watch Command: Tutorial & Examples
Run a program in regular intervals
watch command is a powerful tool in the Linux system. It allows you to continuously execute a
program or command at regular intervals and monitor the output in your terminal. This is particularly useful when you
want to keep an eye on a process, monitor system resources, or watch for specific changes in output.
watch command works by executing a specified command or script at regular intervals, the default being every 2
seconds. It then displays the output of the command to the terminal, clearing the screen and refreshing the output each
It does this by making use of the shell to execute the command, then displays the output. This process is repeated at the specified interval, giving you a live look at the output of your command.
watch command can be used in a wide variety of scenarios. Here are a few examples:
Track changes in a directory: You can use
lscommand to monitor changes in a directory's content.
Monitor network activity: The
watchcommand can be paired with commands like
netstatto observe live network activity on your server.
How to Use
watch is fairly straightforward. It follows this basic syntax:
watch [options] command
Here are a few examples of how to use
To watch the contents of a directory, you could use:
watch ls /path/to/directory
To monitor free memory on your system, you can use:
watch free -m
To monitor active network connections, you can use:
watch netstat -tup
Each of these commands will execute the specified command every 2 seconds, and display the output to your terminal.
Common Command Parameters
Here are some common parameters you might use with
--interval: This allows you to specify the interval at which
watchwill execute your command. For example,
watch -n 5 free -mwill execute
free -mevery 5 seconds.
--differences: This tells
watchto highlight differences between successive updates.
watch -d ls /path/to/directorywill show you when changes are made to the specified directory.
--help: Displays the help message and exits.
Potential Problems and Pitfalls
watch is a powerful tool, it's important to be aware of a few potential issues:
Overuse: Executing a command too frequently can cause unnecessary load on your system. Be sure to use an appropriate interval.
Terminal size: If the output of your command is too large for your terminal, it can make the output hard to read. You may need to adjust your terminal size or the command you are using.
Long running commands: If the command you are watching takes longer to execute than the interval you've set,
watchwill start another instance of the command before the first has finished. This can lead to unpredictable results or increased system load.
watch command is a powerful tool for monitoring and debugging on your Linux server. By understanding how it works
and how to use it effectively, you can gain greater insight into your system and solve common problems more effectively.