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Say you want to be able to easily see who's logged in to a system recently.

auth.log has this information, but it's very cluttered with crontab entries and you have to use sudo to read it.

Proposed solution:

  • Write a script to parse /var/log/auth.log looking for interesting things
  • Make root the owner of that script
  • Create a user who can't login
  • Add that user to the "adm" group, thus giving them read-only access to logfiles
  • Put the script in that user's crontab

What are the security risks of that solution? Adding someone to adm group seems risky, but if all they can do is run a script that's been checked to not do anything bad.

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up vote 0 down vote accepted

The solution should not pose a security risk by itself, unless output of the script is sent via mail or saved somewhere readable by other users.

The purpose of the adm-group is to allow users in that group to consult log files and /dev/console, used by eg. xconsole to display console messages.

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What's the risk of making this report visible to other users? We might want them to be able to see that information. – OJW Feb 22 '13 at 16:05
By "other users", I meant users who should not be able to read this information. Showing the authentication log (or parts thereof) might disclose information about the users or the system in question. – Cedric Feb 25 '13 at 14:17

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