setting Timers"
.SS "¥¿¥¤¥Þ¤Î¥¹¥ê¡¼¥×¤ÈÀßÄê"
.\"O Various system calls and functions allow a program to sleep
.\"O (suspend execution) for a specified period of time; see
.\"O .BR nanosleep (2),
.\"O .BR clock_nanosleep (2),
.\"O and
.\"O .BR sleep (3).
ÍÍ¡¹¤Ê¥·¥¹¥Æ¥à¥³¡¼¥ë¤È´Ø¿ô¤Ë¤è¤ê¡¢»ØÄꤵ¤ì¤¿°ìÄê¤Î»þ´Ö¡¢
¥×¥í¥°¥é¥à¤Ï¥¹¥ê¡¼¥× (¼Â¹Ô¤òÄä»ß) ¤¹¤ë¤³¤È¤¬²Äǽ¤Ç¤¢¤ë¡£
.BR nanosleep (2),
.BR clock_nanosleep (2),
.BR sleep (3)
¤ò»²¾È¤¹¤ë¤³¤È¡£

.\"O Various system calls allow a process to set a timer that expires
.\"O at some point in the future, and optionally at repeated intervals;
.\"O see
.\"O .BR alarm (2),
.\"O .BR getitimer (2),
.\"O .BR timerfd_create (2),
.\"O and
.\"O .BR timer_create (2).
ÍÍ¡¹¤Ê¥·¥¹¥Æ¥à¥³¡¼¥ë¤Ë¤è¤ê¡¢¥×¥í¥»¥¹¤Ï¾­Íè¤Î¤¢¤ë»þÅÀ¤Ç
Í­¸ú´ü´Ö¤¬½ªÎ»¤¹¤ë¥¿¥¤¥Þ¤òÀßÄê¤Ç¤­¤ë¡£
¤Þ¤¿¥ª¥×¥·¥ç¥ó¤È¤·¤Æ·«¤êÊÖ¤·´Ö³Ö¤¬»ØÄê¤Ç¤­¤ë¤â¤Î¤â¤¢¤ë¡£
.BR alarm (2),
.BR getitimer (2),
.BR timerfd_create (2),
.BR timer_create (2)
¤ò»²¾È¤¹¤ë¤³¤È¡£
.\"O .SH "SEE ALSO"
.SH ´ØÏ¢¹àÌÜ
.BR date (1),
.BR time (1),
.BR adjtimex (2),
.BR alarm (2),
.BR clock_gettime (2),
.BR clock_nanosleep (2),
.BR getitimer (2),
.BR getrlimit (2),
.BR getrusage (2),
.BR gettimeofday (2),
.BR nanosleep (2),
.BR stat (2),
.BR time (2),
.BR timer_create (2),
.BR timerfd_create (2),
.BR times (2),
.BR utime (2),
.BR adjtime (3),
.BR clock (3),
.BR clock_getcpuclockid (3),
.BR ctime (3),
.BR pthread_getcpuclockid (3),
.BR sleep (3),
.BR strftime (3),
.BR strptime (3),
.BR timeradd (3),
.BR usleep (3),
.BR rtc (4),
.BR hwclock (8)