If you’re managing a Linux server, it’s good to be ready with a number of commands that you can use to check user activity – when your users are logging in and how often, what groups they belong to, how much disk space they’re consuming, what command they’re running, how much disk space they’re occupying, if they’re reading their mail and more. Here are some commands to help you do that.

Source: LXer – How to assess user activity in Linux