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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXIT STATUS | ENVIRONMENT | GNU VERSION | BUGS | SEE ALSO | COLOPHON |
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time(1) General Commands Manual time(1)
time - time a simple command or give resource usage
time [option ...] command [argument ...]
The time command runs the specified program command with the given
arguments. When command finishes, time writes a message to
standard error giving timing statistics about this program run.
These statistics consist of (i) the elapsed real time between
invocation and termination, (ii) the user CPU time (the sum of the
tms_utime and tms_cutime values in a struct tms as returned by
times(2)), and (iii) the system CPU time (the sum of the tms_stime
and tms_cstime values in a struct tms as returned by times(2)).
Note: some shells (e.g., bash(1)) have a built-in time command
that provides similar information on the usage of time and
possibly other resources. To access the real command, you may
need to specify its pathname (something like /usr/bin/time).
-p When in the POSIX locale, use the precise traditional
format
"real %f\nuser %f\nsys %f\n"
(with numbers in seconds) where the number of decimals in
the output for %f is unspecified but is sufficient to
express the clock tick accuracy, and at least one.
If command was invoked, the exit status is that of command.
Otherwise, it is 127 if command could not be found, 126 if it
could be found but could not be invoked, and some other nonzero
value (1–125) if something else went wrong.
The variables LANG, LC_ALL, LC_CTYPE, LC_MESSAGES, LC_NUMERIC, and
NLSPATH are used for the text and formatting of the output. PATH
is used to search for command.
Below a description of the GNU 1.7 version of time. Disregarding
the name of the utility, GNU makes it output lots of useful
information, not only about time used, but also on other resources
like memory, I/O and IPC calls (where available). The output is
formatted using a format string that can be specified using the -f
option or the TIME environment variable.
The default format string is:
%Uuser %Ssystem %Eelapsed %PCPU (%Xtext+%Ddata %Mmax)k
%Iinputs+%Ooutputs (%Fmajor+%Rminor)pagefaults %Wswaps
When the -p option is given, the (portable) output format is used:
real %e
user %U
sys %S
The format string
The format is interpreted in the usual printf(3)-like way.
Ordinary characters are directly copied, tab, newline, and
backslash are escaped using \t, \n, and \\, a percent sign is
represented by %%, and otherwise % indicates a conversion. The
program time will always add a trailing newline itself. The
conversions follow. All of those used by tcsh(1) are supported.
Time
%E Elapsed real time (in [hours:]minutes:seconds).
%e (Not in tcsh(1).) Elapsed real time (in seconds).
%S Total number of CPU-seconds that the process spent in
kernel mode.
%U Total number of CPU-seconds that the process spent in user
mode.
%P Percentage of the CPU that this job got, computed as (%U +
%S) / %E.
Memory
%M Maximum resident set size of the process during its
lifetime, in Kbytes.
%t (Not in tcsh(1).) Average resident set size of the
process, in Kbytes.
%K Average total (data+stack+text) memory use of the process,
in Kbytes.
%D Average size of the process's unshared data area, in
Kbytes.
%p (Not in tcsh(1).) Average size of the process's unshared
stack space, in Kbytes.
%X Average size of the process's shared text space, in Kbytes.
%Z (Not in tcsh(1).) System's page size, in bytes. This is a
per-system constant, but varies between systems.
%F Number of major page faults that occurred while the process
was running. These are faults where the page has to be
read in from disk.
%R Number of minor, or recoverable, page faults. These are
faults for pages that are not valid but which have not yet
been claimed by other virtual pages. Thus the data in the
page is still valid but the system tables must be updated.
%W Number of times the process was swapped out of main memory.
%c Number of times the process was context-switched
involuntarily (because the time slice expired).
%w Number of waits: times that the program was context-
switched voluntarily, for instance while waiting for an I/O
operation to complete.
I/O
%I Number of filesystem inputs by the process.
%O Number of filesystem outputs by the process.
%r Number of socket messages received by the process.
%s Number of socket messages sent by the process.
%k Number of signals delivered to the process.
%C (Not in tcsh(1).) Name and command-line arguments of the
command being timed.
%x (Not in tcsh(1).) Exit status of the command.
GNU options
-f format, --format=format
Specify output format, possibly overriding the format
specified in the environment variable TIME.
-p, --portability
Use the portable output format.
-o file, --output=file
Do not send the results to stderr, but overwrite the
specified file.
-a, --append
(Used together with -o.) Do not overwrite but append.
-v, --verbose
Give very verbose output about all the program knows about.
-q, --quiet
Don't report abnormal program termination (where command is
terminated by a signal) or nonzero exit status.
GNU standard options
--help Print a usage message on standard output and exit
successfully.
-V, --version
Print version information on standard output, then exit
successfully.
-- Terminate option list.
Not all resources are measured by all versions of UNIX, so some of
the values might be reported as zero. The present selection was
mostly inspired by the data provided by 4.2 or 4.3BSD.
GNU time version 1.7 is not yet localized. Thus, it does not
implement the POSIX requirements.
The environment variable TIME was badly chosen. It is not unusual
for systems like autoconf(1) or make(1) to use environment
variables with the name of a utility to override the utility to be
used. Uses like MORE or TIME for options to programs (instead of
program pathnames) tend to lead to difficulties.
It seems unfortunate that -o overwrites instead of appends. (That
is, the -a option should be the default.)
Mail suggestions and bug reports for GNU time to [email protected].
Please include the version of time, which you can get by running
time --version
and the operating system and C compiler you used.
bash(1), tcsh(1), times(2), wait3(2)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.15 2025-05-17 time(1)
Pages that refer to this page: strace(1), times(2), time(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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