** Description changed:

- 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.
+ [Impact]
  
- Steps to reproduce:
+ 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
  
  [mysqld]
  super_read_only = ON
  read_only = ON
  EOF
  # service mysql restart
  # mysql -e "SELECT @@global.read_only, @@global.super_read_only;"
  +--------------------+--------------------------+
  | @@global.read_only | @@global.super_read_only |
  +--------------------+--------------------------+
- |                  1 |                        1 |
+ | 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
+  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:
-  mysql-server-5.7
+  mysql-server-5.7
  E: Sub-process /usr/bin/dpkg returned an error code (1)
  
  Step 3) should not cause a dpkg error.
  
- Additional information:
  
- # lsb_release -rd
- Description:  Ubuntu 18.04.4 LTS
- Release:      18.04
- # apt-cache policy mysql-server-5.7
- mysql-server-5.7:
-   Installed: 5.7.31-0ubuntu0.18.04.1
-   Candidate: 5.7.31-0ubuntu0.18.04.1
-   Version table:
-  *** 5.7.31-0ubuntu0.18.04.1 500
-         500 http://archive.ubuntu.com/ubuntu bionic-updates/main amd64 
Packages
-         500 http://security.ubuntu.com/ubuntu bionic-security/main amd64 
Packages
-         100 /var/lib/dpkg/status
-      5.7.21-1ubuntu1 500
-         500 http://archive.ubuntu.com/ubuntu bionic/main amd64 Packages
+ [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.

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https://bugs.launchpad.net/bugs/1889472

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

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