apt-get -f install
Reading package lists... Done
Building dependency tree
Reading state information... Done
Correcting dependencies... Done
The following extra packages will be installed:
  mysql-server-5.5
Suggested packages:
  tinyca mailx
The following NEW packages will be installed:
  mysql-server-5.5
0 upgraded, 1 newly installed, 0 to remove and 15 not upgraded.
19 not fully installed or removed.
Need to get 1,744 kB of archives.
After this operation, 32.7 MB of additional disk space will be used.
Do you want to continue? [Y/n] y
Get:1 http://us.archive.ubuntu.com/ubuntu/ trusty-updates/main mysql-server-5.5 amd64 5.5.41-0ubuntu0.14.04.1 [1,744 kB]
Fetched 1,744 kB in 0s (5,515 kB/s)
Preconfiguring packages ...
(Reading database ... 263775 files and directories currently installed.)
Preparing to unpack .../mysql-server-5.5_5.5.41-0ubuntu0.14.04.1_amd64.deb ...
Aborting downgrade from (at least) 5.6 to 5.5.
If are sure you want to downgrade to 5.5, remove the file
/var/lib/mysql/debian-*.flag and try installing again.
dpkg: error processing archive /var/cache/apt/archives/mysql-server-5.5_5.5.41-0ubuntu0.14.04.1_amd64.deb (--unpack):
 subprocess new pre-installation script returned error exit status 1
Errors were encountered while processing:
 /var/cache/apt/archives/mysql-server-5.5_5.5.41-0ubuntu0.14.04.1_amd64.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)