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Root > sudo

Sudo (sometimes considered as short for Super-user do) is a program designed to let system administrators allow some users to execute some commands as root (or another user). The basic philosophy is to give as few privileges as possible but still allow people to get their work done. Sudo is also an effective way to log who ran which command and when.

Why sudo?

Using sudo is better (safer) than opening a session as root for a number of reasons, including:

For the reasons above, switching to root using sudo -i (or sudo su) is usually deprecated because it cancels the above features.

Users and sudo

In order for a user to run sudo, the user must belong to group=sudo.

Verifying sudo membership

Once logged in as a user, you can verify whether or not the user belongs to group=sudo using either the id or groups commands. E.g., a user with id=foo should see output from


If sudo is not present in the output, the user does not belong to that group. Similarly, the more complex and variable output from command=id should look something like

Add existing user from commandline

To add an existing user with id=foo to group=sudo:

Alternatively, you can first get root (e.g., sudo su -) and then run the same commands without prefix=sudo:

After being added to a new group the user must log out and then log back in again for the new group to take effect. Groups are only assigned to users at login time. A most common source of confusion is that people add themselves to a new group but then do not log out and back in again and then have problems because the group is not assigned; be sure to verify group membership.

Creating users with sudo

You can also create new users with sudo membership:

Creating new user while installing OS

As of DebianSqueeze, if you give root an empty password during installation, sudo will be installed and the first user will be able to use it to gain root access (currently, the user will be added to the sudo group). The system will also configure gksu and aptitude to use sudo. You should still verify group membership after logging in as the installed user.

Creating new user from commandline

A user which already has sudo can create another user (example id=foo) with sudo group membership from the commandline:

(or first get root as in previous section). I am not aware of a way to accomplish this task with a single command (other than catenating the 2 commands above with ; which is not the same thing).

You should then login as the new user and verify group membership.

Configuration overview

Now, if you want to allow certain users to execute certain programs, here's a quick example (for more information, read the fine manual).

# /etc/sudoers
# This file MUST be edited with the 'visudo' command as root.
# See the man page for details on how to write a sudoers file.

Defaults        env_reset
Defaults        secure_path="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"

# Host alias specification
User_Alias      MYADMINS = jdoe

# User alias specification

# Cmnd alias specification
Cmnd_Alias      SHUTDOWN = /sbin/reboot, /sbin/poweroff
Cmnd_Alias      PKGMGMT = /usr/bin/dpkg, /usr/bin/apt-get, /usr/bin/aptitude

# User privilege specification

# Users listed above (MYADMINS) can run package managers and reboot the system.

# Allow members of group sudo to execute any command
%sudo   ALL=(ALL:ALL) ALL

#Default rule for root.
root    ALL=(ALL) ALL

#includedir /etc/sudoers.d

Problems and tips

PATH not set

A typical error using sudo to install a package might result in:

dpkg: warning: 'ldconfig' not found in PATH or not executable.
dpkg: warning: 'start-stop-daemon' not found in PATH or not executable.
dpkg: error: 2 expected programs not found in PATH or not executable.
Note: root's PATH should usually contain /usr/local/sbin, /usr/sbin and /sbin.

The packaged /etc/sudoers file contains this line:

Defaults secure_path="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"

Previous versions did not include that line. If you had a locally modified /etc/sudoers (most would) and then upgraded and kept your locally modified version then this required line is now missing. It no longer overrides your PATH when using sudo. This most likely results in PATH not being set properly and not including the system directories. The fix is to merge your local changes into the new package /etc/sudoers file. Or to put your local changes in the new /etc/sudoers.d/ location as a uniquely named file such as /etc/sudoers.d/local-sudoers. See 639841 for details.

Sorry, user jdoe is not allowed to execute ...

A typical session goes like this:

This message means what it says: the user you're running as isn't allowed to execute the given command on the given machine. One confusing possible reason for this is that the administrator has just added user jdoe to a privileged group - but you're still using the old login, which doesn't have that new group information, and therefore has no new sudo-ing rights. People in this situation are usually advised to log out completely and back in again, though you can sometimes get away with just performing a "re-login on the spot" with su - $USER

The include directive

The standard /etc/sudoers in Wheezy as of 1.8.2-1 ends with a line:

This makes it possible for other packages to provide snippets in /etc/sudoers.d/<packagename> which modify the configuration of sudo. It may look as if it needs to be edited to take out the leading numbersign (a.k.a. "hash" or "pound"), but no, the '#' is part of the directive!

sudoers is read-only

Yes, the file /etc/sudoers is intentionally set read-only, even for root!

The explanation usually offered is that it was set up this way to ensure that admins only ever edit it via the command visudo. However, this theory doesn't quite hold water. Being mode 0440 does nothing to impede sudo nano /etc/sudoers - most text editors will let you edit the file without complaining about the read-only bit. Besides, any time you do mangle /etc/sudoers, the fix may be as simple as su -c visudo, which is nothing compared to the kind of recovery procedure you'd have to go through if you broke something like /etc/inittab (mode 0644). So if there's a good reason for the unorthodox permissions, it's a mystery - contributions welcome.

Wrong HOME (and profile settings) behavior

If you are having problems when you sudo to your shell and your $HOME (and profile settings) doesn't work as expected because your new HOME is /root, you need to know that the default sudo configuration in Squeeze resets all environmental variables. To restore the old behavior of preserving the user's $HOME environment variable you can add this to your /etc/sudoers configuration file:

Defaults env_keep += HOME

Require root password

If you want to require the root password for use of sudo, rather than the user password, add the line:

Defaults   rootpw

For more information read the upstream changelog for version 1.7.4.

See also