Master Real-Time System Monitoring with Linux’s watch Command

watch Command Syntax

The watch utility repeatedly runs a specified command at fixed intervals and updates the terminal with its output. By default it executes the command every two seconds until interrupted with Ctrl+C.

watch <options> <command>

Run a Command Every X Seconds

Use the -n option followed by the number of seconds to change the refresh interval. watch -n 5 <command> Example: list a directory every two seconds.

watch ls -l ~/

Highlight Changes Between Updates

The -d option highlights differences between the previous and current output, making it easy to spot changes.

watch -d <command>

Hide Header

By default, watch shows a header with the interval, command, and timestamp. Suppress it with -t.

watch -t <command>

Beep on Errors

The -b option triggers a beep when the monitored command exits with a non‑zero status. This requires the beep package to be installed.

watch -b sudo systemctl status sshd.service

Exit When Output Changes

Use the -g option to make watch terminate as soon as the command’s output changes.

Example: wait for a specific file to appear.

watch -g "ls -l | grep filename" && echo "file arrived"

Example: notify when a user logs in.

watch -g "who | grep username" && echo "username logged in"

Monitor System Activity

The watch command can be combined with other Linux utilities (e.g., top, df, netstat) to continuously observe system resources, file changes, or user activity, reducing the need to manually re‑run commands.