[Bug 1566508] Re: autofs races with sssd on startup

[Maciej Puzio]

> Is it a daft question to ask why it works for them and not you ?

This is a very good question. My take on it is as follows.

There are several issues here, and the majority are related to startup
configuration. Speaking of Ubuntu 16.04, the problem is that Ubuntu
first switched from SysV startup to Upstart, and then (quite recently)
to systemd. Switch to Upstart was difficult and there were many problems
similar to this one, but before they were all ironed out, another switch
to systemd occurred. The result is a total mess. As an example, systemd
service unit is currently missing from autofs package, and so while for
sssd the switch was from Upstart to systemd, for autofs it was actually
Upstart -> SysV. And this is not the only issue.

Ubuntu 14.04, on the other hand, was released before the Upstart ->
systemd switch. Here the problem is that Upstart's event-driven model is
fundamentally flawed, and unable to express startup dependencies in a
general case (as opposed to installation-specific setup). This is the
reason why Upstart-related problems were not entirely fixed before the
switch to systemd: because they could not be fixed within Upstart
framework.

I have never used OpenSUSE, but I believe that it did not switch its
init system to Upstart, but rather directly from SysV to systemd. And it
did so much earlier than Ubuntu. Because of that it had a headstart and
much less mess to clean up, having to deal with only one switch. No
wonder then that its startup works better.

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https://bugs.launchpad.net/bugs/1566508

Title:
  autofs races with sssd on startup

Status in autofs package in Ubuntu:
  Confirmed
Status in sssd package in Ubuntu:
  Confirmed

Bug description:
  This report concerns a configuration where autofs and sssd are both
  installed, sssd is configured to provide automount maps, and
  nsswitch.conf directs autofs to use sssd. In such a configuration
  autofs often fails on boot complaining "no mounts in table". This is
  because autofs may be started before sssd, or after sssd is started
  but before its autofs support is ready. If this happens, one can
  restart autofs and it will work fine.

  This bug affects other users:
  * Bug 40189 "autofs needs to be restarted to pick up some shares" - a very old bug with invalid status, but see last comment #46, complaining about Ubuntu trusty: https://bugs.launchpad.net/ubuntu/+source/autofs/+bug/40189/comments/46
  * Link to SSSD-users mailing list, also complaining about Ubuntu trusty: https://lists.fedorahosted.org/pipermail/sssd-users/2015-July/003166.html

  $ lsb_release -rd
  Description:    Ubuntu 14.04.4 LTS
  Release:        14.04

  $ apt-cache policy autofs sssd
  autofs:
    Installed: 5.0.7-3ubuntu3.2
  sssd:
    Installed: 1.11.5-1ubuntu3

  $ uname -a
  Linux **** 3.13.0-83-generic #127-Ubuntu SMP Fri Mar 11 00:25:37 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

  Workaround:
  Edit /etc/init/autofs as shown in attached files (both full file and diff provided). Unfortunately, this modification will work only in this particular configuration, thus it is not a good candidate for a patch. 
  Explanation:
  We have to deal with two problems here:
  1. Autofs starts on runlevel [2345], and in effect its startup order in relation to sssd is random. We fix this by changing start stanza to "start on started sssd".
  2. Unfortunately this is not enough, because sssd emits started event too early, before its autofs support is ready. To work around this, we add a loop to pre-start script that waits for sssd to start listening on /var/lib/sss/pipes/autofs.

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