Ubuntu upgrade from 14.04 LTS to 16.04 failed - mysql-server-5.7 dependecies fail
I am trying to upgrade existing Ubuntu 14.04 LTS to Ubuntu 16.04 LTS and it seems I am stuck somewhere in the middle. When I turn on my workstation, I get Ubuntu 16.04 LTS welcome & login screen, which is ok, newest kernel is up and running however, when I do sudo apt-get update && sudo apt-get upgrade && sudo apt-get dist-upgrade && sudo apt-get
autoremove and then press Y/y to confirm upgrade, I get:
user@work002:~$ sudo apt-get update && sudo apt-get upgrade && sudo apt-get dist-upgrade && sudo apt-get autoremove
Get:1 http://si.archive.ubuntu.com/ubuntu xenial InRelease [247 kB]
Hit:2 http://archive.canonical.com/ubuntu xenial InRelease
Hit:3 http://security.ubuntu.com/ubuntu xenial-security InRelease
Hit:4 http://si.archive.ubuntu.com/ubuntu xenial-updates InRelease
Hit:5 http://archive.canonical.com xenial InRelease
Hit:6 http://si.archive.ubuntu.com/ubuntu xenial-backports InRelease
Fetched 247 kB in 0s (319 kB/s)
Reading package lists... Done
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages were automatically installed and are no longer required:
account-plugin-twitter bluez-gstreamer bsh calculix-ccx checkbox-ng comerr-dev dh-apparmor firefox-locale-he firefox-locale-ru firefox-locale-sl fonts-unfonts-core friends friends-dispatcher
friends-facebook friends-twitter g++-4.8 gcc-4.9-base:i386 gcj-4.8-jre-lib gir1.2-ebook-1.2 gir1.2-ebookcontacts-1.2 gir1.2-edataserver-1.2 gir1.2-gnomebluetooth-1.0 gir1.2-messagingmenu-1.0
gir1.2-networkmanager-1.0 gstreamer0.10-pulseaudio gstreamer1.0-clutter gtk3-engines-unico heirloom-mailx icedtea-netx icedtea-netx-common iproute jetty jsvc ko.tex-extra-hlfont krb5-multidev
kubuntu-debug-installer latex-sanskrit libass4 libatk-wrapper-java libatk-wrapper-java-jni libavcodec54 libavformat54 libavutil52 libbaloocore4 libbaloofiles4 libbalooxapian4 libbasicusageenvironment0
libbetter-appframework-java libbind9-90 libboost-date-time1.54.0 libboost-program-options1.55.0 libboost-python1.55.0 libboost-regex1.55.0 libboost-signals1.55.0 libboost-system1.54.0
libboost-system1.55.0 libcamel-1.2-45 libcdr-0.0-0 libcglib-java libclutter-gst-2.0-0 libcmis-0.4-4 libcolord1 libcolorhug1 libcommons-daemon-java libcr0 libcrypt-passwdmd5-perl libcxsparse3.1.2
libdb-java libdb-je-java libdb5.3-java libdb5.3-java-jni libdbd-mysql-perl libdbi-perl libdbus-1-3:i386 libdirac-encoder0 libdns100 libdrm2:i386 libdvbpsi8 libeasymock-java libebackend-1.2-7
libebook-1.2-14 libebook-contacts-1.2-0 libedata-book-1.2-20 libedataserver-1.2-18 libegl1-mesa-lts-vivid libelfg0 libenca0 libepub0 libetpan15 libexiv2-12 libflute-java libfriends0 libgbm1-lts-vivid
libgcj-bc libgcj14 libgconf2-4 libgdata13 libgee2 libgeos-3.4.2 libgif4 libgl1-mesa-dri-lts-vivid libgl1-mesa-glx-lts-vivid libglapi-mesa-lts-vivid libgles1-mesa-lts-vivid libgles2-mesa-lts-vivid
libglew1.10 libglewmx1.10 libgnome-bluetooth11 libgnome-desktop-3-7 libgnutls-dev libgnutlsxx27 libgphoto2-port10 libgraphicsmagick++3 libgraphicsmagick3 libgrip0 libgroupsock1 libgtksourceview2.0-0
libgtksourceview2.0-common libgtop2-7 libhdf5-7 libicc2 libicu52 libidl-common libimdi0 libimobiledevice4 libintl-perl libisc95 libisccc90 libisccfg90 libisl10 libjavascriptcoregtk-1.0-0 libjetty-java
libjline-java libjs-codemirror libjs-jquery-cookie libjs-jquery-event-drag libjs-jquery-metadata libjs-jquery-mousewheel libjs-jquery-tablesorter libjs-jquery-ui libjson-c2:i386 libjtidy-java
libkactivities-models1 libkadm5clnt-mit9 libkadm5srv-mit9 libkidletime4 libkrb5-dev liblcms1 liblinear1 liblivemedia23 liblouis2 liblucene2-java liblwres90 libmagick++5 libmagickcore5
libmagickcore5-extra libmagickwand5 libmbim-glib0 libminiupnpc8 libmspub-0.0-0 libmysqlclient18 libnb-platform13-java libnepomukcleaner4 libnepomukcore4abi1 libnetcdfc7 libnetx-java libnih-dbus1:i386
libnih1:i386 libobjc-4.8-dev liboctave2 libopenjpeg2 liborbit2 liborcus-0.6-0 libp11-kit-dev libpanel-applet-4-0 libparted0debian1 libplist1 libpng12-0:i386 libpocketsphinx1 libpoppler-qt4-4 libpoppler44
libpostproc52 libprotobuf8 libqhull6 libqjson0 libqmi-glib0 libqmobipocket1 libqpdf13 libqscintilla2-11 libqt5qml-graphicaleffects libqt5sensors5 libqt5webkit5-qmlwebkitplugin libraw9 librpmsign1
librtaudio4 librtmidi1 librtmp0 libsac-java libsac-java-gcj libsctp1 libsexy2 libsoprano4 libsoqt4-20 libsphinxbase1 libspnav0 libspooles2.2 libstdc++-4.8-dev libstk0c2a libswingx1-java libswscale2
libsystemd-daemon0 libsystemd-journal0 libsystemd-login0 libt1-5 libtar0 libtasn1-6-dev libterm-readkey-perl libthumbnailer0 libtorque2 libts-0.0-0 libunityvoice1 libupower-glib1 libusageenvironment1
libusbmuxd2 libvirtodbc0 libvisio-0.0-0 libwebkitgtk-1.0-0 libwebkitgtk-1.0-common libwireshark3 libwiretap3 libwnck-common libwnck22 libwpd-0.9-9 libwpg-0.2-2 libwps-0.2-2 libwsutil3 libwxgtk-media2.8-0
libx264-142 libxatracker2-lts-vivid libxcb-util0 libxtables10 libzip2 libzipios++0c2a linux-headers-generic-lts-vivid linux-image-generic-lts-vivid lksctp-tools nepomuk-core-data obex-data-server
openjdk-7-doc perlmagick phonon-backend-gstreamer1.0 php5-gd php5-mysql php5-pgsql python-collada python-commandnotfound python-dateutil python-dbus-dev python-gconf python-gdbm python-gnome2
python-gnomekeyring python-gobject python-gtksourceview2 python-ibus python-imaging-tk python-libxml2 python-matplotlib python-matplotlib-data python-notify python-pivy python-pyorbit python-pyparsing
python-qt4-gl python-requests python-smbc python-support python-wxgtk2.8 python3-checkbox-ng qapt-batch qtdeclarative5-dialogs-plugin qtdeclarative5-localstorage-plugin
qtdeclarative5-privatewidgets-plugin qtdeclarative5-qtfeedback-plugin qtdeclarative5-ubuntu-ui-extras-browser-plugin qtdeclarative5-ubuntu-ui-extras-browser-plugin-assets qtdeclarative5-window-plugin
shared-desktop-ontologies signon-keyring-extension soprano-daemon sphinx-voxforge-hmm-en sphinx-voxforge-lm-en swath syslinux-themes-debian syslinux-themes-debian-wheezy telepathy-indicator tsconf
ttf-dejavu-core ttf-dejavu-extra ubuntu-extras-keyring unity-lens-friends unity-scope-audacious unity-scope-clementine unity-scope-gmusicbrowser unity-scope-gourmet unity-scope-guayadeque
unity-scope-musique unity-voice-service unixodbc virtuoso-minimal virtuoso-opensource-6.1-bin virtuoso-opensource-6.1-common xchat-common xfonts-mathml xserver-xorg-input-evdev-lts-vivid
xserver-xorg-input-mouse-lts-vivid xserver-xorg-input-synaptics-lts-vivid xserver-xorg-input-vmmouse-lts-vivid xserver-xorg-input-wacom-lts-vivid xserver-xorg-video-ati-lts-vivid
xserver-xorg-video-cirrus-lts-vivid xserver-xorg-video-fbdev-lts-vivid xserver-xorg-video-intel-lts-vivid xserver-xorg-video-mach64-lts-vivid xserver-xorg-video-mga-lts-vivid
xserver-xorg-video-neomagic-lts-vivid xserver-xorg-video-nouveau-lts-vivid xserver-xorg-video-openchrome-lts-vivid xserver-xorg-video-r128-lts-vivid xserver-xorg-video-radeon-lts-vivid
xserver-xorg-video-savage-lts-vivid xserver-xorg-video-siliconmotion-lts-vivid xserver-xorg-video-sisusb-lts-vivid xserver-xorg-video-tdfx-lts-vivid xserver-xorg-video-trident-lts-vivid
xserver-xorg-video-vesa-lts-vivid xserver-xorg-video-vmware-lts-vivid
Use 'sudo apt autoremove' to remove them.
The following packages have been kept back:
libjpeg-turbo-progs
0 upgraded, 0 newly installed, 0 to remove and 1 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] y
Setting up mysql-server-5.7 (5.7.11-0ubuntu6) ...
Job for mysql.service failed because the control process exited with error code. See "systemctl status mysql.service" and "journalctl -xe" for details.
invoke-rc.d: initscript mysql, action "start" failed.
No apport report written because the error message indicates its a followup error from a previous failure.
dpkg: error processing package mysql-server-5.7 (--configure):
subprocess installed post-installation script returned error exit status 1
dpkg: dependency problems prevent configuration of mysql-server:
mysql-server depends on mysql-server-5.7; however:
Package mysql-server-5.7 is not configured yet.
dpkg: error processing package mysql-server (--configure):
dependency problems - leaving unconfigured
Errors were encountered while processing:
mysql-server-5.7
mysql-server
E: Sub-process /usr/bin/dpkg returned an error code (1)
When I inspect error with systemctl status mysql.service, I get:
user@work002:~$ systemctl status mysql.service
● mysql.service - MySQL Community Server
Loaded: loaded (/lib/systemd/system/mysql.service; enabled; vendor preset: enabled)
Active: activating (start-post) (Result: exit-code) since pet 2016-04-22 19:38:49 CEST; 12s ago
Process: 10171 ExecStart=/usr/sbin/mysqld (code=exited, status=1/FAILURE)
Process: 10168 ExecStartPre=/usr/share/mysql/mysql-systemd-start pre (code=exited, status=0/SUCCESS)
Main PID: 10171 (code=exited, status=1/FAILURE); : 10172 (mysql-systemd-s)
Tasks: 2 (limit: 512)
CGroup: /system.slice/mysql.service
└─control
├─10172 /bin/bash /usr/share/mysql/mysql-systemd-start post
└─10239 sleep 1
apr 22 19:38:49 work002 systemd[1]: Starting MySQL Community Server...
apr 22 19:38:51 work002 systemd[1]: mysql.service: Main process exited, code=exited, status=1/FAILURE
and with journalctl -xe I get:
user@work002:~$ journalctl -xe
apr 22 19:41:27 work002 systemd[1]: Stopped MySQL Community Server.
-- Subject: Unit mysql.service has finished shutting down
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit mysql.service has finished shutting down.
apr 22 19:41:27 work002 systemd[1]: Starting MySQL Community Server...
-- Subject: Unit mysql.service has begun start-up
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit mysql.service has begun starting up.
apr 22 19:41:29 work002 systemd[1]: mysql.service: Main process exited, code=exited, status=1/FAILURE
apr 22 19:41:57 work002 systemd[1]: Failed to start MySQL Community Server.
-- Subject: Unit mysql.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit mysql.service has failed.
--
-- The result is failed.
apr 22 19:41:57 work002 systemd[1]: mysql.service: Unit entered failed state.
apr 22 19:41:57 work002 systemd[1]: mysql.service: Failed with result 'exit-code'.
apr 22 19:41:57 work002 systemd[1]: mysql.service: Service hold-off time over, scheduling restart.
apr 22 19:41:57 work002 systemd[1]: Stopped MySQL Community Server.
-- Subject: Unit mysql.service has finished shutting down
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit mysql.service has finished shutting down.
apr 22 19:41:57 work002 systemd[1]: Starting MySQL Community Server...
-- Subject: Unit mysql.service has begun start-up
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit mysql.service has begun starting up.
apr 22 19:41:59 work002 systemd[1]: mysql.service: Main process exited, code=exited, status=1/FAILURE
apr 22 19:42:27 work002 systemd[1]: Failed to start MySQL Community Server.
-- Subject: Unit mysql.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit mysql.service has failed.
--
-- The result is failed.
apr 22 19:42:27 work002 systemd[1]: mysql.service: Unit entered failed state.
apr 22 19:42:27 work002 systemd[1]: mysql.service: Failed with result 'exit-code'.
apr 22 19:42:28 work002 systemd[1]: mysql.service: Service hold-off time over, scheduling restart.
apr 22 19:42:28 work002 systemd[1]: Stopped MySQL Community Server.
-- Subject: Unit mysql.service has finished shutting down
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit mysql.service has finished shutting down.
apr 22 19:42:28 work002 systemd[1]: Starting MySQL Community Server...
-- Subject: Unit mysql.service has begun start-up
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit mysql.service has begun starting up.
apr 22 19:42:30 work002 systemd[1]: mysql.service: Main process exited, code=exited, status=1/FAILURE
I've made offline databases(s) backup by copying files from /var/lib/mysql since I cannot connect to mysql server and export SQL scripts. How do I overcome this problem to complete upgrade to Ubuntu 16.04 LTS?
I am also adding output of tail -n60 /var/log/mysql/error.log:
2016-04-22T21:45:57.355858Z 0 [Note] InnoDB: Loading buffer pool(s) from /var/lib/mysql/ib_buffer_pool
2016-04-22T21:45:57.355908Z 0 [Note] Plugin 'FEDERATED' is disabled.
2016-04-22T21:45:57.356069Z 0 [Note] InnoDB: Buffer pool(s) load completed at 160422 23:45:57
2016-04-22T21:45:57.356321Z 0 [Warning] System table 'plugin' is expected to be transactional.
2016-04-22T21:45:57.356485Z 0 [ERROR] unknown variable 'key_buffer=16M'
2016-04-22T21:45:57.356498Z 0 [ERROR] Aborting
2016-04-22T21:45:57.356507Z 0 [Note] Binlog end
2016-04-22T21:45:57.356551Z 0 [Note] Shutting down plugin 'ngram'
2016-04-22T21:45:57.356560Z 0 [Note] Shutting down plugin 'ARCHIVE'
2016-04-22T21:45:57.356565Z 0 [Note] Shutting down plugin 'partition'
2016-04-22T21:45:57.356570Z 0 [Note] Shutting down plugin 'BLACKHOLE'
2016-04-22T21:45:57.356576Z 0 [Note] Shutting down plugin 'INNODB_SYS_VIRTUAL'
2016-04-22T21:45:57.356581Z 0 [Note] Shutting down plugin 'INNODB_SYS_DATAFILES'
2016-04-22T21:45:57.356586Z 0 [Note] Shutting down plugin 'INNODB_SYS_TABLESPACES'
2016-04-22T21:45:57.356591Z 0 [Note] Shutting down plugin 'INNODB_SYS_FOREIGN_COLS'
2016-04-22T21:45:57.356595Z 0 [Note] Shutting down plugin 'INNODB_SYS_FOREIGN'
2016-04-22T21:45:57.356600Z 0 [Note] Shutting down plugin 'INNODB_SYS_FIELDS'
2016-04-22T21:45:57.356605Z 0 [Note] Shutting down plugin 'INNODB_SYS_COLUMNS'
2016-04-22T21:45:57.356610Z 0 [Note] Shutting down plugin 'INNODB_SYS_INDEXES'
2016-04-22T21:45:57.356615Z 0 [Note] Shutting down plugin 'INNODB_SYS_TABLESTATS'
2016-04-22T21:45:57.356620Z 0 [Note] Shutting down plugin 'INNODB_SYS_TABLES'
2016-04-22T21:45:57.356624Z 0 [Note] Shutting down plugin 'INNODB_FT_INDEX_TABLE'
2016-04-22T21:45:57.356629Z 0 [Note] Shutting down plugin 'INNODB_FT_INDEX_CACHE'
2016-04-22T21:45:57.356634Z 0 [Note] Shutting down plugin 'INNODB_FT_CONFIG'
2016-04-22T21:45:57.356639Z 0 [Note] Shutting down plugin 'INNODB_FT_BEING_DELETED'
2016-04-22T21:45:57.356644Z 0 [Note] Shutting down plugin 'INNODB_FT_DELETED'
2016-04-22T21:45:57.356649Z 0 [Note] Shutting down plugin 'INNODB_FT_DEFAULT_STOPWORD'
2016-04-22T21:45:57.356687Z 0 [Note] Shutting down plugin 'INNODB_METRICS'
2016-04-22T21:45:57.356695Z 0 [Note] Shutting down plugin 'INNODB_TEMP_TABLE_INFO'
2016-04-22T21:45:57.356700Z 0 [Note] Shutting down plugin 'INNODB_BUFFER_POOL_STATS'
2016-04-22T21:45:57.356705Z 0 [Note] Shutting down plugin 'INNODB_BUFFER_PAGE_LRU'
2016-04-22T21:45:57.356710Z 0 [Note] Shutting down plugin 'INNODB_BUFFER_PAGE'
2016-04-22T21:45:57.356715Z 0 [Note] Shutting down plugin 'INNODB_CMP_PER_INDEX_RESET'
2016-04-22T21:45:57.356719Z 0 [Note] Shutting down plugin 'INNODB_CMP_PER_INDEX'
2016-04-22T21:45:57.356724Z 0 [Note] Shutting down plugin 'INNODB_CMPMEM_RESET'
2016-04-22T21:45:57.356729Z 0 [Note] Shutting down plugin 'INNODB_CMPMEM'
2016-04-22T21:45:57.356734Z 0 [Note] Shutting down plugin 'INNODB_CMP_RESET'
2016-04-22T21:45:57.356739Z 0 [Note] Shutting down plugin 'INNODB_CMP'
2016-04-22T21:45:57.356743Z 0 [Note] Shutting down plugin 'INNODB_LOCK_WAITS'
2016-04-22T21:45:57.356748Z 0 [Note] Shutting down plugin 'INNODB_LOCKS'
2016-04-22T21:45:57.356753Z 0 [Note] Shutting down plugin 'INNODB_TRX'
2016-04-22T21:45:57.356757Z 0 [Note] Shutting down plugin 'InnoDB'
2016-04-22T21:45:57.356886Z 0 [Note] InnoDB: FTS optimize thread exiting.
2016-04-22T21:45:57.357160Z 0 [Note] InnoDB: Starting shutdown...
2016-04-22T21:45:57.457470Z 0 [Note] InnoDB: Dumping buffer pool(s) to /var/lib/mysql/ib_buffer_pool
2016-04-22T21:45:57.457683Z 0 [Note] InnoDB: Buffer pool(s) dump completed at 160422 23:45:57
2016-04-22T21:45:58.975431Z 0 [Note] InnoDB: Shutdown completed; log sequence number 17597621
2016-04-22T21:45:58.978042Z 0 [Note] InnoDB: Removed temporary tablespace data file: "ibtmp1"
2016-04-22T21:45:58.978060Z 0 [Note] Shutting down plugin 'MEMORY'
2016-04-22T21:45:58.978068Z 0 [Note] Shutting down plugin 'PERFORMANCE_SCHEMA'
2016-04-22T21:45:58.978124Z 0 [Note] Shutting down plugin 'MRG_MYISAM'
2016-04-22T21:45:58.978130Z 0 [Note] Shutting down plugin 'MyISAM'
2016-04-22T21:45:58.978137Z 0 [Note] Shutting down plugin 'CSV'
2016-04-22T21:45:58.978143Z 0 [Note] Shutting down plugin 'sha256_password'
2016-04-22T21:45:58.978148Z 0 [Note] Shutting down plugin 'mysql_native_password'
2016-04-22T21:45:58.978153Z 0 [Note] Shutting down plugin 'keyring_file'
2016-04-22T21:45:58.978369Z 0 [Note] Shutting down plugin 'binlog'
2016-04-22T21:45:58.978540Z 0 [Note] /usr/sbin/mysqld: Shutdown complete
And I am also adding dpkg -l|grep mysql output:
ii dbconfig-mysql 2.0.4ubuntu1 all dbconfig-common MySQL/MariaDB support
ii libdbd-mysql-perl 4.033-1build2 amd64 Perl5 database interface to the MySQL database
ii libmysql-java 5.1.38-1 all Java database (JDBC) driver for MySQL
ii libmysqlclient-dev 5.7.11-0ubuntu6 amd64 MySQL database development files
ii libmysqlclient18:amd64 5.5.49-0ubuntu0.14.04.1 amd64 MySQL database client library
ii libmysqlclient20:amd64 5.7.11-0ubuntu6 amd64 MySQL database client library
rc libmysqlcppconn7 1.1.3-5 amd64 MySQL Connector for C++ (library)
ii libmysqlcppconn7v5 1.1.7-0ubuntu1 amd64 MySQL Connector for C++ (library)
ii mysql-client-5.7 5.7.11-0ubuntu6 amd64 MySQL database client binaries
ii mysql-client-core-5.7 5.7.11-0ubuntu6 amd64 MySQL database core client binaries
ii mysql-common 5.7.11-0ubuntu6 all MySQL database common files, e.g. /etc/mysql/my.cnf
iU mysql-server 5.7.11-0ubuntu6 all MySQL database server (metapackage depending on the latest version)
rc mysql-server-5.5 5.5.49-0ubuntu0.14.04.1 amd64 MySQL database server binaries and system database setup
hF mysql-server-5.7 5.7.11-0ubuntu6 amd64 MySQL database server binaries and system database setup
ii mysql-server-core-5.7 5.7.11-0ubuntu6 amd64 MySQL database server binaries
ii mysql-utilities 1.6.1-2 all collection of scripts for managing MySQL servers
ii mysql-workbench 6.3.6+dfsg-0ubuntu1 amd64 MySQL Workbench - a visual database modeling, administration and queuing tool
rc mysql-workbench-community 6.3.6-1ubu1404 amd64 MySQL Workbench
ii mysql-workbench-data 6.3.6+dfsg-0ubuntu1 all MySQL Workbench -- architecture independent data
ii php-mysql 1:7.0+35ubuntu6 all MySQL module for PHP [default]
ii php5-mysql 5.5.9+dfsg-1ubuntu4.16 amd64 MySQL module for php5
rc php5-mysqlnd 5.5.9+dfsg-1ubuntu4.14 amd64 MySQL module for php5 (Native Driver)
ii php7.0-mysql 7.0.4-7ubuntu2 amd64 MySQL module for PHP
ii python-mysql.connector 2.0.4-1 all pure Python implementation of MySQL Client/Server protocol
Solution 1:
Have you checked: https://bugs.launchpad.net/ubuntu/+source/mysql-5.7/+bug/1571865 (linked from the XenialXerus release notes at https://wiki.ubuntu.com/XenialXerus/ReleaseNotes#MySQL_5.7)?
It explains that due to changes in the name of some configuration directives, starting mysql fails. It also mentions three solutions, the first of which solved my problem.
Solution 2:
After a lot of wrangling, the thing that finally fixed this for me was simply to create a missing /etc/mysql/conf.d/ directory (ie. sudo mkdir /etc/mysql/conf.d/). There was a /etc/mysql/mysql.conf.d/ directory, but MySQL seemed to be looking for a conf.d directory too, and its absence seemed to be preventing it starting. Once I'd created the directory sudo service mysql start worked and all was ok.
In case it's of use, running the command journalctl -xe and looking carefully through the log that it outputs was how I found the "missing directory" error.