Saturday, July 12, 2008 

How to: Using Sudo

What is sudo?

· Sudo is a command that allows users defined in the /etc/sudoers configuration file to have temporary root access to run certain privileged commands.

· The command you want to run must first begin with the word "sudo" followed by the regular command syntax.

· When running the command you will be prompted for your regular password before it is executed.You may run other privileged commands using sudo within a five minute period without being re-prompted for a password

· All commands run as sudo are logged in the log file /var/log/messages

Download and Install The sudo Package

Fortunately the package is installed by default by RedHat

The visudo Command

· "visudo" is the command used to edit the /etc/sudoers configuration file. It is not recommended that you use any other editor to modify your sudo parameters. "visudo" uses the same commands as the "vi" text editor.

· "visudo" is best run as user "root"

[root@aqua tmp]# visudo

The /etc/sudoers File

General Guidelines

o The /etc/sudoers file has the general format:

usernames/group target-servername = command

o Groups are the same as user groups and are differentiated from regular users by a % at the beginning

o The "#" at the beginning of a line signifies a comment line

o You can have multiple usernames per line separated by commas

o Multiple commands can be separated by commas too. Spaces are considered part of the command.

o The keyword "ALL" can mean all usernames, groups, commands and servers.

o If you run out of space on a line, you can end it with a "\" and continue on the next line.

o The NOPASSWD keyword provides access without you being prompted for your password

Simple sudoers Examples

o Users "paul" and "mary" have full access to all privileged commands

paul, mary ALL=(ALL) ALL

o Users with a groupid of "operator" has full access to all commands and won't be prompted for a password when doing so.


How To Use sudo

· In this example, user "paul" attempts to view the contents of the /etc/sudoers file

[paul@bigboy paul]$ more /etc/sudoers
/etc/sudoers: Permission denied

[paul@bigboy paul]$

· Paul tries again using sudo and his regular user password and is successful

[paul@bigboy paul]$ sudo more /etc/sudoers




[paul@bigboy paul]$

Using syslog To Track All sudo Commands

All sudo commands are logged in the log file /var/log/messages. Here is sample output from the above example.

[root@bigboy tmp]# grep sudo /var/log/messages
Nov 18 22:50:30 bigboy sudo(pam_unix)[26812]: authentication failure; logname=paul uid=0 euid=0 tty=pts/0 ruser= rhost= user=paul
Nov 18 22:51:25 bigboy sudo: paul : TTY=pts/0 ; PWD=/etc ; USER=root ; COMMAND=/bin/more sudoers
[root@bigboy tmp]#


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