Unable to purge snapd on the freshly installed system

[Norbert]

Steps to reproduce:
1. Have Ubuntu 24.04 LTS installed from 20240323 ISO
2. Install Konqueror browser to make it fallback web-browser by `sudo apt-get install konqueror --no-install-recommends`
3. Try to purge Snapd from the system by `sudo apt autopurge snapd`

Expected results:
* Snapd purged, /snap and /var/snap directories are removed

Actual results:
* got many errors in the terminal (see below), /snap and /var/snap directories are not removed:

```
$ sudo apt autopurge snapd
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
The following packages will be REMOVED:
  snapd*
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
After this operation, 0 B of additional disk space will be used.
N: Ignoring file 'ubuntu.sources.curtin.old' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension
Do you want to continue? [Y/n]
(Reading database ... 173821 files and directories currently installed.)
Purging configuration files for snapd (2.60.4+23.10) ...
Stopping snap-firefox-4033.mount
Stopping unit snap-firefox-4033.mount
Waiting until unit snap-firefox-4033.mount is stopped [attempt 1]
snap-firefox-4033.mount is stopped.
Removing snap firefox and revision 4033
rm: cannot remove '/var/snap/firefox/common/host-hunspell/en_AU.aff': Read-only file system
rm: cannot remove '/var/snap/firefox/common/host-hunspell/fr.dic': Read-only file system
rm: cannot remove '/var/snap/firefox/common/host-hunspell/fr_FR.aff': Read-only file system
rm: cannot remove '/var/snap/firefox/common/host-hunspell/fr_LU.aff': Read-only file system
rm: cannot remove '/var/snap/firefox/common/host-hunspell/fr_LU.dic': Read-only file system
rm: cannot remove '/var/snap/firefox/common/host-hunspell/en_US.dic': Read-only file system
rm: cannot remove '/var/snap/firefox/common/host-hunspell/fr_CA.dic': Read-only file system
rm: cannot remove '/var/snap/firefox/common/host-hunspell/en_ZA.dic': Read-only file system
rm: cannot remove '/var/snap/firefox/common/host-hunspell/fr.aff': Read-only file system
rm: cannot remove '/var/snap/firefox/common/host-hunspell/en_GB.aff': Read-only file system
rm: cannot remove '/var/snap/firefox/common/host-hunspell/fr_BE.aff': Read-only file system
rm: cannot remove '/var/snap/firefox/common/host-hunspell/fr_CH.dic': Read-only file system
rm: cannot remove '/var/snap/firefox/common/host-hunspell/fr_BE.dic': Read-only file system
rm: cannot remove '/var/snap/firefox/common/host-hunspell/en_CA.dic': Read-only file system
rm: cannot remove '/var/snap/firefox/common/host-hunspell/fr_CH.aff': Read-only file system
rm: cannot remove '/var/snap/firefox/common/host-hunspell/fr_CA.aff': Read-only file system
rm: cannot remove '/var/snap/firefox/common/host-hunspell/en_ZA.aff': Read-only file system
rm: cannot remove '/var/snap/firefox/common/host-hunspell/fr_FR.dic': Read-only file system
rm: cannot remove '/var/snap/firefox/common/host-hunspell/fr_MC.dic': Read-only file system
rm: cannot remove '/var/snap/firefox/common/host-hunspell/fr_MC.aff': Read-only file system
rm: cannot remove '/var/snap/firefox/common/host-hunspell/en_CA.aff': Read-only file system
rm: cannot remove '/var/snap/firefox/common/host-hunspell/en_GB.dic': Read-only file system
rm: cannot remove '/var/snap/firefox/common/host-hunspell/en_US.aff': Read-only file system
rm: cannot remove '/var/snap/firefox/common/host-hunspell/en_AU.dic': Read-only file system
dpkg: error processing package snapd (--purge):
 installed snapd package post-removal script subprocess returned error exit status 1
Errors were encountered while processing:
 snapd
E: Sub-process /usr/bin/dpkg returned an error code (1)

$ sudo du -sh /snap/
72K /snap/

$ sudo du -sh /var/snap/
12M /var/snap/
```

ProblemType: Package
DistroRelease: Ubuntu 24.04
Package: snapd (not installed)
ProcVersionSignature: Ubuntu 6.8.0-11.11-generic 6.8.0-rc4
Uname: Linux 6.8.0-11-generic x86_64
ApportVersion: 2.28.0-0ubuntu1
AptOrdering:
 snapd:amd64: Purge
 NULL: ConfigurePending
 NULL: PurgePending
 NULL: ConfigurePending
Architecture: amd64
CasperMD5CheckResult: pass
Date: Sat Mar 23 17:43:57 2024
ErrorMessage: installed snapd package post-removal script subprocess returned error exit status 1
InstallationDate: Installed on 2024-03-23 (0 days ago)
InstallationMedia: Ubuntu 24.04 LTS "Noble Numbat" - Daily amd64 (20240323)
Python3Details: /usr/bin/python3.12, Python 3.12.2, python3-minimal, 3.12.1-0ubuntu2
PythonDetails: N/A
RelatedPackageVersions:
 dpkg 1.22.4ubuntu5
 apt 2.7.12
SourcePackage: snapd
Title: package snapd (not installed) failed to install/upgrade: installed snapd package post-removal script subprocess returned error exit status 1
UpgradeStatus: No upgrade log present (probably fresh install)

[Amin Bandali (bandali)]

Hello,

This appears to be due to the Firefox snap's use of the mount-control interface for accessing system hunspell dictionaries. There is work in progress for moving away from mount-control and using a simpler and cleaner approach of using system-files for that instead, which should also alleviate this.

However, ideally snapd should handle a case like this properly, so thanks for marking this bug as affecting snapd as well.

[Launchpad Janitor (janitor)]

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