package mysql-server-8.0 8.0.21-0ubuntu0.20.04.3 failed to install/upgrade: installed mysql-server-8.0 package pre-removal script subprocess returned error exit status 1

[D]

Trying to remove mysql and I got this.

ProblemType: Package
DistroRelease: Ubuntu 20.04
Package: mysql-server-8.0 8.0.21-0ubuntu0.20.04.3
ProcVersionSignature: Ubuntu 5.4.0-42.46-generic 5.4.44
Uname: Linux 5.4.0-42-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.4
Architecture: amd64
CasperMD5CheckResult: skip
Date: Wed Jul 29 03:03:07 2020
ErrorMessage: installed mysql-server-8.0 package pre-removal script subprocess returned error exit status 1
InstallationDate: Installed on 2020-07-26 (2 days ago)
InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
KernLog:

Logs.var.log.daemon.log:

MySQLConf.etc.mysql.conf.d.mysql.cnf: [mysql]
MySQLConf.etc.mysql.conf.d.mysqldump.cnf:
 [mysqldump]
 quick
 quote-names
 max_allowed_packet = 16M
MySQLVarLibDirListing: ['aria_log.00000001', 'aria_log_control', 'multi-master.info', 'performance_schema', 'ibdata1', 'ib_logfile0', 'ib_logfile1', 'ib_buffer_pool', 'debian-10.3.flag', 'mysql']
ProcCmdline: BOOT_IMAGE=/boot/vmlinuz-5.4.0-42-generic root=UUID=06a583c0-405d-40fc-9b81-57f15a2b0ffe ro quiet splash vt.handoff=7
Python3Details: /usr/bin/python3.8, Python 3.8.2, python3-minimal, 3.8.2-0ubuntu2
PythonDetails: /usr/bin/python2.7, Python 2.7.18rc1, python-is-python2, 2.7.17-4
RelatedPackageVersions:
 dpkg 1.19.7ubuntu3
 apt 2.0.2ubuntu0.1
SourcePackage: mysql-8.0
Title: package mysql-server-8.0 8.0.21-0ubuntu0.20.04.3 failed to install/upgrade: installed mysql-server-8.0 package pre-removal script subprocess returned error exit status 1
UpgradeStatus: No upgrade log present (probably fresh install)

[Paride Legovini (paride)]

Thanks for this bug report. The problem can be reproduced by running the following in a fresh Focal LXD container:

  apt update
  apt install mariadb-server
  apt remove mariadb-server
  apt install mysql-server

At this point mysql is in a very broken state. Its systemd units looks masked:

  # systemctl status mysql
  Unit mysql.service could not be found.

and this is why trying to remove it with:

  apt remove mysql-server-8.0

fails, as the uninstall process tried to `systemctl stop` the service. This is the error this bug report is about, but it's worse. If at this point we purge mariadb:

  apt purge mariadb-server-10.3

it will also delete the mysql user, which at this point should be "owned" by mysql - and possibly other things.

It seems that a Conflicts relationship between the two packages is not strong enough. Maybe Breaks could avoid this?

[Paride Legovini (paride)]

As noted by Robie @racb this is fundamentally a duplicate of:

https://bugs.launchpad.net/ubuntu/+source/mysql-5.7/+bug/1490071