package snapd (not installed) failed to install/upgrade: installed snapd package post-removal script subprocess returned error exit status 1

[wilbur.harvey]

It failed to uninstall

ProblemType: Package
DistroRelease: Ubuntu 18.10
Package: snapd (not installed)
ProcVersionSignature: Ubuntu 4.18.0-11.12-generic 4.18.12
Uname: Linux 4.18.0-11-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.10-0ubuntu13.1
Architecture: amd64
Date: Thu Nov 29 08:59:40 2018
ErrorMessage: installed snapd package post-removal script subprocess returned error exit status 1
InstallationDate: Installed on 2018-09-04 (85 days ago)
InstallationMedia: Ubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
Python3Details: /usr/bin/python3.6, Python 3.6.7, python3-minimal, 3.6.7-1~18.10
PythonDetails: /usr/bin/python2.7, Python 2.7.15+, python-minimal, 2.7.15-3
RelatedPackageVersions:
 dpkg 1.19.0.5ubuntu5
 apt 1.7.0
SourcePackage: snapd
Title: package snapd (not installed) failed to install/upgrade: installed snapd package post-removal script subprocess returned error exit status 1
UpgradeStatus: Upgraded to cosmic on 2018-11-01 (28 days ago)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Maciej Borzecki (maciek-borzecki)]

This piece of terminal output is interesting:

Waiting until unit snap-lxd-9664.mount is stopped [attempt 19]
Waiting until unit snap-lxd-9664.mount is stopped [attempt 20]
Removing snap lxd and revision 9664
rm: cannot remove '/var/snap/lxd/common/ns/shmounts': Device or resource busy
dpkg: error processing package snapd (--purge):
 installed snapd package post-removal script subprocess returned error exit status 1

So even though the lxd daemon was stopped at the beginning, it did not clean up properly (or was there a container still running?).

[Tom Reynolds (tomreyn)]

Potential dupe of bug 1788702?

[Anony Moose (foobidoo)]

For me uninstalling failed because of the ZFS mount on /var/snap. After I unmounted /var/snap with sudo umount /var/snap (which was empty)