關於sudoers中的admin group和sudo group

What
is the difference between the 'sudo' and 'admin' group?

I noticed that two groups are granted similar-looking permissions in /etc/sudoers:

# Members of the admin group may gain root privileges%admin ALL=(ALL) ALL# Allow members of group sudo to execute any command%sudo   ALL=(ALL:ALL) ALL

My user account with "Administer the system" privileges is in the admin group,
and there don't appear to be any users in the sudo group.
What are these two groups for?

Ubuntu 12.04 LTS and later

Administrators are added to the sudo group,
but the admin group
is supported for backward compatibility. From the release
notes:

Up until Ubuntu 11.10, administrator access using the sudo tool was granted via the admin Unix
group. In Ubuntu 12.04, administrator access will be granted via the sudo group.
This makes Ubuntu more consistent with the upstream implementation and Debian. For compatibility purposes, the admingroup
will continue to provide sudo/administrator access in 12.04.

It is not created when you do a fresh install, though it is still present if you upgraded from previous distributions. Either way, the admin group
appears in the /etc/sudoers file.

See implementation
details and the official
documentation.

Ubuntu 11.10 and earlier

By default the sudo group
is not used in Ubuntu:

• the user created during installation belongs to admin group,
  not sudo;
• no guide or manual I ever read advices to use the sudo group;
• no one feels the need to use the sudo group,
  because the admin group
  can do all one needs.

Conversely, on Debian the group enabled in /etc/sudoers is
the sudo group,
and there is no admingroup.
But the user created during installation is not put in that group, because Debian has the rootaccount
enabled. You should do it explicitly, if you want to.

Also, Fedora is similar to Debian,
having root enabled
and no default privileges for the user create during installation. But the administrative group configured in /etc/sudoers is
the more traditional groupwheel.

In conclusion, I think there is no use for sudo group
in Ubuntu, simply it is a Debian heritage.