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Restrict the use of su command

su is used to become another user during a login session. Invoked without a username, su defaults to becoming the super user. The user will be prompted for a password, if appropriate. Invalid passwords will produce an error message. All attempts, both valid and invalid, are logged to detect abuses of the system.

By default almost all distro allows to use su command. However you can restrict the use of su command for security reasons.

Both UNIX and Linux have a group called wheel. If user is member of this group she can use su command. We can add user to this group.

For example add existing user rocky to wheel group
# usermod -G wheel rocky

Now open /etc/pam.d/su PAM config file:
# vi /etc/pam.d/su
Append line as follows:
auth required /lib/security/pam_wheel.so use_uid
auth required pam_wheel.so use_uid

Save and close the file.

Because of above setting only members of the administrative group wheel can use the su command. However I still recommend sudo over su for better control, security and ease of use. This is also default behavior on FreeBSD.

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{ 6 comments… add one }

  • Vasudeva April 18, 2008, 8:31 pm

    Can we restrict multiple users using su command at a time ? Like user1 already using su – and working on some commands. Can we disallow using user2 at the same time ? Please let me know how can we configure this ?

  • ardmad July 9, 2009, 6:07 pm

    Hi. Can you tell me how or in what interface should i type:

    $ su root

    I don’t quite understand where to type that. Thanks.

  • jalal hajigholamali August 17, 2011, 3:36 pm

    thanks a lot.
    any history about wheel, why they choose wheel ?

  • Ankit August 29, 2011, 11:34 am

    Great tip, now i have blocked the root ssh login and also allowed particular user to use su. :)

    Thanks a lot for this tip.


  • alpha July 31, 2013, 3:45 am

    You will be able to issue “su -” and get a login shell if you only edit /etc/pam.d/su, you need to edit /etc/pam.d/su-l as well.

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