Sudo

Avoid modifying the sudoers files manually and execute visudo instead; it will check the syntax on save, preventing you from screwing up the file.

TL;DR

# Make changes to a sudoers file.
visudo
visudo -f path/to/file

# Check the syntax of a sudoers file.
visudo -c path/to/file

Drop privileges

# Invalidate the user's cached credentials.
sudo -k

# Ignore the user's cached credentials for the given command only.
sudo -k ls

Restrict permissions a little

# file /etc/sudoers.d/user
Cmnd_Alias UPGRADE_CMND  = /usr/bin/apt update, /usr/bin/apt list --upgradable, /usr/bin/apt upgrade
Cmnd_Alias SHUTDOWN_CMND = /sbin/shutdown
user ALL=(ALL:ALL) NOPASSWD: SHUTDOWN_CMND, UPGRADE_CMND

Avoid providing a password

# file /etc/sudoers.d/user
user ALL=(ALL:ALL) NOPASSWD: ALL

Execute commands as a specific user

Invoke a login shell using the -i, --login option. When one does not specify a command a login shell prompt is returned, otherwise the output of the command is returned:

% whoami
root
% sudo -i -u user
$ whoami
user

% sudo -i -u user whoami
user

Troubleshooting

I modified a sudoers file manually, messed it up, and now I cannot use sudo anymore

Should you see something similar to this when using sudo:

$ sudo visudo
>>> /etc/sudoers: syntax error near line 28 <<<
sudo: parse error in /etc/sudoers near line 28
sudo: no valid sudoers sources found, quitting

try using another access method like PolicyKit and fix the file up:

pkexec visudo -f /etc/sudoers.d/user

2.0 KiB Raw Blame History