man2/times.2

   1 .\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
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  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 2017-09-15 "Linux" "Linux Programmer's Manual"
  39 .SH NAME
  40 times \- get process times
  41 .SH SYNOPSIS
  42 .B #include <sys/times.h>
  43 .PP
  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 .PP
  57 .in +4n
  58 .EX
  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 .EE
  66 .in
  67 .PP
  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 executing inside the kernel
  75 while performing tasks on behalf of the calling process.
  76 .PP
  77 The
  78 .I tms_cutime
  79 field contains the sum of the
  80 .I tms_utime
  81 and
  82 .I tms_cutime
  83 values for all waited-for terminated children.
  84 The
  85 .I tms_cstime
  86 field contains the sum of the
  87 .I tms_stime
  88 and
  89 .I tms_cstime
  90 values for all waited-for terminated children.
  91 .PP
  92 Times for terminated children (and their descendants)
  93 are added in at the moment
  94 .BR wait (2)
  95 or
  96 .BR waitpid (2)
  97 returns their process ID.
  98 In particular, times of grandchildren
  99 that the children did not wait for are never seen.
 100 .PP
 101 All times reported are in clock ticks.
 102 .SH RETURN VALUE
 103 .BR times ()
 104 returns the number of clock ticks that have elapsed since
 105 an arbitrary point in the past.
 106 The return value may overflow the possible range of type
 107 .IR clock_t .
 108 On error, \fI(clock_t)\ \-1\fP is returned, and
 109 .I errno
 110 is set appropriately.
 111 .SH ERRORS
 112 .TP
 113 .B EFAULT
 114 .I tms
 115 points outside the process's address space.
 116 .SH CONFORMING TO
 117 POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
 118 .SH NOTES
 119 The number of clock ticks per second can be obtained using:
 120 .PP
 121 .in +4n
 122 .EX
 123 sysconf(_SC_CLK_TCK);
 124 .EE
 125 .in
 126 .PP
 127 In POSIX.1-1996 the symbol \fBCLK_TCK\fP (defined in
 128 .IR <time.h> )
 129 is mentioned as obsolescent.
 130 It is obsolete now.
 131 .PP
 132 In Linux kernel versions before 2.6.9,
 133 if the disposition of
 134 .B SIGCHLD
 135 is set to
 136 .BR SIG_IGN ,
 137 then the times of terminated children
 138 are automatically included in the
 139 .I tms_cstime
 140 and
 141 .I tms_cutime
 142 fields, although POSIX.1-2001 says that this should happen
 143 only if the calling process
 144 .BR wait (2)s
 145 on its children.
 146 This nonconformance is rectified in Linux 2.6.9 and later.
 147 .\" See the description of times() in XSH, which says:
 148 .\"     The times of a terminated child process are included... when wait()
 149 .\"     or waitpid() returns the process ID of this terminated child.
 150 .PP
 151 On Linux, the
 152 .I buf
 153 argument can be specified as NULL, with the result that
 154 .BR times ()
 155 just returns a function result.
 156 However, POSIX does not specify this behavior, and most
 157 other UNIX implementations require a non-NULL value for
 158 .IR buf .
 159 .PP
 160 Note that
 161 .BR clock (3)
 162 also returns a value of type
 163 .IR clock_t ,
 164 but this value is measured in units of
 165 .BR CLOCKS_PER_SEC ,
 166 not the clock ticks used by
 167 .BR times ().
 168 .PP
 169 On Linux, the "arbitrary point in the past" from which the return value of
 170 .BR times ()
 171 is measured has varied across kernel versions.
 172 On Linux 2.4 and earlier, this point is the moment the system was booted.
 173 Since Linux 2.6, this point is \fI(2^32/HZ) \- 300\fP
 174 seconds before system boot time.
 175 This variability across kernel versions (and across UNIX implementations),
 176 combined with the fact that the returned value may overflow the range of
 177 .IR clock_t ,
 178 means that a portable application would be wise to avoid using this value.
 179 To measure changes in elapsed time, use
 180 .BR clock_gettime (2)
 181 instead.
 182 .\" .PP
 183 .\" On older systems the number of clock ticks per second is given
 184 .\" by the variable HZ.
 185 .SS Historical
 186 SVr1-3 returns
 187 .I long
 188 and the struct members are of type
 189 .I time_t
 190 although they store clock ticks, not seconds since the Epoch.
 191 V7 used
 192 .I long
 193 for the struct members, because it had no type
 194 .I time_t
 195 yet.
 196 .SH BUGS
 197 A limitation of the Linux system call conventions on some architectures
 198 (notably i386) means that on Linux 2.6 there is a small time window
 199 (41 seconds) soon after boot when
 200 .BR times ()
 201 can return \-1, falsely indicating that an error occurred.
 202 The same problem can occur when the return value wraps past
 203 the maximum value that can be stored in
 204 .BR clock_t .
 205 .\" The problem is that a syscall return of -4095 to -1
 206 .\" is interpreted by glibc as an error, and the wrapper converts
 207 .\" the return value to -1.
 208 .\" http://marc.info/?l=linux-kernel&m=119447727031225&w=2
 209 .\" "compat_sys_times() bogus until jiffies >= 0"
 210 .\" November 2007
 211 .SH SEE ALSO
 212 .BR time (1),
 213 .BR getrusage (2),
 214 .BR wait (2),
 215 .BR clock (3),
 216 .BR sysconf (3),
 217 .BR time (7)