[Bug 1889472] Re: mysql-server-5.7 postinst fails when in read-only mode

Simon Déziel 1889472 at bugs.launchpad.net
Mon Apr 12 11:35:15 UTC 2021

Thanks you. Batching this with the next security update seems like the 
best approach to me.

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  mysql-server-5.7 postinst fails when in read-only mode

Status in mysql-5.7 source package in Xenial:
  Won't Fix
Status in mysql-5.7 source package in Bionic:

Bug description:

  Updates of the mysql-server-5.7 package fail to install (error during postinst) if operating in (super) read-only mode.
  A read-only replica is common in redundant/HA setups.

  [Test Case]

  1) Setup a container (bionic or xenial would do)
  $ lxc launch images:ubuntu/bionic sql1
  $ lxc shell sql1
  # apt-get update && apt-get install -y --no-install-recommends mysql-server

  2) Configure read-only mode
  # cat << EOF >> /etc/mysql/my.cnf

  super_read_only = ON
  read_only = ON
  # service mysql restart
  # mysql -e "SELECT @@global.read_only, @@global.super_read_only;"
  | @@global.read_only | @@global.super_read_only |
  | 1 | 1 |

  3) Trigger the postinst code
  # apt-get install --reinstall mysql-server-5.7
  Reading package lists... Done
  Building dependency tree
  Reading state information... Done
  0 upgraded, 0 newly installed, 1 reinstalled, 0 to remove and 0 not upgraded.
  Need to get 0 B/2,931 kB of archives.
  After this operation, 0 B of additional disk space will be used.
  Preconfiguring packages ...
  (Reading database ... 16169 files and directories currently installed.)
  Preparing to unpack .../mysql-server-5.7_5.7.31-0ubuntu0.18.04.1_amd64.deb ...
  Unpacking mysql-server-5.7 (5.7.31-0ubuntu0.18.04.1) over (5.7.31-0ubuntu0.18.04.1) ...
  Setting up mysql-server-5.7 (5.7.31-0ubuntu0.18.04.1) ...
  Checking if update is needed.
  Checking server version.
  Running queries to upgrade MySQL server.
  mysql_upgrade: [ERROR] 1290: The MySQL server is running with the --super-read-only option so it cannot execute this statement
  mysql_upgrade failed with exit status 5
  dpkg: error processing package mysql-server-5.7 (--configure):
   installed mysql-server-5.7 package post-installation script subprocess returned error exit status 1
  Processing triggers for systemd (237-3ubuntu10.41) ...
  Errors were encountered while processing:
  E: Sub-process /usr/bin/dpkg returned an error code (1)

  Step 3) should not cause a dpkg error.

  [Regression Potential]

  This patch runs a MySQL query to check if the service is in (super) read-only mode before calling mysql_upgrade. The SQL query might
  fail thus preventing the proper detection of the read-only mode. The patch assumes read-write mode by default so that it would still
  call mysql_upgrade. Fortunately, mysql_upgrade is known to safely error out when in read-only as this is what the bug is about.

  Another possibility is to wrongly detect read-only mode which would skip running mysql_upgrade when it should have been. To mitigate
  this, the patch informs the user ("mysql_upgrade skipped due to (super) read-only mode") who could then run mysql_upgrade manually.

  [Other Info]

  If and when the patch lands in -proposed, I will update the test
  instructions to indicate that -proposed needs to be enabled and mysql-
  server-* should be upgraded instead of --reinstall'ed.

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