[Bug 1594658] Re: diskless setup with nfs mounted home hangs on shutdown/reboot

[Ralf Menzel]

I have the same (or a similar) problem on a system with a wired ethernet
connection.

Using the debug-shell I found that the shutdown was hanging on a call of

  /bin/sh /sbin/resolvconf -d enp0s25.inet

Here enp0s25 is the ethernet interface. It has a static configuration
that contains "dns-nameservers" and "dns-search" lines.

Adding some diagnostic output to /sbin/resolvconf I found that it seems
to hang in the case statement that spans lines 31 to 37. After some
trial and error I change the pattern in line 36 from

  ~*

to

  '~'*

With this change shutdown now proceeds smoothly.

I'm not an expert shell programmer, so I don't know why the change has
this effect. Looks almost like some obscure dash bug to me.

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https://bugs.launchpad.net/bugs/1594658

Title:
  diskless setup with nfs mounted home hangs on shutdown/reboot

Status in nfs-utils package in Ubuntu:
  Confirmed
Status in systemd package in Ubuntu:
  Confirmed

Bug description:
  Ubuntu 16.04 fresh install hangs when shutting down.
  The system is diskless PXE-booted with a couple of nfs mounted directories including homedir.

  As I have no persistent storage whatsoever, I don't have any logs, but
  in debug-shell, running journalctl -f I can see that it hangs at

  [   *] (1 of 2) A stop job running for Raise Network Interfaces (10s / 1min 30s)Jun 20 20:23:05 $hostname kernel: nfs: server $nfs-ip-address not responding, still trying
  Jun 20 20:23:05 $hostname kernel: nfs: server $nfs-ip-address not responding, still trying
  Jun 20 20:23:14 $hostname kernel: nfs: server $nfs-ip-address not responding, still trying
  Jun 20 20:24:08 $hostname kernel: nfs: server $nfs-ip-address not responding, still trying

  Second job in "(1 of 2)" is thermald, turning it off does not fix the problem.
  Also, this counter "(10s / 1min 30s)" stops visually updating.

  server $nfs-ip-address is not responding, because, all network
  interfaces are already down at this point.

  I am not exactly sure why this happens. Looks like there is a wrong
  ordering of shutdown of systemd services, which bring down interfaces
  before something nfs-related, but I am not sure if that's the reason
  of hanging.

  
  Workaround that fixes the problem:
  In /lib/systemd/system/networking.service
  comment following line:
  ExecStop=/sbin/ifdown -a --read-environment

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