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Re: System user names, uids, and gids


On Tue, Oct 23, 2018 at 01:40:57PM +0200, Steve Keller wrote:
> Debian uses some long (more than 8 chars) user and group names which I
> don't particularly like, e.g.
>     systemd-timesync
>     systemd-network
>     Debian-exim
>     messagebus
>     telnetd-ssl
> This is annoying with ps(1) which abbreviates these names.  For more
> than 20 years I have always limited user names to 8 chars on all my
> Unix and Unix-like systems.  Can I rename Debian's user names without
> problems or will they be re-created by apt the next time I install or
> upgrade an affected package?

In short - no. Such users are created by packages' postinst scripts, and
postinst scripts are called on each package upgrade.

> Also, I wonder why I have user names like Debian-exim in my
> /etc/passwd although I haven't installed exim.  It was part of the
> initial install but I have removed it afterwards.  Shouldn't the
> package management remove those user entries, too?

It can happen for some packages and it won't happen for the other.
Depends on whenever package's maintainer put an appropriate 'userdel
<foo>' in postrm script.

> May I remove it by hand?

As long as you don't have any package that's name starts with exim4
installed - sure. Should not break anything.

> Next, there are many names which are both, a user name and a group
> name.  However, I don't like that many of these don't have the same
> numeric uid and gid.  Are these IDs fixed in Debian or may I renumber
> them to my liking?

They only fix uids and gids if their number do not exceed 100, for
compatibility with other distributions/OSes.
These users, while seemingly 'system' ones, use random uids/gids.
Changing these gids/uids come with the usual caveat - don't forget to
change uids/gids for any filesystem objects (files, dirs, pipes, sockets
etc) that belonged to original gids/uids.