Comment 34 for bug 1273462

Both mysql-server-5.5 and mysql-server-5.6 packages (e.g. under Trusty Thar) provide a sysvinit script and an upstart job for mysql. The problem here is that the maintainer has a very strange approach:

1. The sysvinit script links are symply removed in the postinstall script using update-rc.d
2.The sysvinit script doesn't respects Debian policy section 9.11.1 which states that the sysvinit scripts should abort when an upstart job is provided (As I know, Ubuntu has choosen to follow Debian policy regarding cooexistence of upstart jobs and sysvinit scripts)

So yes, this situation can lead to several problems.

Anybody that run the mysql sysvinit script directly (/etc/init.d/mysql) instead of using service mysql <action> will have problems.

Also, if the upstart job is present, and if the sysvninit script is enabled (sysvinit script links created), the mysql socket will be missing on reboot.