4.4.3.2. The sudo Command

The sudo command offers another approach to giving users administrative access. When trusted users precede an administrative command with sudo, they are prompted for their own password. Then, once authenticated and assuming that the command is permitted, the administrative command is executed as if by the root user.

The basic format of the sudo command is as follows:

 sudo <command>

In the above example, <command> would be replaced by a command normally reserved for the root user, such as mount.

The sudo command allows for a high degree of flexibility. For instance, only users listed in the /etc/sudoers configuration file are allowed to use the sudo command and the command is executed in the user's shell, not a root shell. This means the root shell can be completely disabled, as shown in Section 4.4.1, “Allowing Root Access”.

The sudo command also provides a comprehensive audit trail. Each successful authentication is logged to the file /var/log/messages and the command issued along with the issuer's user name is logged to the file /var/log/secure.

Another advantage of the sudo command is that an administrator can allow different users access to specific commands based on their needs.

Administrators wanting to edit the sudo configuration file, /etc/sudoers, should use the visudo command.

To give someone full administrative privileges, type visudo and add a line similar to the following in the user privilege specification section:

 juan ALL=(ALL) ALL 

This example states that the user, juan, can use sudo from any host and execute any command.

The example below illustrates the granularity possible when configuring sudo:

 %users localhost=/sbin/shutdown -h now 

This example states that any user can issue the command /sbin/shutdown -h now as long as it is issued from the console.

The man page for sudoers has a detailed listing of options for this file.