Subject: Re: bug#36508: GDM files have incorrect owner after temporarily removing service

From: Mark H Weaver <[email-masked]>
Date: Thu, 15 Apr 2021 14:58:16 -0400

Ludovic Courtès <[email-masked]> writes:

> Mark H Weaver <[email-masked]> skribis:
>
>> Here's one idea: when activating a system, *never* delete users or
>> groups if files still exist that are owned by those users/groups.
>> Checking all filesystems would likely be too expensive, but perhaps it
>> would be sufficient to check certain directories such as /var, /etc, and
>> possibly the top directory of /home.
>
> How would you determine which directories to look at though?  What if we
> miss an important one?

I have another idea:

Maintain historical mappings from user/group names to UIDs/GIDs, perhaps
in some file in /etc, where entries are added but *never* automatically
removed.  When allocating UIDs/GIDs, we would avoid any UIDs/GIDs in the
range of those mappings.

Then, provide a UID/GID garbage collector, to be explicitly run by users
if desired, which would scan all filesystems to find the set of UID/GIDs
currently referenced, and remove entries from the historical mappings
that are no longer needed.

What do you think?

      Mark