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 EFAULT tms points outside the process's address space.
47
49 SVr4, 4.3BSD, POSIX.1-2001.
50
52 The number of clock ticks per second can be obtained using:
53 sysconf(_SC_CLK_TCK);
55 In POSIX.1-1996 the symbol CLK_TCK (defined in <time.h>) is mentioned
57 as obsolescent. It is obsolete now.
58 In Linux kernel versions before 2.6.9, if the disposition of SIGCHLD is
60 set to SIG_IGN then the times of terminated children are automatically
61 included in the tms_cstime and tms_cutime fields, although POSIX.1-2001
62 says that this should happen only if the calling process wait(2)s on
63 its children. This nonconformance is rectified in Linux 2.6.9 and
64 later.
65 On Linux, the buf argument can be specified as NULL, with the result
67 that times() just returns a function result. However, POSIX does not
68 specify this behavior, and most other UNIX implementations require a
69 non-NULL value for buf.
70 Note that clock(3) also returns a value of type clock_t, but this value
72 is measured in units of CLOCKS_PER_SEC, not the clock ticks used by
73 times().
74 On Linux, the "arbitrary point in the past" from which the return value
76 of times() is measured has varied across kernel versions. On Linux 2.4
77 and earlier this point is the moment the system was booted. Since
78 Linux 2.6, this point is (2^32/HZ) - 300 (i.e., about 429 million) sec‐
79 onds before system boot time. This variability across kernel versions
80 (and across UNIX implementations), combined with the fact that the
81 returned value may overflow the range of clock_t, means that a portable
82 application would be wise to avoid using this value. To measure
83 changes in elapsed time, use clock_gettime(2) instead.
84 Historical
86 SVr1-3 returns long and the struct members are of type time_t although
87 they store clock ticks, not seconds since the Epoch. V7 used long for
88 the struct members, because it had no type time_t yet.
89
91 A limitation of the Linux system call conventions on some architectures
92 (notably i386) means that on Linux 2.6 there is a small time window (41
93 seconds) soon after boot when times() can return -1, falsely indicating
94 that an error occurred. The same problem can occur when the return
95 value wraps passed the maximum value that can be stored in clock_t.
96
98 time(1), getrusage(2), wait(2), clock(3), sysconf(3), time(7)
99
101 This page is part of release 3.53 of the Linux man-pages project. A
102 description of the project, and information about reporting bugs, can
103 be found at http://www.kernel.org/doc/man-pages/.
104Linux 2012-10-22 TIMES(2)