При sudo apt-get purge mysql-server
Зависает на Renaming removed key_buffer and myisam-recover options (if present)
лог
$ sudo apt-get purge mysql-server
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package 'mysql-server' is not installed, so not removed
The following packages were automatically installed and are no longer required:
libaio1 linux-headers-4.4.0-59 linux-headers-4.4.0-59-generic linux-headers-4.4.0-62 linux-headers-4.4.0-62-generic linux-headers-4.4.0-63
linux-headers-4.4.0-63-generic linux-headers-4.4.0-64 linux-headers-4.4.0-64-generic linux-headers-4.4.0-65 linux-headers-4.4.0-65-generic
linux-headers-4.4.0-66 linux-headers-4.4.0-66-generic linux-headers-4.4.0-70 linux-headers-4.4.0-70-generic linux-image-4.4.0-59-generic
linux-image-4.4.0-62-generic linux-image-4.4.0-63-generic linux-image-4.4.0-64-generic linux-image-4.4.0-65-generic linux-image-4.4.0-66-generic
linux-image-4.4.0-70-generic linux-image-extra-4.4.0-59-generic linux-image-extra-4.4.0-62-generic linux-image-extra-4.4.0-63-generic
linux-image-extra-4.4.0-64-generic linux-image-extra-4.4.0-65-generic linux-image-extra-4.4.0-66-generic linux-image-extra-4.4.0-70-generic
mysql-client-5.7 mysql-client-core-5.7 mysql-common mysql-server-5.7 mysql-server-core-5.7
Use 'sudo apt autoremove' to remove them.
0 upgraded, 0 newly installed, 0 to remove and 97 not upgraded.
1 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Setting up mysql-server-5.7 (5.7.17-0ubuntu0.16.04.2) ...
Renaming removed key_buffer and myisam-recover options (if present)
Ничего из того что было в интернете не помогло. Но переустановку системы я пока исключаю.