# Time (Unix)

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{{short description|Command in Unix and Unix-like operating systems}}
{{about|the Unix command|Unix's means of representing points in time|Unix time|the Unix function call|time.h}}
{{lowercase title}}
{{Infobox software
| name                   = time
| logo                   = 
| screenshot             = Time-example-command.gif
| screenshot size        = 
| caption                = Example of <code>time</code> command
| developer              = Various [open-source](/source/open-source_software) and [commercial](/source/commercial_software) developers
| released               = 
| latest release version = 
| latest release date    = 
| operating system       = [Unix](/source/Unix), [Unix-like](/source/Unix-like), [Inferno](/source/Inferno_(operating_system))
| platform               = [Cross-platform](/source/Cross-platform)
| genre                  = [Command](/source/Command_(computing))
| license                = 
| website                = 
}}
In [computing](/source/computing), <code>'''time'''</code> is a command in [Unix](/source/Unix) and [Unix-like](/source/Unix-like) operating systems. It is used to determine the duration of execution of a particular [command](/source/command_(computing)).

==Overview==
<code>time(1)</code> can exist as a standalone program (such as [GNU](/source/GNU) time) or as a [shell](/source/Unix_shell) builtin in most cases (e.g. in [sh](/source/Unix_shell), [bash](/source/Bash_(Unix_shell)), [tcsh](/source/tcsh) or in [zsh](/source/zsh)).

===User time vs system time===
The total CPU time is the combination of the amount of time the CPU or CPUs spent performing some action for a program and the amount of time they spent performing [system call](/source/system_call)s for the [kernel](/source/kernel_(operating_system)) on the program's behalf. When a program loops through an array, it is accumulating user CPU time. Conversely, when a program executes a [system call](/source/system_call) such as <code>exec</code> or <code>fork</code>, it is accumulating system CPU time.

===Real time vs CPU time===
The term "real time" in this context refers to elapsed [wall-clock time](/source/wall-clock_time), like using a stop watch. The total CPU time (user time + sys time) may be more or less than that value. Because a program may spend some time waiting and not executing at all (whether in user mode or system mode) the real time may be greater than the total CPU time. Because a program may fork children whose CPU times (both user and sys) are added to the values reported by the <code>time</code> command, but on a multicore system these tasks are run in parallel, the total CPU time may be greater than the real time.

==Usage==
To use the command, one simply precedes any command by the word <code>time</code>, such as:
<syntaxhighlight lang="bash">$ time ls</syntaxhighlight>

When the command completes, <code>time</code> will report how long it took to execute the <code>[ls](/source/ls)</code> command in terms of user [CPU time](/source/CPU_time), system CPU time, and real time. The output format varies between different versions of the command, and some give additional statistics, as in this example:
<syntaxhighlight lang="console">
$ time host wikipedia.org
wikipedia.org has address 103.102.166.224
wikipedia.org mail is handled by 50 mx2001.wikimedia.org.
wikipedia.org mail is handled by 10 mx1001.wikimedia.org.
host wikipedia.org  0.04s user 0.02s system 7% cpu 0.780 total
$
</syntaxhighlight>

A simple [stopwatch](/source/stopwatch) ({{key|Ctrl|d}} to stop):
<syntaxhighlight lang="console">
$ time read

real    0m9.760s
user    0m0.000s
sys     0m0.000s
$
</syntaxhighlight>

{{mono|time}} (either a standalone program, or when Bash shell is running in POSIX mode AND {{mono|time}} is invoked as <code>time -p</code>) reports to standard error output.

===time -p===
Portable scripts should use <code>time -p</code> mode, which uses a different output format, but which is consistent with various implementations:
<syntaxhighlight lang="console">
$ time -p sha256sum /bin/ls
12477deb0e25209768cbd79328f943a7ea8533ece70256cdea96fae0ae34d1cc  /bin/ls
real 0.00
user 0.00
sys 0.00
$
</syntaxhighlight>

==Implementations==
Depending on the shell the {{mono|time}} command defaults to being treated as either a shell keyword, [builtin](/source/Shell_builtin) or binary executable. One can also force the use of  the binary by referencing the file directly, ie: '''/usr/bin/time''' anyCommmand.  To  determine the default, issue the command: <code>'''type time'''</code>.<ref>{{Cite web |title=Linux  Time Command |url=https://linuxize.com/post/linux-time-command/ |access-date=July 24, 2025 |website=Linuxize |archive-date=July 22, 2025 |archive-url=https://web.archive.org/web/20250722101559/https://linuxize.com/post/linux-time-command/ |url-status=live }}</ref>

===GNU time===
Current versions of GNU time, report more than just a time by default:
<syntaxhighlight lang="console">
$ /usr/bin/time sha256sum /bin/ls
12477deb0e25209768cbd79328f943a7ea8533ece70256cdea96fae0ae34d1cc  /bin/ls
0.00user 0.00system 0:00.00elapsed 100%CPU (0avgtext+0avgdata 2156maxresident)k
0inputs+0outputs (0major+96minor)pagefaults 0swaps
$
</syntaxhighlight>

Format of the output for [GNU](/source/GNU) time, can be adjusted using <code>'''TIME'''</code> environment variable, and it can include information other than the execution time (i.e. memory usage). This behavior is not available in general [POSIX](/source/POSIX)-compliant time, or when executing as <code>time -p</code>.

The binary version sends its output to [stderr](/source/stderr) instead of [stdout](/source/stdout) but this can be overridden by using the <code>-o ''filename''</code> or <code>--output ''filename''</code> flags.

Documentation of this {{mono|time}} can be usually accessed using <code>man 1 time</code>.

====Method of operation====
According to the source code of the GNU implementation of <code>time</code>, most information shown by <code>time</code> is derived from the <code>wait3</code> system call. On systems that do not have a <code>wait3</code> call that returns status information, the <code>times</code> system call is used instead.

===Bash===
In a popular Unix shell [Bash](/source/Bash_(Unix_shell)), <code>'''time'''</code> is a special keyword, that can be put before a [pipeline](/source/Pipeline_(Unix)) (or single command), that measures time of entire pipeline, not just a singular (first) command, and uses a different default format, and puts empty line before reporting times:
<syntaxhighlight lang="console">
$ time seq 10000000 | wc -l
10000000

real	0m0.078s
user	0m0.116s
sys	0m0.029s
$
</syntaxhighlight>

The reported time is a time used by both <code>'''seq'''</code> and <code>'''wc -l'''</code> added up. Format of the output can be adjusted using <code>'''TIMEFORMAT'''</code> variable.

When the {{mono|time}} is treated as a special keyword, it also ignores pipeline redirections even when executed as <code>time -p</code>.  The work around is to enclose the command group in braces, ie: <code>{ time ''anyCommand''; } 2> timing.Output</code><ref>{{cite web| first=Burak| last=Gökmen| title=Redirecting the Output of the time Command| date=June 16, 2025| access-date=July 24, 2025| url=https://www.baeldung.com/linux/redirect-time-output| publisher=Baeldung| archive-date=September 13, 2025| archive-url=https://web.archive.org/web/20250913020016/https://www.baeldung.com/linux/redirect-time-output| url-status=live}}</ref>  Alternatively one could set the bash shell to run in "POSIX mode" can force the shell to ignore the reserved keyword implementation if an optional flag follows the {{mono|time}} command.<ref>{{cite web | publisher=gnu.or | title=Bash POSIX Mode | date=July 26, 2025 | access-date=July 28, 2025 | url=https://www.gnu.org/software/bash/manual/html_node/Bash-POSIX-Mode.html#Bash-POSIX-Mode-1 | archive-date=June 13, 2023 | archive-url=https://web.archive.org/web/20230613061206/https://www.gnu.org/software/bash/manual/html_node/Bash-POSIX-Mode.html#Bash-POSIX-Mode-1 | url-status=live }}</ref>

Documentation of {{mono|time}} can be accessed using <code>man 1 bash</code>, or within bash itself using <code>help time</code>.

==See also==
{{Wikibooks|Guide to Unix|Commands}}
* [System time](/source/System_time)
* [Cron](/source/Cron) process for scheduling jobs to run at a particular time
* [TIME (command)](/source/TIME_(command))

==References==
{{Reflist}}
* {{man|cu|time|SUS|time a simple command}}
* {{man|1|time|Inferno}}
* {{man|1|time|Linux|time a simple command or give resource usage}}

{{Unix commands}}

Category:Unix SUS2008 utilities
Category:Unix process- and task-management-related software
Category:Inferno (operating system) commands

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Adapted from the Wikipedia article [Time (Unix)](https://en.wikipedia.org/wiki/Time_(Unix)) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Time_(Unix)?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.