Ubuntu
mysql-5.7 package

  1. Bug #1567612
  2. Comment #9

Comment 9 for bug 1567612

Revision history for this message
Lars Tangvald (lars-tangvald) wrote : Re: package mysql-server-5.7 not installed failed to install/upgrade: subprocess installed post-installation script returned error exit status 11

The values being missing would also explain why it said your debian-sys-maint has an empty password;
Postinst will try to log in as debian-sys-maint first. If that fails it will try to read the password from debian.cnf and set that as the user's password, then run mysql_upgrade.
I'm thinking that maybe if that login check fails we should simply overwrite the debian.cnf file with a new one.