times(3) [netbsd man page]
TIMES(3) BSD Library Functions Manual TIMES(3) NAME
times -- process times LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <sys/times.h> clock_t times(struct tms *tp); DESCRIPTION
This interface is obsoleted by getrusage(2) and gettimeofday(2). The times() function returns the value of time in clock ticks since 0 hours, 0 minutes, 0 seconds, January 1, 1970, Coordinated Universal Time (UTC). The number of clock ticks per second may be determined by calling sysconf(3) with the _SC_CLK_TCK request. It is generally (but not always) between 60 and 1024. Note that at the common rate of 100 ticks per second on many NetBSD ports, and with a 32-bit unsigned clock_t, this value first wrapped in 1971. The times() call also fills in the structure pointed to by tp with time-accounting information. The tms structure is defined as follows: typedef struct { clock_t tms_utime; clock_t tms_stime; clock_t tms_cutime; clock_t tms_cstime; } The elements of this structure are defined as follows: tms_utime The CPU time charged for the execution of user instructions. tms_stime The CPU time charged for execution by the system on behalf of the process. tms_cutime The sum of the tms_utime s and tms_cutime s of the child processes. tms_cstime The sum of the tms_stimes and tms_cstimes of the child processes. All times are measured in clock ticks, as defined above. Note that at 100 ticks per second, and with a 32-bit unsigned clock_t, the values wrap after 497 days. The times of a terminated child process are included in the tms_cutime and tms_cstime elements of the parent when one of the wait(2) func- tions returns the process ID of the terminated child to the parent. If an error occurs, times() returns the value ((clock_t)-1), and sets errno to indicate the error. ERRORS
The times() function may fail and set the global variable errno for any of the errors specified for the library routines getrusage(2) and gettimeofday(2). SEE ALSO
time(1), getrusage(2), gettimeofday(2), wait(2), sysconf(3) STANDARDS
The times() function conforms to ISO/IEC 9945-1:1990 (``POSIX.1''). BSD
June 4, 1993 BSD
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TIMES(2) Linux Programmer's Manual TIMES(2) NAME
times - get process times SYNOPSIS
#include <sys/times.h> clock_t times(struct tms *buf); DESCRIPTION
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) are added in at the moment wait(2) or waitpid(2) returns their process ID. In par- ticular, times of grandchildren that the children did not wait for are never seen. All times reported are in clock ticks. RETURN VALUE
times() returns the number of clock ticks that have elapsed since an arbitrary point in the past. The return value may overflow the possi- ble range of type clock_t. On error, (clock_t) -1 is returned, and errno is set appropriately. CONFORMING TO
SVr4, 4.3BSD, POSIX.1-2001. NOTES
The number of clock ticks per second can be obtained using: sysconf(_SC_CLK_TCK); In POSIX.1-1996 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 automati- cally included in the tms_cstime and tms_cutime fields, although POSIX.1-2001 says that this should only happen if the calling process wait(2)s on its children. This nonconformance 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 behavior, and most other Unix implementations require a non-NULL value for buf. Note that clock(3) also returns a value of type clock_t, but this value is measured in units of CLOCKS_PER_SEC, not the clock ticks used by times(). On Linux, the "arbitrary point in the past" from which the return value of times() is measured has varied across kernel versions. On 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. This variability across kernel versions (and across Unix implementations), combined with the fact that the returned value may overflow the range of clock_t, means that a portable application would be wise to avoid using this value. To mea- sure changes in elapsed time, use gettimeofday(2) instead. Historical 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. BUGS
A limitation of the Linux system call conventions on some architectures (notably i386) means that on Linux 2.6 there is a small time window (41 seconds) soon after boot when times() can return -1, falsely indicating that an error occurred. The same problem can occur when the return value wraps passed the maximum value that can be stored in clockid_t. SEE ALSO
time(1), getrusage(2), wait(2), clock(3), sysconf(3), time(7) COLOPHON
This page is part of release 3.25 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. Linux 2008-06-25 TIMES(2)