Linux how to use time

Linux / Unix: time Command Examples

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. This page explains time command in Linux and Unix-like system with most common examples.

time command details
Description	Report time consumed by command execution
Category	Processes Management
Difficulty	Easy
Root privileges	No
Est. reading time	4 minutes
Table of contents » Syntax » Examples » Redirect time output to file » GNU/Linux time command » Understanding TIMEFORMAT » Summing up

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

Purpose

Run command/programs or script and summarize system resource usage on your screen.

Syntax

The basic syntax is as follows:
time command
time command arg1 arg2 . argN
time [options] command arg1 arg2 . argN

Is my time command shell built-in or external command?

The time command is also built into the BASH/KSH/CSH/TCSH with a different syntax. Let us use the type command or command command to verify location:
type -a time
command -V time

To run the time command while in the shells, type:
/usr/bin/time -p command
/bin/time -p command arg1 arg2
Users of the bash or ksh shell need to use an explicit path in order to run the external time command and not the shell builtin variant.

time command examples

To measure the time required to run a program called date, enter:
$ time date
To use external time command give full path to time binary:
$ /usr/bin/time -p date

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:

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

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

Using time command on my Linux system

Use FORMAT as the format string that controls the output of time

Table 1: Formatting the output of /usr/bin/time

FORMAT	Description
%	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.

Using time command on Linux or Unix with formatting

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:

See percentage of CPU used by your command:
/usr/bin/time -f «CPU Percentage: %P» command
/usr/bin/time -f «CPU Percentage: %P» grep vivek /etc/passwd
/usr/bin/time -f «CPU Percentage: %P» find /etc/ -type f -iname «a*.conf»
CPU Percentage: 76%

Understanding TIMEFORMAT used by bash’s buitin time

The value of TIMEFORMAT parameter is used as a format string specifying how the timing information for pipelines prefixed with the time reserved word should be displayed. The % character introduces an escape sequence that is expanded to a time value or other information. The escape sequences and their meanings are as follows; the braces denote optional portions.

Table 2: TIMEFORMAT parameter values

Value	Description
%%	A literal %.
%[p][l]R	The elapsed time in seconds.
%[p][l]U	The number of CPU seconds spent in user mode.
%[p][l]S	The number of CPU seconds spent in system mode.
%P	The CPU percentage, computed as (%U + %S) / %R.

The optional p is a digit specifying the precision, the number of fractional digits after a decimal point. A value of 0 causes no decimal point or fraction to be output. At most three places after the decimal point may be specified; values of p greater than 3 are changed to 3. If p , is not specified, the value 3 is used. The optional l specifies a longer format, including minutes, of the form MMmSS.FFs . The value of p determines whether or not the fraction is included.

How to use bash’s builtin time command in Linux / Unix

The syntax is almost same:
time command
time ls
TIMEFORMAT=»%P» time ls
TIMEFORMAT=»%U» time sleep 3
TIMEFORMAT=»%S» time sleep 3
TIMEFORMAT=»%R» time sleep 2

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Summing up

You learned about the time command that reports the time consumed by the pipeline’s execution. It will summarize system resource usage on the screen. The syntax of time might change on your local Unix or Linux distro. Hence, to get help for builtin time command, type:
help time
# or read shell man page
man bash
For external time (/bin/time or /usr/bin/time) command, run:
man time

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How to Time a Command in Linux

If you want to be a good Linux administrator, therefore you should know time command. It is used to determine how long a given command takes to run.

It is useful for testing the performance of your scripts and commands (ie helps to find execution time for shell scripts or time taken for a command to finish).

How to Use Linux time command

To use time command, just execute time with the command/program you want to run as input. Please check below example

The real signifies the wall clock time the ‘ping’ command took from execution till termination, user and sys are the time taken by ping the user space and kernel space.

How to Make time command writes its output to a file

To write the time command output to a file instead of the print out screen, use the -o command line option, which expects a file name/path as input.

Now we will display ping’s output on stdout, while the time command output will be written to the text file.

Note: We used /usr/bin/time instead of time because the shell built-in time command doesn’t offer the -o option.

How to appends its output to an existent file

To append the time command output to an existent file instead of overwrite it, use the -a command line option.

How to get Detailed output of linux time command

We can use the -v command line option to produce detailed output.

How to customizing time command output

There are a large number of formatting options as shown in the following list

C — Name and command line arguments used
D — Average size of the process’s unshared data area in kilobytes
E — Elapsed time in a clock format
F — Number of page faults
I — Number of file system inputs by the process
K — Average total memory use of the process in kilobytes
M — Maximum resident set the size of the process during the lifetime in Kilobytes
O — Number of file system outputs by the process
P — Percentage of CPU that the job received
R — Number of minor or recoverable page faults
S — Total number of CPU seconds used by the system in kernel mode
U — Total number of CPU seconds used by user mode
W — Number of times the process was swapped out of main memory
X — Average amount of shared text in the process
Z — System’s page size in kilobytes
c — Number of times the process was context-switched
e — Elapsed real 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 time the process was context-switched voluntarily
x — Exit status of the command

We can use the formatting switches as follows:

The output for the above command would be something like this:

If we want to add a new line as part of the format string use the newline character as follows:

Linux Time Command Versions

There are three-time command Versions, Bash, Zsh and Gnu time command. We can use the type command to determine whether time is a binary or a built-in keyword.

Please write your suggestions or comments on time command and for more information use time man pages.

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Set Time/Date/Timezone in Ubuntu Linux

Time is an important aspect in Linux systems especially in critical services such as cron jobs. Having the correct time on the server ensures that the server operates in a healthy environment that consists of distributed systems and maintains accuracy in the workplace.

In this tutorial, we will focus on how to set time/date/time zone and to synchronize the server clock with your Ubuntu Linux machine.

Check Current Time

You can verify the current time and date using the date and the timedatectl commands. These linux commands can be executed straight from the terminal as a regular user or as a superuser. The commands are handy usefulness of the two commands is seen when you want to correct a wrong time from the command line.

Using the date command

Log in as a root user and use the command as follows

Output

You can also use the same command to check a date 2 days ago

Output

Using timedatectl command

Checking on the status of the time on your system as well as the present time settings, use the command timedatectl as shown

Changing Time

We use the timedatectl to change system time using the format HH:MM: SS. HH stands for the hour in 24-hour format, MM stands for minutes and SS for seconds.

Setting the time to 09:08:07 use the command as follows (using the timedatectl)

using date command

Changing time means all the system processes are running on the same clock putting the desktop and server at the same time. From the command line, use date command as follows

Where,
• 10: Hour (hh)
• 13: Minute (mm)
• 13: Second (ss)

To change the locale to either AM or PM use the %p in the following format.

Change Date

Generally, you want your system date and time is set automatically. If for some reason you have to change it manually using date command, we can use this command :

It will set your current date and time of your system into ‘January 25, 2014′ and ’09:17:00 AM’. Please note, that you must have root privilege to do this.

You can use timedatectl to set the time and the date respectively. The accepted format is ‘YYYY-MM-DD’, ‘YYYY’ represents the year, ‘MM’ the month in two digits and ‘DD’ for the day in two digits.

Changing the date to ’15 January 2019′, you should use the following command:

Create custom date format

To create custom date format, use a plus sign (+)

%D format follows Year/Month/Day format.

You can also put the day name if you want. Here are some examples :

List/Change time zone

Changing the time zone is crucial when you want to ensure that everything synchronizes with the Network Time Protocol. The first thing to do is to list all the region’s time zones using the list-time zones option or grep to make the command easy to understand

The above command will present a scrollable format.

Recommended timezone for servers is UTC as it doesn’t have daylight savings. If you know, the specific time zones set it using the name using the following command

To display timezone execute

Set the Local-rtc

The Real-time clock (RTC) which is also referred to as the hardware clock is independent of the operating system and continues to run even when the server is shut down.

Use the following command

In addition, the following command for the local time

Check/Change CMOS Time

The computer CMOS battery will automatically synchronize time with system clock as long as the CMOS is working correctly.

Use the hwclock command to check the CMOS date as follows

To synchronize the CMOS date with system date use the following format

Conclusion

To have the correct time for your Linux environment is critical because many operations depend on it. Such operations include logging events and cron jobs as well.

If you have any questions or feedback, feel free to leave a comment.

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