How do I monitor Linux/BSD system over time without scrolling output?

Suppose you would like to monitor memory utilization over time without having to look at scrolling output or disk space without scrolling output then normal commands do not provide any options.

You need to use watch command, which execute a program periodically, showing output in fullscreen mode. It runs command repeatedly, displaying its output. This allows you to watch the program output change over time. By default, the program is run every 2 seconds.

To watch memory usage:

$ watch free -m

Run free –m program is run every 5 seconds:

$ watch -n 5 free -m

To watch disk space usage:

$ watch df -h

To watch the contents of a directory change, you could use:

$ watch -d ls –l

Options:

• The -d flag will highlight the differences between successive updates.
• The –n {SECOND} flag use to specify a different interval.

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