How to Block 'su' Access for Sudo Users

In UNIX/Linux, su is the most powerful command that allows you to access the root account or another user’s account with their account password.

Although you can easily restrict or disable su command access for a specific user with sudo privileges by following the steps in this article.

Tutorial Details

Description	Block ‘su’ Access to Sudo Users
Difficulty Level	Moderate
Root or Sudo Privileges	Yes
Host System and Architecture	Ubuntu 22.10 (x64)
OS Compatibility	Ubuntu, Manjaro, Fedora, etc.
Prerequisites	visudo
Internet Required	No
Discussed Tools in this Article	nano

You need to modify the “/etc/sudoers” file in order to prevent or block sudo users from accessing the su command.

Also Read: Difference Between Su, Sudo Su, Sudo -i, and Sudo -s

But first, take a backup of this file using the following command:

$ sudo cp /etc/sudoers /etc/sudoers.bak

And then open the file using any of the following commands:

$ sudo visudo

#OR

$ sudo nano /etc/sudoers

Create the following alias under the “#Cmnd alias specification“ comment section.

Cmnd_Alias DISABLE_SU = /bin/su

Output:

Then add the following line at the end of the file, replacing “linuxtldr” with the actual username.

linuxtldr ALL=ALL, !DISABLE_SU

Output:

Save and close the file, then restart the current session to reflect the changes.

Also Read: How to Switch to Root or Normal User Account in Linux

Next time, when you try to access the su command using sudo, you will be prompted with the following error:

That’s all for now; sayonara.