times() - Unix, Linux System Call
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times() - Unix, Linux System Call

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times - get process times


#include <sys/times.h>

clock_t times(struct tms *buf);


times() stores the current process times in the struct tms that buf points to. The struct tms is as defined in <sys/times.h>:

struct tms {
clock_t tms_utime;  /* user time */
clock_t tms_stime;  /* system time */
clock_t tms_cutime; /* user time of children */
clock_t tms_cstime; /* system time of children */

The tms_utime field contains the CPU time spent executing instructions of the calling process. The tms_stime field contains the CPU time spent in the system while executing tasks on behalf of the calling process. The tms_cutime field contains the sum of the tms_utime and tms_cutime values for all waited-for terminated children. The tms_cstime field contains the sum of the tms_stime and tms_cstime values for all waited-for terminated children.

Times for terminated children (and their descendants) is added in at the moment wait(2) or waitpid(2) returns their process ID. In particular, times of grandchildren that the children did not wait for are never seen.

All times reported are in clock ticks.


times() returns the number of clock ticks that have elapsed since an arbitrary point in the past. For Linux 2.4 and earlier this point is the moment the system was booted. Since Linux 2.6, this point is (2^32/HZ) - 300 (i.e., about 429 million) seconds before system boot time. The return value may overflow the possible range of type clock_t. On error, (clock_t) -1 is returned, and errno is set appropriately.


The number of clock ticks per second can be obtained using sysconf(_SC_CLK_TCK); In POSIX-1996 the symbol CLK_TCK (defined in <time.h>) is mentioned as obsolescent. It is obsolete now.

In Linux kernel versions before 2.6.9, if the disposition of SIGCHLD is set to SIG_IGN then the times of terminated children are automatically included in the tms_cstime and tms_cutime fields, although POSIX.1-2001 says that this should only happen if the calling process wait()s on its children. This non-conformance is rectified in Linux 2.6.9 and later.

On Linux, the buf argument can be specified as NULL, with the result that times() just returns a function result. However, POSIX does not specify this behaviour, and most other Unix implementations require a non-NULL value for buf.

Note that clock(3) returns values of type clock_t that are not measured in clock ticks but in CLOCKS_PER_SEC.


SVr4, 4.3BSD, POSIX.1-2001.


SVr1-3 returns long and the struct members are of type time_t although they store clock ticks, not seconds since the epoch. V7 used long for the struct members, because it had no type time_t yet.

On older systems the number of clock ticks per second is given by the variable HZ.


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