Comment 21 for bug 1638125

10.0.28-0ubuntu0.16.10.1 was applied last night as an unattended update to my server and wiped out /var/lib/mysql...

Log started: 2016-12-08 03:37:45
Preconfiguring packages ...
(Reading database ... ^M(Reading database ... 5%^M(Reading database ... 10%^M(Reading database ... 15%^M(Reading database ... 20%^M(Reading database ... 25%^M(Reading database ... 30%^M(Reading database ... 35%^M(Reading database ... 40%^M(Reading database ... 45%^M(Reading database ... 50%^M(Reading database ... 55%^M(Reading database ... 60%^M(Reading database ... 65%^M(Reading database ... 70%^M(Reading database ... 75%^M(Reading database ... 80%^M(Reading database ... 85%^M(Reading database ... 90%^M(Reading database ... 95%^M(Reading database ... 100%^M(Reading database ... 172311 files and directories currently installed.)
Preparing to unpack .../mariadb-common_10.0.28-0ubuntu0.16.04.1_all.deb ...
Unpacking mariadb-common (10.0.28-0ubuntu0.16.04.1) over (10.0.27-0ubuntu0.16.04.1) ...
Preparing to unpack .../mariadb-client-core-10.0_10.0.28-0ubuntu0.16.04.1_amd64.deb ...
Unpacking mariadb-client-core-10.0 (10.0.28-0ubuntu0.16.04.1) over (10.0.27-0ubuntu0.16.04.1) ...
Processing triggers for man-db (2.7.5-1) ...
Setting up mariadb-common (10.0.28-0ubuntu0.16.04.1) ...
(Reading database ... ^M(Reading database ... 5%^M(Reading database ... 10%^M(Reading database ... 15%^M(Reading database ... 20%^M(Reading database ... 25%^M(Reading database ... 30%^M(Reading database ... 35%^M(Reading database ... 40%^M(Reading database ... 45%^M(Reading database ... 50%^M(Reading database ... 55%^M(Reading database ... 60%^M(Reading database ... 65%^M(Reading database ... 70%^M(Reading database ... 75%^M(Reading database ... 80%^M(Reading database ... 85%^M(Reading database ... 90%^M(Reading database ... 95%^M(Reading database ... 100%^M(Reading database ... 172311 files and directories currently installed.)
Preparing to unpack .../mariadb-server-10.0_10.0.28-0ubuntu0.16.04.1_amd64.deb ...
/var/lib/mysql: found previous version 10.0
Unpacking mariadb-server-10.0 (10.0.28-0ubuntu0.16.04.1) over (10.0.27-0ubuntu0.16.04.1) ...
Preparing to unpack .../mariadb-client-10.0_10.0.28-0ubuntu0.16.04.1_amd64.deb ...
Unpacking mariadb-client-10.0 (10.0.28-0ubuntu0.16.04.1) over (10.0.27-0ubuntu0.16.04.1) ...
Preparing to unpack .../mariadb-server-core-10.0_10.0.28-0ubuntu0.16.04.1_amd64.deb ...
Unpacking mariadb-server-core-10.0 (10.0.28-0ubuntu0.16.04.1) over (10.0.27-0ubuntu0.16.04.1) ...
Preparing to unpack .../mariadb-server_10.0.28-0ubuntu0.16.04.1_all.deb ...
Unpacking mariadb-server (10.0.28-0ubuntu0.16.04.1) over (10.0.27-0ubuntu0.16.04.1) ...
Processing triggers for systemd (229-4ubuntu12) ...
Processing triggers for ureadahead (0.100.0-19) ...
Processing triggers for man-db (2.7.5-1) ...
Setting up mariadb-client-core-10.0 (10.0.28-0ubuntu0.16.04.1) ...
Setting up mariadb-client-10.0 (10.0.28-0ubuntu0.16.04.1) ...
Setting up mariadb-server-core-10.0 (10.0.28-0ubuntu0.16.04.1) ...
Setting up mariadb-server-10.0 (10.0.28-0ubuntu0.16.04.1) ...
this is very strange! see /tmp/mysql-symlink-restore-forbvv/README...
Setting up mariadb-server (10.0.28-0ubuntu0.16.04.1) ...
Log ended: 2016-12-08 03:38:56

Left this lovely note:

/tmp/mysql-symlink-restore-forbvv/README:

If you're reading this, it's most likely because you had replaced /var/lib/mysql
with a symlink, then upgraded to a new version of mysql, and then dpkg
removed your symlink (see #182747 and others). The mysql packages noticed
that this happened, and as a workaround have restored it. However, because
/var/lib/mysql seems to have been re-created in the meantime, and because
e don't want to rm -rf something we don't know as much about, we are going
to leave this unexpected directory here. If your database looks normal,
and this is not a symlink to your database, you should be able to blow
this all away.