Switch User “su” Command in Linux with Useful Examples

The su command is also known as switch user. This command is used to become another user during a login session. When invoked without a username, su defaults switch to the superuser. Basically, the su command is used to change the currently logged-in user to another user without logging out from the system.

It is a frequently used command mostly by Linux terminal users. This tutorial will help you understand the uses of the Linux su command with examples.

Syntax:

su [OPTIONS] [USER] [OPTIONAL ARGS...]

su Command Examples in Linux

Let’s begin with a basic example. I’m Logged in to my system with user ‘root’, verified the identity using whoami command.

whoami

Output:

mytechmint

Then switch to root user with su command. Again verified the identity.

su - root
whoami

Output:

root

Things to Know:

• Invoke the su command without username becomes the superuser (root).
• Using hyphen (-) with switching invoke login shell scripts. This is used to provide an environment similar to what the user got at direct login
• The current environment is passed to the new shell with effective environment variables to switch users.

The sudo privileged users can also prefix sudo with su command. like:

sudo su - root 

Sometimes, you may only need to switch user to run a single or few commands only. In that condition, su provides you -c the option to run the command as another user without actually switching the shell.

su - root -c "whoami"

Output:

root

“su” Command Line Options

Linux su command has only a few but very useful options. These options are very useful while automating tasks with shell scripts.

1. 1. -c, --command Use this option to pass command to the invoked shell. With the help of this, you can run the command as another user.
   2. -, -l, --login make the new shell a login shell. So all the environments will be set as similar to users logged-in directly.
   3. -s, --shell Change the default SHELL that is specified in “/etc/passwd” file.
   4. -m, -p, --preserve-environment Use this option to preserve environment variables, This is helpful while running the command temporarily as another user.

For “su” command help page use the below command.

su --help

For “su” command manual page use the below command.

man su