[Bug 1728055] Re: GDM3 hangs, if local home directory is not accessible

[Michal Kukuča]

I have finally found some time to look into this, and turns out, it's
not a problem anymore (with 18.04 at least). If I set the local user
back to normal (so it does appear in the greeter), GDM works normally
(it will display the user list, without any freezing). Of course, you
cannot log into the local user, because the home directory is simply not
there (the remote /home is mounted onto the local /home).

As a side note: when you do attempt a login into the local user (with
the correct credentials), you will not get any error message (apart from
the journal), which is not a very user-friendly solution - GDM just
restarts the greeter.

When I try to login using the terminal, the login will work (as it
always did - also with 17.10), but bash will complain, that it cannot
chdir into the home directory and access its stuff there.

So again: I posted this bug in October 2017, and I did not know then
where to properly post this and now (with Bionic) I can't reproduce the
problem. It probably was not a bug with autofs. What's relevant for me
now is the root_squash issue here: #1733101

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https://bugs.launchpad.net/bugs/1728055

Title:
  GDM3 hangs, if local home directory is not accessible

Status in autofs package in Ubuntu:
  Incomplete

Bug description:
  In Ubuntu 17.10 with GDM 3.26.1-3ubuntu3, the greeter will hang, if
  local /home directory is not accessible.

  Our setup:
  - Ubuntu Server (16.04) with DNS, LDAP, Kerberos 5 and NFS servers. The home directories are present on the server and made available via NFS with krb5 authentication. LDAP provides the user data for clients.
  - Ubuntu client (17.10), bound to the server, uses AutoFS to automount remote home directories under /home. This makes the otherwise present local user directories unaccessible.

  Expected behaviour: After system startup, the greeter should provide a way for users to log in.
  Actual behaviour: The system hangs before the greeter displays the user list (but it does display the top menu bar and Ubuntu logo at the bottom).

  Additional remarks:
  If the settings for local users under /var/lib/AccountsService/users contain SystemAccount=true, the greeter will work as expected (while not displaying local users). This is a workaround, that I'm using right now. BUT: if the network user will log in and invoke the authentication dialog for system-wide settings (e.g. if he will try to add a new printer, or change the system update settings), the system will hang before displaying the expected dialog window. Also if a local user will try to log in by entering his login name and password, the system will hang (it should either produce an error message, or log in without a home directory).

  AutoFS uses this line to mount the remote home directories under /home:
  * -fstype=nfs4,rw,intr,sec=krb5 FQDN:/home/&

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