1times(2) System Calls Manual times(2)
2
6 times - get process times
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9 Standard C library (libc, -lc)
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12 #include <sys/times.h>
13 clock_t times(struct tms *buf);
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17 times() stores the current process times in the struct tms that buf
18 points to. The struct tms is as defined in <sys/times.h>:
19 struct tms {
21 clock_t tms_utime; /* user time */
22 clock_t tms_stime; /* system time */
23 clock_t tms_cutime; /* user time of children */
24 clock_t tms_cstime; /* system time of children */
25 };
26 The tms_utime field contains the CPU time spent executing instructions
28 of the calling process. The tms_stime field contains the CPU time
29 spent executing inside the kernel while performing tasks on behalf of
30 the calling process.
31 The tms_cutime field contains the sum of the tms_utime and tms_cutime
33 values for all waited-for terminated children. The tms_cstime field
34 contains the sum of the tms_stime and tms_cstime values for all waited-
35 for terminated children.
36 Times for terminated children (and their descendants) are added in at
38 the moment wait(2) or waitpid(2) returns their process ID. In particu‐
39 lar, times of grandchildren that the children did not wait for are
40 never seen.
41 All times reported are in clock ticks.
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45 times() returns the number of clock ticks that have elapsed since an
46 arbitrary point in the past. The return value may overflow the possi‐
47 ble range of type clock_t. On error, (clock_t) -1 is returned, and er‐
48 rno is set to indicate the error.
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51 EFAULT tms points outside the process's address space.
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54 On Linux, the buf argument can be specified as NULL, with the result
55 that times() just returns a function result. However, POSIX does not
56 specify this behavior, and most other UNIX implementations require a
57 non-NULL value for buf.
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60 POSIX.1-2008.
61
63 POSIX.1-2001, SVr4, 4.3BSD.
64 In POSIX.1-1996 the symbol CLK_TCK (defined in <time.h>) is mentioned
66 as obsolescent. It is obsolete now.
67 Before Linux 2.6.9, if the disposition of SIGCHLD is set to SIG_IGN,
69 then the times of terminated children are automatically included in the
70 tms_cstime and tms_cutime fields, although POSIX.1-2001 says that this
71 should happen only if the calling process wait(2)s on its children.
72 This nonconformance is rectified in Linux 2.6.9 and later.
73 On Linux, the “arbitrary point in the past” from which the return value
75 of times() is measured has varied across kernel versions. On Linux 2.4
76 and earlier, this point is the moment the system was booted. Since
77 Linux 2.6, this point is (2^32/HZ) - 300 seconds before system boot
78 time. This variability across kernel versions (and across UNIX imple‐
79 mentations), combined with the fact that the returned value may over‐
80 flow the range of clock_t, means that a portable application would be
81 wise to avoid using this value. To measure changes in elapsed time,
82 use clock_gettime(2) instead.
83 SVr1-3 returns long and the struct members are of type time_t although
85 they store clock ticks, not seconds since the Epoch. V7 used long for
86 the struct members, because it had no type time_t yet.
87
89 The number of clock ticks per second can be obtained using:
90 sysconf(_SC_CLK_TCK);
92 Note that clock(3) also returns a value of type clock_t, but this value
94 is measured in units of CLOCKS_PER_SEC, not the clock ticks used by
95 times().
96
98 A limitation of the Linux system call conventions on some architectures
99 (notably i386) means that on Linux 2.6 there is a small time window (41
100 seconds) soon after boot when times() can return -1, falsely indicating
101 that an error occurred. The same problem can occur when the return
102 value wraps past the maximum value that can be stored in clock_t.
103
105 time(1), getrusage(2), wait(2), clock(3), sysconf(3), time(7)
106Linux man-pages 6.05 2023-03-30 times(2)