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 executing inside the kernel while performing tasks on behalf of
27 the calling process.
28 The tms_cutime field contains the sum of the tms_utime and tms_cutime
30 values for all waited-for terminated children. The tms_cstime field
31 contains the sum of the tms_stime and tms_cstime values for all waited-
32 for terminated children.
33 Times for terminated children (and their descendants) are added in at
35 the moment wait(2) or waitpid(2) returns their process ID. In particu‐
36 lar, times of grandchildren that the children did not wait for are
37 never seen.
38 All times reported are in clock ticks.
40
42 times() returns the number of clock ticks that have elapsed since an
43 arbitrary point in the past. The return value may overflow the possi‐
44 ble range of type clock_t. On error, (clock_t) -1 is returned, and er‐
45 rno is set to indicate the error.
46
48 EFAULT tms points outside the process's address space.
49
51 POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
52
54 The number of clock ticks per second can be obtained using:
55 sysconf(_SC_CLK_TCK);
57 In POSIX.1-1996 the symbol CLK_TCK (defined in <time.h>) is mentioned
59 as obsolescent. It is obsolete now.
60 In Linux kernel versions before 2.6.9, if the disposition of SIGCHLD is
62 set to SIG_IGN, then the times of terminated children are automatically
63 included in the tms_cstime and tms_cutime fields, although POSIX.1-2001
64 says that this should happen only if the calling process wait(2)s on
65 its children. This nonconformance is rectified in Linux 2.6.9 and
66 later.
67 On Linux, the buf argument can be specified as NULL, with the result
69 that times() just returns a function result. However, POSIX does not
70 specify this behavior, and most other UNIX implementations require a
71 non-NULL value for buf.
72 Note that clock(3) also returns a value of type clock_t, but this value
74 is measured in units of CLOCKS_PER_SEC, not the clock ticks used by
75 times().
76 On Linux, the "arbitrary point in the past" from which the return value
78 of times() is measured has varied across kernel versions. On Linux 2.4
79 and earlier, this point is the moment the system was booted. Since
80 Linux 2.6, this point is (2^32/HZ) - 300 seconds before system boot
81 time. This variability across kernel versions (and across UNIX imple‐
82 mentations), combined with the fact that the returned value may over‐
83 flow the range of clock_t, means that a portable application would be
84 wise to avoid using this value. To measure changes in elapsed time,
85 use clock_gettime(2) instead.
86 Historical
88 SVr1-3 returns long and the struct members are of type time_t although
89 they store clock ticks, not seconds since the Epoch. V7 used long for
90 the struct members, because it had no type time_t yet.
91
93 A limitation of the Linux system call conventions on some architectures
94 (notably i386) means that on Linux 2.6 there is a small time window (41
95 seconds) soon after boot when times() can return -1, falsely indicating
96 that an error occurred. The same problem can occur when the return
97 value wraps past the maximum value that can be stored in clock_t.
98
100 time(1), getrusage(2), wait(2), clock(3), sysconf(3), time(7)
101
103 This page is part of release 5.13 of the Linux man-pages project. A
104 description of the project, information about reporting bugs, and the
105 latest version of this page, can be found at
106 https://www.kernel.org/doc/man-pages/.
107Linux 2021-03-22 TIMES(2)