[EdLUG] Lubuntu 14.04 guest session login failure

Sun Jul 9 03:15:40 UTC 2017

Hi, a volunteer with higher sys admin skills came by the low income shelter
today and diagnosed a solution to the guest session login failure loop.
Here is what she wrote:

In case anyone was curious as to what happened with this, I finally
had some time to sit down on site this evening and do some debugging.

Some background as to how the guest logins work in Lubuntu: A
guest-XXXXX (random characters) user is created upon login, which is
used throughout the session. It is then deleted when the user logs
out.

After some red herrings in the auth logs (mostly PAM errors around KDE
and Gnome keyrings), I did some digging in the lightdm logs.
Eventually I noticed the UID of the guest account trying to be created
was the same every time a login attempt was made: 999. Odd. So I
looked in /etc/passwd and noticed that there were hundreds of
guest-XXXXX accounts. That's no good!

Turns out, at some point the /etc/subgid.lock file got stuck in an
existing state (wasn't deleted when the lock concluded), which meant
the command to delete the user was not completing successfully upon
logout. Users were piling up and never being deleted. Once the UIDs
hit 999 it was failing to create new guest users, so the login would
fail. A quick mv (rm didn't work) of the subgid.lock file and a script
to delete all the guest accounts got us going again.

I'm considering my options to get us out of this reoccurring issue in
the future. I'm thinking of just a cron job on each machine that
checks for a subgid.lock file sticking around for more than a couple
days and moving it out of the way, but I'll sleep on it. More clever
suggestions welcome ;)

Thanks for everyone who tried to help.  Any suggestions are welcome!

On Sat, Jul 8, 2017 at 5:03 PM, Edinburgh Linux Users Group <
edlug at lists.edlug.org.uk> wrote:

> Hi,
>
> I don't see how a guest could be causing this issue.  We are experiencing
> this guest session login failure loop on several machines at several
> difference low income shelters.  We are still stymied.  Someone suggested
> that removing appamor would work, but it didn't.
>
> On Tue, Apr 4, 2017 at 1:33 AM, Edinburgh Linux Users Group <
> edlug at lists.edlug.org.uk> wrote:
>
>> Hi Christian
>>
>> Are you saying that this problem occurs on one machine only? Could it be
>> that a "guest" has tried to make changes to the guest login and has broken
>> something?
>>
>> If these machines are all standard installs, would it be simpler to
>> reinstall instead of trying to solve a mysterious problem? If reinstalling
>> seems too much work (if there are a lot of customisations) I suggest making
>> an image backup (from one of the working machines) and restore (may be
>> handy to keep an image backup for this purpose anyway)
>>
>> Let us know how you get on.
>>
>> Regards
>> Geetam
>>
>> ---
>> I don't know
>> ...
>> I don't know what it is
>> ...
>> I don't know what it is that I don't know
>>
>> Isn't it beautiful
>>
>> On 4 April 2017 07:19:28 Edinburgh Linux Users Group <
>> edlug at lists.edlug.org.uk> wrote:
>>
>>> Hi,
>>>
>>> I am experiencing a very strange thing for which there are no ready
>>> answers by googling.  I am a volunteer for a non-profit which puts
>>> GNU-Linux computers in low income shelters.  They are stand-alone machines
>>> connected directly to the Internet via a hub on a dedicated ethernet cable.
>>>
>>> The shelters don't want the users to be able to store anything directly
>>> to the machine's hard drive.  To give them that functionality, we ask them
>>> to use the guest session, which wipes out all data by default when the
>>> session ends.
>>>
>>> Right now, however, we are experiencing a failure of logging into the
>>> guest session.  Normally, you just choose the guest session in the Lubuntu
>>> login screen, and hit enter, and it boots up a full guest session.  No
>>> password is required.
>>>
>>> Now, when I chose the guest session and hit enter, the system appears to
>>> head toward a normal login, but then quickly fails and returns to the login
>>> screen.
>>>
>>> The system's SU admin account is performing normally.  To get into the
>>> admin account, I just choose it in the login screen, enter the password,
>>> and the admin session boots up normally.
>>>
>>> This whole thing is very strange, and I have never seen anything like it
>>> before.  We are using 14.04 on 13 machines with identical or similar
>>> hardware and are not having any such problems.  This email is being written
>>> on one of those such machines, and the guest session works just fine.
>>>
>>> I ran updates on the malfunctioning machines, rebooted, no joy.
>>>
>>> Thanks very much in advance.
>>>
>>> --
>>> Christian Einfeldt
>>> _______________________________________________
>>> EdLUG mailing list
>>> EdLUG at lists.edlug.org.uk
>>> https://lists.edlug.org.uk/mailman/listinfo/edlug
>>>
>>
>> _______________________________________________
>> EdLUG mailing list
>> EdLUG at lists.edlug.org.uk
>> https://lists.edlug.org.uk/mailman/listinfo/edlug
>>
>>
>
>
> --
> Christian Einfeldt
>
> --
> EdLUG mailing list
> EdLUG at lists.edlug.org.uk
> https://lists.edlug.org.uk/mailman/listinfo/edlug
>

-- 
Christian Einfeldt
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