Remove a users right to use sudo [duplicate]

Only users in the sudo group may use the sudo command. To remove the user jdoe from the group sudo type (as root):

deluser jdoe sudo

If you are not root, type

sudo deluser jdoe sudo

Reference: How to remove a user from a group?

Update

As pointed out by @Aleks G in a comment the above is only half the truth:

By default only members of the sudo group may run commands with sudo <command>. This is accomplished by the line

#  who  where    as-whom  what
  %sudo  ALL  = (ALL:ALL) ALL

in the /etc/sudoers file. It means:

• members of the group sudo (who) may run
• on any computer (where)
• as any user and any group (as-whom)
• any command (what)

This is the default setup on Ubuntu and hence adding or removing a user to/from the group sudo gives or revokes the privilege to run commands with sudo <command>.

But it is also possible to add other groups and/or users to the /etc/sudoers file (or below /etc/sudoers.d/) like so:

alice  myhost  = (bob) /bin/ls

This means: user alice may run /bin/ls as user bob but only on host myhost.

alice could now do sudo -u bob ls /home/bob. This is independant of a membership in the sudo group. If you have such a setup, then it is not sufficient to remove alice from the sudo group. Instead you need to remove the alice line from the /etc/sudoers file.

The where part is only relevant if you share the sudoers file across different computers and want to keep it the same on every computer.

The answer regarding the sudo group is correct for most situations. There is another way to give a user sudo rights, and that is to add their username directly to the sudoers file. If the username has been added, then it must be removed from that file -- Usually the entire line containing the username. This is not a common scenario, but is possible. To edit the sudoers file, use visudo.