Hi, I've work-arrounded the bug.
I had a timezone settings in my.cnf : [mysqld] ... default_time_zone="Europe/Paris" to define the time zone for my projects, and it seams this value breaks the launching of: MYSQL_BOOTSTRAP="/usr/sbin/mysqld --bootstrap --user=mysql --disable-log-bin --skip-grant-tables --default-storage-engine=myisam" from dpkg postinst script : the value is not recognized, and the direct launch of the server fails with 1 exit status, BUT, the systemctl start mysql still works. The workarround was to use: default_time_zone="+02:00" instead, and then the update goes on, without stopping the server. François GUÉRIN
