<seb128> what should packages handle deluser calls in postrm/purge that fail 
because the user is logged in
 like lightdm when users try to remove the package from a system when the login 
manager is in use
<pitti> seb128: TBH I think nothing should ever call deluser automatically
 if a postrm is trying to, then at least with || true
<seb128> pitti, so purging lightdm should just let a lightdm user around?
<pitti> but the possibility of reusing a previously removed uid for a new 
account is a security issue
 seb128: yeah, I think that's the lesser evil
<seb128> pitti, so you would just drop the deluser call?
 rather than adding || true?
<pitti> lightdm is prone to leaking processes and leftover sessions 
unfortunately
 seb128: no strong opinion between || true and drop, but I'd prefer dropping 
it, yes
<seb128> pitti, thanks
<seb128> robert_ancell, ^
<pitti> seb128: so the problem is:
<pitti> 1. you uninstall package foo with sysuser foo, removing the sysuser foo 
with uid 123
 2. you install a package bar, adding sysuser bar with uid 123 (reusing)
 3. now bar's daemons "take over" any running processes of foo, and can meddle 
with its leftover files, etc.
<robert_ancell> pitti, fair point
<seb128> right
<pitti> in some cases (when foo doesn't write any files, or makes sure to kill 
its processes), deluser is a nice cleanup, but this should be ascertained before
 and lightdm in particular writes lots of files and leaks lots of sessions and 
processes
 at least while it's running I always have a lightdm session around; not sure 
whether that's still true after stopping lightdm

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https://bugs.launchpad.net/bugs/924224

Title:
  LightDM package fails to remove if lightdm user is in use

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