man2/times.2

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   3 .\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
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  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@gmx.net>
  30 .\"     Added note on non-standard behaviour when SIGCHLD is ignored.
  31 .\" Modified 2004-11-16, mtk, Noted that the non-conformance 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 non-standard behaviour: Linux allows 'buf' to
  36 .\"     be NULL, but POSIX.1 doesn't specify this and it's non-portable.
  37 .\"
  38 .TH TIMES 2 2002-06-14 "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 .IR buf
  51 points to.
  52 The
  53 .I struct tms
  54 is as defined in
  55 .IR <sys/times.h> :
  56 .sp
  57 .nf
  58 struct tms {
  59 .RS
  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 .RE
  65 };
  66 .fi
  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 is 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 For Linux 2.4 and earlier this point is the moment the system was booted.
 106 Since Linux 2.6, this point is \fI(2^32/HZ) \- 300\fP
 107 (i.e., about 429 million) seconds before system boot time.
 108 The return value may overflow the possible range of type
 109 .IR clock_t .
 110 On error, \fI(clock_t) \-1\fP is returned, and
 111 .I errno
 112 is set appropriately.
 113 .SH NOTES
 114 The number of clock ticks per second can be obtained using
 115 .RS
 116 sysconf(_SC_CLK_TCK);
 117 .RE
 118 In POSIX-1996 the symbol CLK_TCK (defined in
 119 .IR <time.h> )
 120 is mentioned as obsolescent.
 121 It is obsolete now.
 122 .PP
 123 In Linux kernel versions before 2.6.9,
 124 if the disposition of
 125 .B SIGCHLD
 126 is set to
 127 .B SIG_IGN
 128 then the times of terminated children
 129 are automatically included in the
 130 .I tms_cstime
 131 and
 132 .I tms_cutime
 133 fields, although POSIX.1-2001 says that this should only happen
 134 if the calling process
 135 .BR wait ()s
 136 on its children.
 137 This non-conformance is rectified in Linux 2.6.9 and later.
 138 .\" See the description of times() in XSH, which says:
 139 .\"     The times of a terminated child process are included... when wait()
 140 .\"     or waitpid() returns the process ID of this terminated child.
 141
 142 On Linux, the
 143 .I buf
 144 argument can be specified as NULL, with the result that
 145 .BR times ()
 146 just returns a function result.
 147 However, POSIX does not specify this behaviour, and most
 148 other Unix implementations require a non-NULL value for
 149 .IR buf .
 150 .LP
 151 Note that
 152 .BR clock (3)
 153 returns values of type
 154 .I clock_t
 155 that are not measured in clock ticks
 156 but in
 157 .BR CLOCKS_PER_SEC .
 158 .SH "CONFORMING TO"
 159 SVr4, 4.3BSD, POSIX.1-2001.
 160 .SH "HISTORICAL NOTES"
 161 SVr1-3 returns
 162 .I long
 163 and the struct members are of type
 164 .I time_t
 165 although they store clock ticks, not seconds since the epoch.
 166 V7 used
 167 .I long
 168 for the struct members, because it had no type
 169 .I time_t
 170 yet.
 171 .PP
 172 On older systems the number of clock ticks per second is given
 173 by the variable HZ.
 174 .SH "SEE ALSO"
 175 .BR time (1),
 176 .BR getrusage (2),
 177 .BR wait (2),
 178 .BR clock (3),
 179 .BR sysconf (3),
 180 .BR time (7)