Upgrade from Debian's 10.0 packages to MariaDB's 10.1 packages fails

• install MariaDB from Debian's repo:

  sudo apt-get install mariadb-server mariadb-client mariadb-test

  ...

  Get:1 http://security.debian.org/ jessie/updates/main mysql-common all 5.5.54-0+deb8u1 [81.2 kB]

  Get:2 http://debian.osuosl.org/debian/ jessie/main perl amd64 5.20.2-3+deb8u6 [2,637 kB]

  Get:3 http://security.debian.org/ jessie/updates/main libmysqlclient18 amd64 5.5.54-0+deb8u1 [673 kB]

  Get:4 http://security.debian.org/ jessie/updates/main mariadb-common all 10.0.29-0+deb8u1 [17.1 kB]

  Get:5 http://security.debian.org/ jessie/updates/main mariadb-client-core-10.0 amd64 10.0.29-0+deb8u1 [801 kB]

  Get:6 http://security.debian.org/ jessie/updates/main mariadb-client-10.0 amd64 10.0.29-0+deb8u1 [1,158 kB]

  Get:7 http://security.debian.org/ jessie/updates/main mariadb-server-core-10.0 amd64 10.0.29-0+deb8u1 [4,706 kB]

  Get:8 http://security.debian.org/ jessie/updates/main mariadb-server-10.0 amd64 10.0.29-0+deb8u1 [5,966 kB]

  Get:9 http://security.debian.org/ jessie/updates/main mariadb-client all 10.0.29-0+deb8u1 [16.7 kB]

  Get:10 http://security.debian.org/ jessie/updates/main mariadb-server all 10.0.29-0+deb8u1 [16.8 kB]

  Get:11 http://security.debian.org/ jessie/updates/main mariadb-test-10.0 amd64 10.0.29-0+deb8u1 [30.6 MB]

  Get:12 http://security.debian.org/ jessie/updates/main mariadb-test all 10.0.29-0+deb8u1 [16.6 kB]

  Get:13 http://debian.osuosl.org/debian/ jessie/main perl-base amd64 5.20.2-3+deb8u6 [1,229 kB]

  Get:14 http://debian.osuosl.org/debian/ jessie/main perl-modules all 5.20.2-3+deb8u6 [2,547 kB]

  Get:15 http://debian.osuosl.org/debian/ jessie/main libreadline5 amd64 5.2+dfsg-2 [151 kB]

  Get:16 http://debian.osuosl.org/debian/ jessie/main libdbi-perl amd64 1.631-3+b1 [816 kB]

  Get:17 http://debian.osuosl.org/debian/ jessie/main libterm-readkey-perl amd64 2.32-1+b1 [28.0 kB]

  Get:18 http://debian.osuosl.org/debian/ jessie/main libdbd-mysql-perl amd64 4.028-2+deb8u2 [119 kB]

  Get:19 http://debian.osuosl.org/debian/ jessie/main libhtml-template-perl all 2.95-1 [66.8 kB]

  ...

• enable MariaDB repo:

  deb http://mirror2.hs-esslingen.de/mariadb/repo/10.1/debian jessie main

• install MariaDB's packages

  sudo apt-get install mariadb-server mariadb-client mariadb-test

  ...

  Get:1 http://mirror2.hs-esslingen.de/mariadb/repo/10.1/debian/ jessie/main mariadb-client all 10.1.21+maria-1~jessie [2,842 B]

  Get:2 http://mirror2.hs-esslingen.de/mariadb/repo/10.1/debian/ jessie/main mariadb-test all 10.1.21+maria-1~jessie [2,784 B]

  Get:3 http://debian.osuosl.org/debian/ jessie/main libmpfr4 amd64 3.1.2-2 [527 kB]

  Get:4 http://mirror2.hs-esslingen.de/mariadb/repo/10.1/debian/ jessie/main galera-3 amd64 25.3.19-jessie [7,528 kB]

  Get:5 http://mirror2.hs-esslingen.de/mariadb/repo/10.1/debian/ jessie/main libmysqlclient18 amd64 10.1.21+maria-1~jessie [2,942 B]

  Get:6 http://mirror2.hs-esslingen.de/mariadb/repo/10.1/debian/ jessie/main mariadb-common all 10.1.21+maria-1~jessie [3,274 B]

  Get:7 http://mirror2.hs-esslingen.de/mariadb/repo/10.1/debian/ jessie/main libmariadbclient18 amd64 10.1.21+maria-1~jessie [585 kB]

  Get:8 http://mirror2.hs-esslingen.de/mariadb/repo/10.1/debian/ jessie/main mariadb-server all 10.1.21+maria-1~jessie [2,980 B]

  Get:9 http://mirror2.hs-esslingen.de/mariadb/repo/10.1/debian/ jessie/main mariadb-server-core-10.1 amd64 10.1.21+maria-1~jessie [4,399 kB]

  Get:10 http://mirror2.hs-esslingen.de/mariadb/repo/10.1/debian/ jessie/main mariadb-server-10.1 amd64 10.1.21+maria-1~jessie [6,222 kB]

  Get:11 http://mirror2.hs-esslingen.de/mariadb/repo/10.1/debian/ jessie/main mariadb-client-core-10.1 amd64 10.1.21+maria-1~jessie [692 kB]

  Get:12 http://mirror2.hs-esslingen.de/mariadb/repo/10.1/debian/ jessie/main mariadb-client-10.1 amd64 10.1.21+maria-1~jessie [1,107 kB]

  Get:13 http://mirror2.hs-esslingen.de/mariadb/repo/10.1/debian/ jessie/main mariadb-test-10.1 amd64 10.1.21+maria-1~jessie [31.1 MB]

  Get:14 http://debian.osuosl.org/debian/ jessie/main gawk amd64 1:4.1.1+dfsg-1 [520 kB]

  Get:15 http://debian.osuosl.org/debian/ jessie/main iproute all 1:3.16.0-2 [15.5 kB]

  Get:16 http://debian.osuosl.org/debian/ jessie/main rsync amd64 3.1.1-3 [390 kB]

  Get:17 http://debian.osuosl.org/debian/ jessie/main socat amd64 1.7.2.4-2 [333 kB]

  Setting up mariadb-server-10.1 (10.1.21+maria-1~jessie) ...

  Installing new version of config file /etc/init.d/mysql ...

  Installing new version of config file /etc/logrotate.d/mysql-server ...

  Installing new version of config file /etc/mysql/debian-start ...

  Job for mariadb.service failed. See 'systemctl status mariadb.service' and 'journalctl -xn' for details.

  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-test-10.1:

  mariadb-test-10.1 depends on mariadb-server-10.1 (= 10.1.21+maria-1~jessie); however:

  Package mariadb-server-10.1 is not configured yet.

  dpkg: error processing package mariadb-test-10.1 (--configure):

  dependency problems - leaving unconfigured

  dpkg: dependency problems prevent configuration of mariadb-test:

  mariadb-test depends on mariadb-test-10.1 (= 10.1.21+maria-1~jessie); however:

  Package mariadb-test-10.1 is not configured yet.

  dpkg: error processing package mariadb-test (--configure):

  dependency problems - leaving unconfigured

  dpkg: dependency problems prevent configuration of mariadb-server:

  mariadb-server depends on mariadb-server-10.1 (= 10.1.21+maria-1~jessie); however:

  Package mariadb-server-10.1 is not configured yet.

  dpkg: error processing package mariadb-server (--configure):

  dependency problems - leaving unconfigured

  Processing triggers for systemd (215-17) ...

  Processing triggers for libc-bin (2.19-18) ...

  Errors were encountered while processing:

  mariadb-server-10.1

  mariadb-test-10.1

  mariadb-test

  mariadb-server

  E: Sub-process /usr/bin/dpkg returned an error code (1)

The service claims to be down:

buildbot@debian-jessie-amd64:~$ systemctl status mariadb.service

● mariadb.service - MariaDB database server

   Loaded: loaded (/lib/systemd/system/mariadb.service; enabled)

  Drop-In: /etc/systemd/system/mariadb.service.d

           └─migrated-from-my.cnf-settings.conf

   Active: failed (Result: exit-code) since Thu 2017-02-02 11:58:31 EST; 11s ago

 Main PID: 16552 (code=exited, status=1/FAILURE)

   Status: "MariaDB server is down"

The packages are in fact installed:

$ dpkg -l | grep -i maria

ii  libmariadbclient18             10.1.21+maria-1~jessie      amd64        MariaDB database client library

ii  libmysqlclient18               10.1.21+maria-1~jessie      amd64        Virtual package to satisfy external depends

ii  mariadb-client                 10.1.21+maria-1~jessie      all          MariaDB database client (metapackage depending on the latest version)

rc  mariadb-client-10.0            10.0.29-0+deb8u1            amd64        MariaDB database client binaries

ii  mariadb-client-10.1            10.1.21+maria-1~jessie      amd64        MariaDB database client binaries

ii  mariadb-client-core-10.1       10.1.21+maria-1~jessie      amd64        MariaDB database core client binaries

ii  mariadb-common                 10.1.21+maria-1~jessie      all          MariaDB database common files (e.g. /etc/mysql/conf.d/mariadb.cnf)

iU  mariadb-server                 10.1.21+maria-1~jessie      all          MariaDB database server (metapackage depending on the latest version)

rc  mariadb-server-10.0            10.0.29-0+deb8u1            amd64        MariaDB database server binaries

iF  mariadb-server-10.1            10.1.21+maria-1~jessie      amd64        MariaDB database server binaries

ii  mariadb-server-core-10.1       10.1.21+maria-1~jessie      amd64        MariaDB database core server files

iU  mariadb-test                   10.1.21+maria-1~jessie      all          MariaDB database regression test suite (metapackage for the latest version)

iU  mariadb-test-10.1              10.1.21+maria-1~jessie      amd64        MariaDB database regression test suite

And the server is running, but it's still the old one:

Welcome to the MariaDB monitor.  Commands end with ; or \g.

Your MariaDB connection id is 48

Server version: 10.0.29-MariaDB-0+deb8u1 (Debian)

sudo systemctl stop mariadb.service does not do anything. If I stop the server manually, I can then run sudo systemctl start mariadb.service, and it starts the new server all right.