[Bug 2129196] Re: mysql-server fails to install when an ext4 fs is mounted to /var/lib/mysql

[Lena Voytek]

Thanks for testing! I retried the jammy build and it should be ready to
test too now

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https://bugs.launchpad.net/bugs/2129196

Title:
  mysql-server fails to install when an ext4 fs is mounted to
  /var/lib/mysql

Status in mysql-8.0 package in Ubuntu:
  New
Status in mysql-8.4 package in Ubuntu:
  Fix Released
Status in mysql-8.0 source package in Jammy:
  Fix Committed
Status in mysql-8.0 source package in Noble:
  Fix Committed
Status in mysql-8.4 source package in Plucky:
  Fix Committed
Status in mysql-8.4 source package in Questing:
  Fix Committed
Status in mysql-8.4 source package in Resolute:
  Fix Released

Bug description:
  [ Impact ]

   * The postinst script for mysql-server checks whether the
  `/var/lib/mysql` directory is empty before setting up the database
  state. When `/var/lib/mysql` is an ext4 filesystem, the `lost+found`
  directory causes this check to fail and the database is not properly
  set up.

   * Mounting a separate volume to hold the mysql state is a common
  pattern, and ext4 is extremely prevalent so this is likely to be a
  common pain point. Although workarounds are straightforward, it makes
  for bad UX.

   * This can be remedied by ignoring the lost+found directory in the
  check.

  [ Test Plan ]

   To ensure bug is fixed:
   * Create an empty ext4 volume and mount it to /var/lib/mysql
   * Install mysql-server
   * Check whether the installation succeeds

   To check that data is preserved:
   * Uninstall and reinstall mysql-server
   * Ensure that the data in /var/lib/mysql is not overwritten

  [ Where problems could occur ]

   * In this case, the only change is to the postinst script, so problems should be related to install.
   * If the check being done were incorrect it could lead to loss of user data.
     - We keep the change to script to a minimum to reduce the risk of this
     - Test plan includes confirming that user data is not overwritten

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