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I'm trying to make sense of the sudo documentation on the Debian Wiki. On it, it uses the two examples below. However I don't understand the difference between them. Why has the group sudo got (ALL:ALL) as compared to the (ALL) option for root? What does each part of the command do.

# Allow members of group sudo to execute any command
%sudo   ALL=(ALL:ALL) ALL

#Default rule for root.
root    ALL=(ALL) ALL

2 Answers 2

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Eplanation for %sudo ALL=(ALL:ALL) ALL:-

  • %sudo - the group (named sudo) allowed to use sudo.

  • 1st ALL means to allow sudo from any terminal, or from any host (on any machine)

  • (ALL:ALL) indicates command can be run as (User:Group)
  • Last All means all commands can be executed

Explanation for root ALL=(ALL) ALL

  • root - the user (root) allowed to do everything on any machine as any user

Explanation for (ALL:ALL): (Run as (User:Group))

  • 1st "ALL" indicates that the user (in case of root) or group members (in case of %admin) can run commands as all users

  • 2nd "ALL" indicates that user (i.e root) or group members (i.e. of %admin) can run commands as all groups.

If only (ALL) is used then it doesn't allow to run as another group whereas (ALL:ALL) says Run as All users and All groups.

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  • So I assume that there is no point in actually having (ALL:ALL) as it does the same as putting (ALL)?
    – john smith
    Jun 18, 2015 at 11:11
  • @johnsmith as my answer shows, ALL:ALL is not the same as just ALL.
    – muru
    Jun 18, 2015 at 11:14
  • @johnsmith have you read last line?
    – Pandya
    Jun 18, 2015 at 11:18
  • I find your answer confusing. I thought that the root settings are nothing to do with sudo. So I'm not sure why you refer to sudo in your explination of the root command.
    – john smith
    Jun 18, 2015 at 11:20
  • Unless the ALL command is also used as an alias to do something with sudo, which would be super confusing, but hilarious
    – john smith
    Jun 18, 2015 at 11:21
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The difference between ALL:ALL and ALL in RunAs is the combinations of user and group that can be used. For example:

# sudo -u muru -g git id
Sorry, user root is not allowed to execute '/usr/bin/id' as muru:git on muru-laptop.
# sudo -u muru -g muru id
uid=1000(muru) gid=1000(muru) groups=1000(muru),10(wheel),21(locate),102(polkitd),190(systemd-journal)
$ sudo -u muru -g git id
uid=1000(muru) gid=997(git) groups=997(git),10(wheel),21(locate),102(polkitd),190(systemd-journal),1000(muru)
$ id    
uid=1000(muru) gid=1000(muru) groups=1000(muru),10(wheel),21(locate),102(polkitd),190(systemd-journal)

The first two commands were run as root, the third and fourth under my normal user who has (ALL:ALL).

With only ALL, -g can only be used to specify the primary group of the user - which is no better than not specifying -g at all. ALL:ALL can be used to give any combination of valid users and groups.

I don't know why this (artificial) restriction is in place.

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  • 1
    Oh man. I am a new linux user, this is way over my head.
    – john smith
    Jun 18, 2015 at 11:10
  • @johnsmith <shrug> I doubt you'd have to actually use a combination this way. Most cases require just the user, or nothing at all.
    – muru
    Jun 18, 2015 at 11:13

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