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
particular, 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 possible range of type clock_t. On error, (clock_t) -1 is returned, and errno is set appropriately.
ERRORS
EFAULT tms points outside the process's address space.
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
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 It is obsolete now.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 automatically
included in the tms_cstime and tms_cutime fields, although POSIX.1-2001
says that this should happen only 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 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 measure changes in elapsed time,
use clock_gettime(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 past the maximum value that can be stored in clock_t.
SEE ALSO
time(1), getrusage(2), wait(2), clock(3), sysconf(3), time(7)
COLOPHON
This page is part of release 4.09 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
Opportunity
Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.
Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.
Free Software
Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.
Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.
Free Books
The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.
Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.
Education
Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.
Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.
