After running apt-upgrade mariadb, it's possible that apt shows a fail in trying to start the server, but in fact the database is up and running, which then provokes apt to remain in a non finished state.

For example:

# apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
2 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n]
Setting up mariadb-server-10.1 (10.1.10+maria-1~trusty) ...
 * Stopping MariaDB database server mysqld
   ...done.
 * Starting MariaDB database server mysqld
   ...fail!
invoke-rc.d: initscript mysql, action "start" failed.
dpkg: error processing package mariadb-server-10.1 (--configure):
 subprocess installed post-installation script returned error exit status 1
dpkg: dependency problems prevent configuration of mariadb-server:
 mariadb-server depends on mariadb-server-10.1 (= 10.1.10+maria-1~trusty); however:
  Package mariadb-server-10.1 is not configured yet.
 
dpkg: error processing package mariadb-server (--configure):
 dependency problems - leaving unconfigured
No apport report written because the error message indicates its a followup error from a previous failure.
Errors were encountered while processing:
 mariadb-server-10.1
 mariadb-server
E: Sub-process /usr/bin/dpkg returned an error code (1)

This situation could occur if the timeout for the init script was too short. For example, see MDEV-9382, a situation where the timeout was 30 seconds, but the server was taking 48 seconds to start.

To overcome this, the timeout needs to be increased. This can be achieved as follows:

• On systems where systemd is not enabled/supported: The timeout can be increased by setting MYSQLD_STARTUP_TIMEOUT either directly in the script or via the command line. In MariaDB 10.1.13 and later versions, the init script also sources /etc/default/mariadb, so it can also be used to set MYSQLD_STARTUP_TIMEOUT to persistently change the startup timeout. The default timeout has been increased from 30s to 60s in MariaDB 10.1.13.

• On systems that support systemd: The startup timeout can be increased by setting TimeoutStartSec systemd option.