Comment 0 for bug 1474212

Not sure if it's relevant, by my mariadb data dir is on a secondary hard drive. /var/lib/mysql-upgrade/DATADIR.link points to the right path.

This is the terminal output for apt-get dist-upgrade:

Selecting previously unselected package mariadb-server-10.0.
(Reading database ... 274672 files and directories currently installed.)
Preparing to unpack .../mariadb-server-10.0_10.0.20-0ubuntu0.15.04.1_amd64.deb ...
cp: cannot overwrite directory ‘/var/lib/mysql-upgrade/DATADIR.link/mysql’ with non-directory
dpkg: error processing archive /var/cache/apt/archives/mariadb-server-10.0_10.0.20-0ubuntu0.15.04.1_amd64.deb (--unpack):
 subprocess new pre-installation script returned error exit status 1
+ . /usr/share/debconf/confmodule
++ '[' '!' '' ']'
++ PERL_DL_NONLAZY=1
++ export PERL_DL_NONLAZY
++ '[' '' ']'
++ exec /usr/share/debconf/frontend /var/lib/dpkg/info/mariadb-server-10.0.postinst abort-upgrade 10.0.20-0ubuntu0.15.04.1
+ . /usr/share/debconf/confmodule
++ '[' '!' 1 ']'
++ '[' -z '' ']'
++ exec
++ '[' '' ']'
++ exec
++ DEBCONF_REDIR=1
++ export DEBCONF_REDIR
+ '[' -n '' ']'
+ export PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/sbin:/usr/sbin:/bin:/usr/bin
+ PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/sbin:/usr/sbin:/bin:/usr/bin
+ ERR_LOGGER='logger -p daemon.err -t mysqld_safe -i'
+ set -o pipefail
+ MYSQL_BOOTSTRAP='/usr/sbin/mysqld --bootstrap --user=mysql --skip-grant-tables --default-storage-engine=myisam --plugin-load-add=auth_socket'
+ set +e
+ invoke stop
+ '[' -x /usr/sbin/invoke-rc.d ']'
+ invoke-rc.d mysql stop
+ set -e
+ case "$1" in
+ '[' abort-upgrade = configure ']'
+ db_stop
+ echo STOP
+ '[' -x /etc/init.d/mysql ']'
+ update-rc.d mysql defaults 19 21
+ '[' -x /etc/init.d/mysql ']'
+ echo 'Invoking mysql start'
+ logger -p daemon.err -t mysqld_safe -i
+ invoke-rc.d mysql start
+ exit 0
Preparing to unpack .../mariadb-server_10.0.20-0ubuntu0.15.04.1_all.deb ...
Unpacking mariadb-server (10.0.20-0ubuntu0.15.04.1) over (10.0.17-0ubuntu1) ...
Errors were encountered while processing:
 /var/cache/apt/archives/mariadb-server-10.0_10.0.20-0ubuntu0.15.04.1_amd64.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)

ProblemType: Package
DistroRelease: Ubuntu 15.04
Package: mariadb-server-10.0 10.0.17-0ubuntu1
ProcVersionSignature: Ubuntu 3.19.0-22.22-generic 3.19.8-ckt1
Uname: Linux 3.19.0-22-generic x86_64
ApportVersion: 2.17.2-0ubuntu1.1
Architecture: amd64
Date: Tue Jul 14 08:07:15 2015
DpkgTerminalLog:
 Preparing to unpack .../mariadb-server-10.0_10.0.20-0ubuntu0.15.04.1_amd64.deb ...
 cp: cannot overwrite directory ‘/var/lib/mysql-upgrade/DATADIR.link/mysql’ with non-directory
 dpkg: error processing archive /var/cache/apt/archives/mariadb-server-10.0_10.0.20-0ubuntu0.15.04.1_amd64.deb (--unpack):
  subprocess new pre-installation script returned error exit status 1
DuplicateSignature: package:mariadb-server-10.0:10.0.17-0ubuntu1:subprocess new pre-installation script returned error exit status 1
ErrorMessage: subprocess new pre-installation script returned error exit status 1
InstallationDate: Installed on 2015-01-15 (180 days ago)
InstallationMedia: Ubuntu 14.10 "Utopic Unicorn" - Release amd64 (20141022.1)
RelatedPackageVersions:
 dpkg 1.17.25ubuntu1
 apt 1.0.9.7ubuntu4
SourcePackage: mariadb-10.0
Title: package mariadb-server-10.0 10.0.17-0ubuntu1 failed to install/upgrade: subprocess new pre-installation script returned error exit status 1
UpgradeStatus: Upgraded to vivid on 2015-05-27 (47 days ago)