Just for the record, maybe there are more people out there that are late upgrading their servers from squeeze to wheezy...
When /etc/init.d/mysql start fails as described in this report, the command mysqld gives information on the command line what is going on. In my case, I had several errors, including the hint that I should run mysql_upgrade (which did not work, as it needs a running mysql server): 160307 21:49:22 [ERROR] Can't open the mysql.plugin table. Please run mysql_upgrade to create it. 160307 21:49:22 [ERROR] mysqld: unknown option '--skip-bdb' 160307 21:49:22 [ERROR] Aborting So in the end, in addition to using default-storage-engine=myisam I had to comment out the line #skip-bdb Johannes