Understand the usage of the watch program in Linux.


  1. Linux OS Server (preferably CentOS or any other rpm-based distros)


Step 1: Install Watch Tool

If the watch command does not exist in your Linux OS machine, you can install the procps package.

For rpm-based distros: –

yum install -y procps

For debian-based distros: –

apt-get install procps

Step 2: Understanding Watch

The watch command is an effective tool used to allow commands to be run in a periodical manner. In order words, this is extremely useful if you wish to monitor changes in the results of an executed command in a terminal window.

To use the command to monitor the memory usage, simply type: –

watch free -m

You will be directed to a terminal windows where the free program will be run every 2 seconds by default.

Step 3: Other Useful Options

If you wish to change the number of seconds between updates, use the -n or –internal options to specify a different time frame.

In the example below, we specify the watch command to run the free program every 1 second.

watch -n 1 free -m


watch --interval 1 free -m

You can also highlight the differences between updates by running the -d or –difference option.

In the example below, we use the -d option to note the changes in the system uptime.

watch -d uptime


watch --difference uptime

You can also automatically exit the watch command after a change has been detected with the -g or –chgexit option.

In the example below, the system will exit the watch command after any changes in memory usage is detected.

watch -g free -m


watch --chgexit free -m

To check the version of the watch program, simply use the -v option.

watch -v

To know what other options are available within the watch tool, you can use the -h option to retrieve the user manual.

watch -h