July 28, 2009, 7:14 PM — If when setting up your sudoers file using the visudo command, you define a group of users and a group of commands, you can assign the command set to the use set without having to add a separate line for each user. Over the long haul, this might save you a lot of work. You could turn something that looks like this repetitive list of users and the commands they are allowed to run as root:
jesse ALL = /usr/bin/kill, /usr/sbin/halt, /usr/sbin/shutdown, /usr/sbin/reboot vail ALL = /usr/bin/kill, /usr/sbin/halt, /usr/sbin/shutdown, /usr/sbin/reboot rafael ALL = /usr/bin/kill, /usr/sbin/halt, /usr/sbin/shutdown, /usr/sbin/reboot
User_Alias OPS = jesse, vail, rafael Cmnd_Alias CONTROL = /usr/bin/kill, /usr/sbin/halt, /usr/sbin/shutdown, /usr/sbin/reboot OPS ALL = OPS
Of course, that isn't convincingly better unless you have a lot more lines in your file and a number of users who share the same set of responsibilities. For example, you might want to assign a certain set of commands to your system administrators, another to your developers and a third set to your technical support staff.
An out-of-the-box sudoers file will generally only contain some comments detailing where each type of alias is supposed to be defined and maybe one "root ALL=(ALL) ALL" command that allows root to run any command using sudo. The fleshed out, customized file may be hundreds of lines long with both privilege settings and explanations about what was intended. User aliases, as the above example illustrates, contain the keyword "User_Alias" as the first item on the line and are then followed by the alias name ("OPS" in the above example) and the list of commands. Notice that full paths are specified with each command. We don't want just any command by that name that might appear on the system to be run with the authority of root.
# User alias specification User_Alias SYSADMINS=shs,jdoe,allan User_Alias DEVELOPERS=chris,peter,martha,sally User_Alias WEBMASTERS=amy,sbob
Runas specifications determine the user or group that a command can be run as. For example, if we put the line "shs boson = (fred) /usr/bin/touch", then the user shs can issue the touch command as fred on boson. If we want to group runas users into an alias, we can do this:
Runas_Alias DB = oracle, postgres
The following line would then allow the user sbob to run any command on any system as oracle or postgres:
sbob ALL = (DB) ALL
You can group systems together in a Host-Alias in a similar manner.