snapd doesn't upgrade on bionic when a local installed snap mount is failing

[Marco Trevisan (Treviño)]

I installed a snap with 'try' some time ago when generating it, and then I never removed it.

However the actual snap doesn't exist anymore:
ls /var/lib/snapd/snaps/cool-retro-term* -l
lrwxrwxrwx 1 root root 36 feb 23 2017 /var/lib/snapd/snaps/cool-retro-term_x1.snap -> /tmp/cool-retro-term/packaging/prime
lrwxrwxrwx 1 root root 36 feb 23 2017 /var/lib/snapd/snaps/cool-retro-term_x2.snap -> /tmp/cool-retro-term/packaging/prime
lrwxrwxrwx 1 root root 36 feb 23 2017 /var/lib/snapd/snaps/cool-retro-term_x3.snap -> /tmp/cool-retro-term/packaging/prime

But now, snapd is failing when upgrading because it still tries to mount it.
I recognize this is a broken setup, but snapd installation should not hang because of this, but instead skip the mount.

Here's the log I've on apt:

Setting up snapd (2.32+18.04~pre6) ...
Starting snap-bucklespring-18.mount
Starting snap-bucklespring-23.mount
Starting snap-bucklespring-31.mount
Starting snap-cool\x2dretro\x2dterm-x1.mount
Job for snap-cool\x2dretro\x2dterm-x1.mount failed.
See "systemctl status "snap-cool\\x2dretro\\x2dterm-x1.mount"" and "journalctl -xe" for details.
dpkg: error processing package snapd (--configure):
 installed snapd package post-installation script subprocess returned error exit status 1
Processing triggers for libc-bin (2.27-0ubuntu2) ...
dpkg: dependency problems prevent configuration of ubuntu-core-launcher:
 ubuntu-core-launcher depends on snapd (= 2.32+18.04~pre6); however:
  Package snapd is not configured yet.

dpkg: error processing package ubuntu-core-launcher (--configure):
 dependency problems - leaving unconfigured
dpkg: dependency problems prevent configuration of ubuntu-snappy:No apport report written because the error message indicates its a followup error from a previous failure.
                   No apport report written because the error message indicates its a followup error from a previous failure.

 ubuntu-snappy depends on snapd; however:
  Package snapd is not configured yet.

dpkg: error processing package ubuntu-snappy (--configure):
 dependency problems - leaving unconfigured
dpkg: dependency problems prevent configuration of snapd-xdg-open:
 snapd-xdg-open depends on snapd (= 2.32+18.04~pre6); however:
  Package snapd is not configured yet.

dpkg: error processing package snapd-xdg-open (--configure):
 dependency problems - leaving unconfigured
dpkg: dependency problems prevent configuration of gnome-software-plugin-snap:
 gnome-software-plugin-snap depends on snapd; however:
  Package snapd is not configured yet.

dpkg: error processing package gnome-software-plugin-snap (--configure):
 dependency problems - leaving unconfigured
No apport report written because MaxReports is reached already
                                                              No apport report written because MaxReports is reached already
                                                                                                                            Errors were encountered while processing:
 snapd
 ubuntu-core-launcher
 ubuntu-snappy
 snapd-xdg-open
 gnome-software-plugin-snap
E: Sub-process /usr/bin/dpkg returned an error code (1)

[Marco Trevisan (Treviño) (3v1n0)]

of course removing the broken symlinks fixed the issue.

[Zygmunt Krynicki (zyga)]

There's some related work for better resiliency against unknown unknowns but it's not close to landing: https://github.com/snapcore/snapd/pull/7205