package mysql-server-5.5 5.5.40-0ubuntu0.14.04.1 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1

[Trev]

Ubuntu reported incomplete updates and recommended oartial upgrade. Went ahead with download of 100mb all went well except mysql 5.5 which was reported to me as a bug in the update.

ProblemType: Package
DistroRelease: Ubuntu 14.04
Package: mysql-server-5.5 5.5.40-0ubuntu0.14.04.1
ProcVersionSignature: Ubuntu 3.13.0-37.64-generic 3.13.11.7
Uname: Linux 3.13.0-37-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.5
Architecture: amd64
Date: Fri Oct 17 11:08:06 2014
DuplicateSignature: package:mysql-server-5.5:5.5.40-0ubuntu0.14.04.1:subprocess installed post-installation script returned error exit status 1
ErrorMessage: subprocess installed post-installation script returned error exit status 1
InstallationDate: Installed on 2012-12-22 (663 days ago)
InstallationMedia: Ubuntu 12.10 "Quantal Quetzal" - Release amd64 (20121017.5)
Logs.var.log.daemon.log:

MySQLConf.etc.mysql.conf.d..keepme:
MySQLConf.etc.mysql.conf.d.mysqld.safe.syslog.cnf:
 [mysqld_safe]
 syslog
MySQLVarLibDirListing: ['ib_logfile0', 'ib_logfile1', 'debian-5.5.flag', 'mysql_upgrade_info', 'mysql', 'ibdata1', 'performance_schema']
ProcCmdline: BOOT_IMAGE=/boot/vmlinuz-3.13.0-37-generic root=UUID=655697f5-6807-4a38-962c-57843634b535 ro
SourcePackage: mysql-5.5
Title: package mysql-server-5.5 5.5.40-0ubuntu0.14.04.1 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1
UpgradeStatus: Upgraded to trusty on 2014-04-19 (180 days ago)

[Launchpad Janitor (janitor)]

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

[Yuv (yuv)]

I encountered the same problem and solved it. I have tried a number of things, so I am not 100% sure which one it is that solved it. If I were to do it all from scratch again, this is my suggestion for troubleshooting the problem:

1. look at /var/log/mysql/error.log for lines with the [ERROR] tag. In my case, the one preventing mysqld from starting (and thus breaking the upgrade which expected a running mysqld) was

  141109 10:48:23 [ERROR] /usr/sbin/mysqld: unknown variable 'default-character-set=utf8'

2. search for the meaning of the error message. In my case, I found <http://dev.mysql.com/doc/refman/5.5/en/server-options.html#option_mysqld_default-character-set>

3. edit /etc/mysql/my.ini to remove the source of the error. In my case, I changed the old charset and collation default options to

  # deprecated:
  # default-character-set=utf8
  # default-collation=utf8_unicode_ci
  # the newer options:
  character-set-server=utf8
  collation-server=utf8_unicode_ci

4. try again to start mysqld / run the upgrade and repeat until there are no new errors in the error log and mysqld is started after the upgrade.

  sudo apt-get upgrade
  sudo service mysql start

5. if necessary, try reinstalling (I did this, not sure it contributed to the solution, but just in case):
  sudo apt-get remove mysql-client* mysql-server*
  sudo apt-get install mysql-server

[Yuv (yuv)]

Potential solutions to the bug report:
(1) The lazy solution: this report will be marked as invalid, because the problem is not in the package but in the user's configuration file
(2) The smart solution: a parser to check the user's configuration file and issue warnings for deprecated configuration options
(3) The mid-way solution: catch the exit status code after starting mysqld and if it fails to start suggest to the user to investigate their configuration file
(4) An alternative solution: catch the exit status code after starting mysqld and if it fails to start, put forward the option to the user to backup the old configuration file and install a fresh one