Comment 1 for bug 1768356

Fixed with "fuser -vik /var/cache/debconf/config.dat" but apparently some seconds later it was already unlocked.

# apt --fix-broken install
Reading package lists... Done
Building dependency tree
Reading state information... Done
Correcting dependencies... Done
The following packages were automatically installed and are no longer required:
  ca-certificates-mono cli-common dbconfig-common dbconfig-mysql default-mysql-client default-mysql-server libapache2-mod-php libapache2-mod-php7.2 libdbi1 libexpat1-dev libgdiplus libglib2.0-cil libgsl23
  libgslcblas0 libgtk2.0-cil libjs-c3 libjs-chartjs libjs-d3 libjs-jquery-colorpicker libjs-jquery-cookie libjs-jquery-hotkeys libjs-jquery-jstree libjs-jquery-metadata libjs-jquery-tablesorter
  libjs-jquery-timepicker libjs-jquery-ui libjs-jquery-ui-theme-smoothness libjs-jquery-ui-theme-south-street libjs-jquery-ui-theme-ui-darkness libjs-jquery-ui-touch-punch libmono-addins-gui0.2-cil
  libmono-addins0.2-cil libmono-cairo4.0-cil libmono-corlib4.5-cil libmono-i18n-west4.0-cil libmono-i18n4.0-cil libmono-posix4.0-cil libmono-security4.0-cil libmono-sharpzip4.84-cil
  libmono-system-configuration4.0-cil libmono-system-core4.0-cil libmono-system-drawing4.0-cil libmono-system-security4.0-cil libmono-system-xml4.0-cil libmono-system4.0-cil libopencolorio1v5
  libphp-phpmailer libpython3-dev libpython3.6-dev librrd8 libtinyxml2.6.2v5 libyaml-cpp0.5v5 linux-headers-4.15.0-13 linux-headers-4.15.0-13-generic linux-headers-4.15.0-15
  linux-headers-4.15.0-15-generic linux-image-4.15.0-13-generic linux-image-4.15.0-15-generic linux-image-extra-4.15.0-13-generic linux-image-extra-4.15.0-15-generic linux-signed-image-4.15.0-15-generic
  mono-4.0-gac mono-gac mono-runtime mono-runtime-common mono-runtime-sgen php-common php-gd php-gmp php-ldap php-mbstring php-mysql php-pear php-php-gettext php-phpseclib php-snmp php-twig php-xml
  php7.2-cli php7.2-common php7.2-gd php7.2-gmp php7.2-json php7.2-ldap php7.2-mbstring php7.2-mysql php7.2-opcache php7.2-readline php7.2-snmp php7.2-xml rrdtool shim snmp
Use 'apt autoremove' to remove them.
The following additional packages will be installed:
  mysql-server-5.7
Suggested packages:
  mailx tinyca
The following packages will be upgraded:
  mysql-server-5.7
1 upgraded, 0 newly installed, 0 to remove and 6 not upgraded.
2 not fully installed or removed.
Need to get 0 B/3.190 kB of archives.
After this operation, 48,1 kB disk space will be freed.
Do you want to continue? [Y/n] Y
Preconfiguring packages ...
(Reading database ... 354086 files and directories currently installed.)
Preparing to unpack .../mysql-server-5.7_5.7.22-0ubuntu18.04.1_amd64.deb ...
Unpacking mysql-server-5.7 (5.7.22-0ubuntu18.04.1) over (5.7.21-1ubuntu1) ...
Processing triggers for ureadahead (0.100.0-20) ...
Setting up mysql-server-core-5.7 (5.7.22-0ubuntu18.04.1) ...
Processing triggers for systemd (237-3ubuntu10) ...
Processing triggers for man-db (2.8.3-2) ...
Setting up mysql-server-5.7 (5.7.22-0ubuntu18.04.1) ...
Checking if update is needed.
Checking server version.
Running queries to upgrade MySQL server.
Checking system database.
mysql.columns_priv OK
mysql.db OK
mysql.engine_cost OK
mysql.event OK
mysql.func OK
mysql.general_log OK
mysql.gtid_executed OK
mysql.help_category OK
mysql.help_keyword OK
mysql.help_relation OK
mysql.help_topic OK
mysql.innodb_index_stats OK
mysql.innodb_table_stats OK
mysql.ndb_binlog_index OK
mysql.plugin OK
mysql.proc OK
mysql.procs_priv OK
mysql.proxies_priv OK
mysql.server_cost OK
mysql.servers OK
mysql.slave_master_info OK
mysql.slave_relay_log_info OK
mysql.slave_worker_info OK
mysql.slow_log OK
mysql.tables_priv OK
mysql.time_zone OK
mysql.time_zone_leap_second OK
mysql.time_zone_name OK
mysql.time_zone_transition OK
mysql.time_zone_transition_type OK
mysql.user OK
The sys schema is already up to date (version 1.5.1).
Checking databases.
sys.sys_config OK
Upgrade process completed successfully.
Checking if update is needed.