1TIMES(2) Linux Programmer's Manual TIMES(2)
2
6 times - get process times
7
9 #include <sys/times.h>
10 clock_t times(struct tms *buf);
12
14 times() stores the current process times in the struct tms that buf
15 points to. The struct tms is as defined in <sys/times.h>:
16 struct tms {
18 clock_t tms_utime; /* user time */
19 clock_t tms_stime; /* system time */
20 clock_t tms_cutime; /* user time of children */
21 clock_t tms_cstime; /* system time of children */
22 };
23 The tms_utime field contains the CPU time spent executing instructions
25 of the calling process. The tms_stime field contains the CPU time
26 spent in the system while executing tasks on behalf of the calling
27 process. The tms_cutime field contains the sum of the tms_utime and
28 tms_cutime values for all waited-for terminated children. The
29 tms_cstime field contains the sum of the tms_stime and tms_cstime val‐
30 ues for all waited-for terminated children.
31 Times for terminated children (and their descendants) are added in at
33 the moment wait(2) or waitpid(2) returns their process ID. In particu‐
34 lar, times of grandchildren that the children did not wait for are
35 never seen.
36 All times reported are in clock ticks.
38
40 times() returns the number of clock ticks that have elapsed since an
41 arbitrary point in the past. The return value may overflow the possi‐
42 ble range of type clock_t. On error, (clock_t) -1 is returned, and
43 errno is set appropriately.
44
46 SVr4, 4.3BSD, POSIX.1-2001.
47
49 The number of clock ticks per second can be obtained using:
50 sysconf(_SC_CLK_TCK);
52 In POSIX.1-1996 the symbol CLK_TCK (defined in <time.h>) is mentioned
54 as obsolescent. It is obsolete now.
55 In Linux kernel versions before 2.6.9, if the disposition of SIGCHLD is
57 set to SIG_IGN then the times of terminated children are automatically
58 included in the tms_cstime and tms_cutime fields, although POSIX.1-2001
59 says that this should only happen if the calling process wait(2)s on
60 its children. This nonconformance is rectified in Linux 2.6.9 and
61 later.
62 On Linux, the buf argument can be specified as NULL, with the result
64 that times() just returns a function result. However, POSIX does not
65 specify this behavior, and most other Unix implementations require a
66 non-NULL value for buf.
67 Note that clock(3) also returns a value of type clock_t, but this value
69 is measured in units of CLOCKS_PER_SEC, not the clock ticks used by
70 times().
71 On Linux, the "arbitrary point in the past" from which the return value
73 of times() is measured has varied across kernel versions. On Linux 2.4
74 and earlier this point is the moment the system was booted. Since
75 Linux 2.6, this point is (2^32/HZ) - 300 (i.e., about 429 million) sec‐
76 onds before system boot time. This variability across kernel versions
77 (and across Unix implementations), combined with the fact that the
78 returned value may overflow the range of clock_t, means that a portable
79 application would be wise to avoid using this value. To measure
80 changes in elapsed time, use gettimeofday(2) instead.
81 Historical
83 SVr1-3 returns long and the struct members are of type time_t although
84 they store clock ticks, not seconds since the Epoch. V7 used long for
85 the struct members, because it had no type time_t yet.
86
88 A limitation of the Linux system call conventions on some architectures
89 (notably i386) means that on Linux 2.6 there is a small time window (41
90 seconds) soon after boot when times() can return -1, falsely indicating
91 that an error occurred. The same problem can occur when the return
92 value wraps passed the maximum value that can be stored in clockid_t.
93
95 time(1), getrusage(2), wait(2), clock(3), sysconf(3), time(7)
96
98 This page is part of release 3.25 of the Linux man-pages project. A
99 description of the project, and information about reporting bugs, can
100 be found at http://www.kernel.org/doc/man-pages/.
101Linux 2008-06-25 TIMES(2)