Say you’re helping someone on their computer, where you are also a user, and want to access something like your .bash_profile in order to properly assist them. Logging them out to log you in would be ridiculously frustrating, and unfortunately no other computers are around for you to access the system through an ssh connection. Never fear! To access your files through the command line, without going through sudo 12 times, you can continue using the Terminal as yourself after switching users. This is done through the su command.

alice@computer $ su bob
Password:

This time, you only get one attempt, before you get hit with “su: Sorry.”

It is worth noting that the default use of su without a specified user is to switch to the root user. (You can read more about that in UNIX systems)