Linux / Unix: time Command Examples

Posted on in Categories , , , , last updated February 5, 2014
time command

I am new Linux and Unix systems user. How do I display the time of the execution of a command/script on Linux or Unix-like operating systems using shell prompt?

You need to use the time command to display the elapsed time during the execution of a command or script.

time command details
DescriptionReport time consumed by
command execution
Root privilegesNo
Estimated completion time10m
The time command show the following information on screen (on the standard error output, by default) about resources used by command:

  1. real time
  2. user time
  3. sys time


Run command/programs or script and summarize system resource usage


The basic syntax is as follows:

time command


time command arg1 arg2 ... argN


time [options] command arg1 arg2 ... argN

Note: The time command is also built into the BASH/KSH/CSH/TCSH with a different syntax. To run the time command while in the shells, type:

/usr/bin/time -p command
/usr/bin/time -p command arg1 arg2

time command examples

To measure the time required to run a program called date, enter:
$ time date
$ /usr/bin/time -p date
Sample outputs:
time command demo

How do I redirect time command output to a file?

The syntax is as follows to save a record of the time command information in a file called output.time.txt, run:

time date 2> output.time.txt
/usr/bin/time -p date 2> output.time.txt

If above command failed, try the following to save a record of the time command information in a file:

( time date ) 2> output.time.txt
## OR ##
{ time date ; } 2> output.time.txt

Use the cat command to display output on screen:
$ cat output.time.txt

A note about GNU/Linux time command

GNU/Linux user can use the following syntax to write the resource use statistics to file instead of to the standard error stream:
$ /usr/bin/time -o output.time.txt -p date
$ cat output.time.txt

Pass the -a option to append the resource use information to the output file instead of overwriting it. This option is only useful with the -o option:
$ /usr/bin/time -a -o output.time.txt -p sleep 2
$ cat output.time.txt

You can control time command output format using -f FORMAT as follows:
$ /usr/bin/time -f 'FORMAT' -p command
Use FORMAT as the format string that controls the output of time as follows:

 % A literal `%’.
 C Name and command line arguments of the command being timed.
 D Average size of the process’s unshared data area, in Kilobytes.
 E Elapsed real (wall clock) time used by the process, in [hours:]minutes:seconds.
 F Number of major, or I/O-requiring, page faults that occurred while the process was running. These are faults where the page has actually migrated out of primary memory.
 I Number of file system inputs by the process.
 K Average total (data+stack+text) memory use of the process, in Kilobytes.
 M Maximum resident set size of the process during its lifetime, in Kilobytes.
 O Number of file system outputs by the process.
 P Percentage of the CPU that this job got. This is just user + system times divided by the total running time. It also prints a percentage sign.
 R Number of minor, or recoverable, page faults. These are pages that are not valid (so they fault) 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.
 S Total number of CPU-seconds used by the system on behalf of the process (in kernel mode), in seconds.
 U Total number of CPU-seconds that the process used directly (in user mode), in seconds.
 W Number of times the process was swapped out of main memory.
 X Average amount of shared text in the process, in Kilobytes.
 Z System’s page size, in bytes. This is a per-system constant, but varies between systems.
 c Number of times the process was context-switched involuntarily (because the time slice expired).
 e Elapsed real (wall clock) time used by the process, in seconds.
 k Number of signals delivered to the process.
 p Average unshared stack size of the process, in Kilobytes.
 r Number of socket messages received by the process.
 s Number of socket messages sent by the process.
 t Average resident set size of the process, in Kilobytes.
 w Number of times that the program was context-switched voluntarily, for instance while waiting for an I/O operation to complete.
 x Exit status of the command.

In this example, show just the user, system, and total time using format option:
$ /usr/bin/time -f "%E real,%U user,%S sys" sleep 2
$ /usr/bin/time -f "%E real,%U user,%S sys" /path/to/script

Sample outputs:

0:02.00 real,0.00 user,0.00 sys
See also
CategoryList of Unix and Linux commands
File Managementcat
Network Utilitiesdighostip
Package Managerapt
Processes Managementbgchrootdisownfgjobskillkillallpwdxtimepidofpstree
User Informationgroupsidlastlastcommlognameuserswwhowhoamilidmembers

2 comment

  1. Why are we using /usr/bin/time? when not using any options simply writing time is working but when should we go for /usr/bin/time when using options? This is working but i dont understand the logic. when :
    time -o output.txt ls //is used i am getting error as no bash command -o
    /usr/bin/time -o output.txt ls //is working fine

    1. Got the answer. time simply referes to time command of bash which has no options. /usr/bin/time referes to the time command which this tutorial is speaking about. bash time command help: help time, normal time command help: man time

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