What do the "ALL"s in the line " %admin ALL=(ALL) ALL " in Ubuntu's /etc/sudoers file stand for?

Solution 1:

There is a manual page for sudoers(5).

Basically:

• %admin – the group named "admin" (% prefix)
• ALL= – on all hosts (if you distribute the same sudoers file to many computers)
• (ALL) – as any target user
• ALL – can run any command

A more restricted example would be:

%mailadmin   snow,rain=(root) /usr/sbin/postfix, /usr/sbin/postsuper, /usr/bin/doveadm
nobody       ALL=(root) NOPASSWD: /usr/sbin/rndc reload

In this case, the group mailadmin is allowed to run mail server control tools as user root on hosts named "snow" and "rain". The user nobody is allowed to run rndc reload as root, on all hosts, without being asked for any password. (Normally sudo asks for the invoker's own password.)