Sudo

The command provides a simple and secure way to configure privilege escalation — i.e., letting normal users execute certain (or even all) commands as  or another user, either with or without giving a password.

To allow some users to perform certain administrative steps on a system without granting them total root access, using is the best option. Using allows control over who can do what. This guide offers a small introduction to this powerful tool.

This article is meant as a quick introduction. The package is a lot more powerful than what is described here. It has special features for editing files as a different user, running from within a script (so it can background, read the password from standard in instead of the keyboard, ...), etc.

Please read the and  manual pages for more information.

Logging activity
One additional advantage of is that it can log any attempt (successful or not) to run an application. This is very useful when tracking who made that one fatal mistake that took 10 hours to fix :)

Granting permissions
The package allows the system administrator to grant permission to other users to execute one or more applications they would normally have no right to. Unlike using the  bit on these applications  gives a more fine-grained control on who can execute a certain command and when.

With a clear list can be made of who can execute a certain application. If the setuid bit is set on an executable, any user would be able to run the application (or any user of a certain group, depending on the permissions used). With the user can (and probably should) be required to provide a password in order to execute the application.

The configuration is managed by the  file. This file should never be edited through or, or any other editor that is normally used. When altering the file, always use. This tool makes sure that no two system administrators are editing this file at the same time, preserves the permissions on the file, and performs some syntax checking to make sure no fatal mistakes in the file.

Basic syntax
The most difficult part of is the  syntax. The basic syntax is as follows:

This line tells that the user, identified by   and logged in on the system , can execute the command   (which can also be a comma-separated list of allowed commands).

A more real-life example might make this more clear: To allow the user to execute  when he is logged in on :

The user name can also be substituted with a group name, in which case the name is prefaced by a  sign. For instance, to allow any one in the group to execute :

To enable more than one command for a given user on a given machine, multiple commands can be listed on the same line. For instance, to allow to not only run  but also  and  as root:

The precise command line can also be specified (including parameters and arguments) not just the name of the executable. This is useful to restrict the use of a certain tool to a specified set of command options. The tool allows shell-style wildcards (AKA meta or glob characters) to be used in path names as well as command-line arguments in the sudoers file. Note that these are not regular expressions.

Here is an example of from the perspective of a first-time user of the tool who has been granted access to the full power of :

The password that requires is the user's own password. This is to make sure that no terminal that is accidentally left open to others is abused for malicious purposes.

Basic syntax with LDAP
The  and   USE flags are needed for the LDAP support.

When using sudo with LDAP, sudo will read configuration from LDAP Server as well. So two files will need to edited.

The following LDAP entry will need to added for sudo.

The configuration on the sudoer on LDAP are similar to files with some different. Please read more about sudo with LDAP on the link below.

Using aliases
In larger environments having to enter all users over and over again (or hosts, or commands) can be a daunting task. To ease the administration of aliases can defined. The format to declare aliases is quite simple:

One alias that always works, for any position, is the  alias (to make a good distinction between aliases and non-aliases it is recommended to use capital letters for aliases). The  alias is an alias to all possible settings.

A sample use of the  alias to allow any user to execute the  command if he is logged on locally is:

Another example is to allow the user to execute the  command as root, regardless of where he is logged in from:

More interesting is to define a set of users who can run software administrative applications (such as and ) on the system and a group of administrators who can change the password of any user, except root!

Non-root execution
It is also possible to have a user run an application as a different, non-root user. This can be very interesting when running applications as a different user (for instance for the web server) and want to allow certain users to perform administrative steps as that user (like killing zombie processes).

Inside list the user(s) in between   and   before the command listing:

For instance, to allow to run the  tool as the  or  user:

With this set, the user can run to select the user he wants to run the application as:

An alias can set for the user to run an application as using the  directive. Its use is identical to the other  directives we have seen before.

Passwords and default settings
By default, asks the user to identify himself using his own password. Once a password is entered, remembers it for 5 minutes, allowing the user to focus on his tasks and not repeatedly re-entering his password.

Of course, this behavior can be changed: set the  directive in  to change the default behavior for a user.

For instance, to change the default 5 minutes to 0 (never remember):

A setting of  would remember the password indefinitely (until the system reboots).

A different setting would be to require the password of the user that the command should be run as and not the users' personal password. This is accomplished using. In the following example we also set the number of retries (how many times the user can re-enter a password before fails) to   instead of the default 3:

Another interesting feature is to keep the  variable set so that graphical tools can be executed:

Dozens of default settings can changed using the  directive. Fire up the manual page and search for.

To allow a user to run a certain set of commands without providing any password whatsoever, start the commands with, like so:

Bash completion
Users that want bash completion with sudo need to run this once.

Zshell completion
Users that want zsh completion for sudo can set the following in and  respectively

With the above change, all commands in the, and  locations will be available to the shell for completion when the command is prefaced with 'sudo'.

Listing privileges
To list the current user's capabilities, run :

Any command in that does not require a password to be entered, a password will not be required to list the entries either. Otherwise sudo will ask for a password if it isn't remembered.

Prolonging password timeout
By default, if a user has entered their password to authenticate their self to, it is remembered for 5 minutes. If the user wants to prolong this period, he can run to reset the time stamp so that it will take another 5 minutes before  asks for the password again.

The inverse is to kill the time stamp using.