ubuntu@ip-172-31-45-140:~$ sudo apt-get remove --purge mysql-server mysql-client mysql-common
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 mariadb-client-10.0 : Depends: libdbd-mysql-perl (>= 1.2202) but it is not going to be installed
 mariadb-client-core-10.0 : Depends: mariadb-common (>= 10.0.36-0ubuntu0.16.04.1) but it is not going to be installed
E: Error, pkgProblemResolver::Resolve generated breaks, this may be caused by held packages.
ubuntu@ip-172-31-45-140:~$ sudo apt-get autoremove
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be REMOVED:
  libdbd-mysql-perl libdbi-perl libmysqlclient20 libterm-readkey-perl mariadb-common
0 upgraded, 0 newly installed, 5 to remove and 23 not upgraded.
2 not fully installed or removed.
After this operation, 6,931 kB disk space will be freed.
Do you want to continue? [Y/n] y
(Reading database ... 93704 files and directories currently installed.)
Removing libdbd-mysql-perl (4.033-1ubuntu0.1) ...
Removing libdbi-perl (1.634-1build1) ...
Removing libmysqlclient20:amd64 (5.7.23-0ubuntu0.16.04.1) ...
Removing libterm-readkey-perl (2.33-1build1) ...
Removing mariadb-common (10.0.36-0ubuntu0.16.04.1) ...
Processing triggers for man-db (2.7.5-1) ...
Processing triggers for libc-bin (2.23-0ubuntu10) ...
Setting up mysql-server-5.7 (5.7.23-0ubuntu0.16.04.1) ...
Renaming removed key_buffer and myisam-recover options (if present)
ERROR: Unable to start MySQL server:
mysqld: Can't read dir of '/etc/mysql/conf.d/' (Errcode: 2 - No such file or directory)
mysqld: [ERROR] Fatal error in defaults handling. Program aborted!
Please take a look at https://wiki.debian.org/Teams/MySQL/FAQ for tips on fixing common upgrade issues.
Once the problem is resolved, run apt-get --fix-broken install to retry.
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
No apport report written because the error message indicates its a followup error from a previous failure.
                                                                                                          Errors were encountered while processing:
 mysql-server-5.7
 mysql-server
E: Sub-process /usr/bin/dpkg returned an error code (1)
ubuntu@ip-172-31-45-140:~$ sudo apt-get autoclean
Reading package lists... Done
Building dependency tree
Reading state information... Done
ubuntu@ip-172-31-45-140:~$ sudo apt-get install mariadb-server
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following package was automatically installed and is no longer required:
  libevent-core-2.0-5
Use 'sudo apt autoremove' to remove it.
The following additional packages will be installed:
  libdbd-mysql-perl libdbi-perl libmysqlclient20 libterm-readkey-perl mariadb-client-10.0 mariadb-client-core-10.0 mariadb-common mariadb-server-10.0 mariadb-server-core-10.0
Suggested packages:
  libclone-perl libmldbm-perl libnet-daemon-perl libsql-statement-perl mailx mariadb-test tinyca
The following packages will be REMOVED:
  mysql-client mysql-client-5.7 mysql-client-core-5.7 mysql-server mysql-server-5.7 mysql-server-core-5.7
The following NEW packages will be installed:
  libdbd-mysql-perl libdbi-perl libmysqlclient20 libterm-readkey-perl mariadb-client-10.0 mariadb-client-core-10.0 mariadb-common mariadb-server mariadb-server-10.0 mariadb-server-core-10.0
0 upgraded, 10 newly installed, 6 to remove and 23 not upgraded.
2 not fully installed or removed.
Need to get 16.8 MB of archives.
After this operation, 15.4 MB disk space will be freed.
Do you want to continue? [Y/n] y
Get:1 http://eu-central-1.ec2.archive.ubuntu.com/ubuntu xenial-updates/universe amd64 mariadb-client-10.0 amd64 10.0.36-0ubuntu0.16.04.1 [1,161 kB]
Get:2 http://eu-central-1.ec2.archive.ubuntu.com/ubuntu xenial/main amd64 libdbi-perl amd64 1.634-1build1 [743 kB]
Get:3 http://eu-central-1.ec2.archive.ubuntu.com/ubuntu xenial-updates/main amd64 libmysqlclient20 amd64 5.7.23-0ubuntu0.16.04.1 [812 kB]
Get:4 http://eu-central-1.ec2.archive.ubuntu.com/ubuntu xenial-updates/universe amd64 libdbd-mysql-perl amd64 4.033-1ubuntu0.1 [84.3 kB]
Get:5 http://eu-central-1.ec2.archive.ubuntu.com/ubuntu xenial/universe amd64 libterm-readkey-perl amd64 2.33-1build1 [27.2 kB]
Get:6 http://eu-central-1.ec2.archive.ubuntu.com/ubuntu xenial-updates/universe amd64 mariadb-common all 10.0.36-0ubuntu0.16.04.1 [16.0 kB]
Get:7 http://eu-central-1.ec2.archive.ubuntu.com/ubuntu xenial-updates/universe amd64 mariadb-client-core-10.0 amd64 10.0.36-0ubuntu0.16.04.1 [4,640 kB]
Get:8 http://eu-central-1.ec2.archive.ubuntu.com/ubuntu xenial-updates/universe amd64 mariadb-server-core-10.0 amd64 10.0.36-0ubuntu0.16.04.1 [4,858 kB]
Get:9 http://eu-central-1.ec2.archive.ubuntu.com/ubuntu xenial-updates/universe amd64 mariadb-server-10.0 amd64 10.0.36-0ubuntu0.16.04.1 [4,418 kB]
Get:10 http://eu-central-1.ec2.archive.ubuntu.com/ubuntu xenial-updates/universe amd64 mariadb-server all 10.0.36-0ubuntu0.16.04.1 [13.1 kB]
Fetched 16.8 MB in 0s (41.3 MB/s)
Preconfiguring packages ...
(Reading database ... 93502 files and directories currently installed.)
Removing mysql-server (5.7.23-0ubuntu0.16.04.1) ...
Removing mysql-server-5.7 (5.7.23-0ubuntu0.16.04.1) ...
Removing mysql-server-core-5.7 (5.7.23-0ubuntu0.16.04.1) ...
Removing mysql-client (5.7.23-0ubuntu0.16.04.1) ...
dpkg: mysql-client-5.7: dependency problems, but removing anyway as you requested:
 dbconfig-mysql depends on mysql-client | mariadb-client | virtual-mysql-client; however:
  Package mysql-client is not installed.
  Package mariadb-client is not installed.
  Package virtual-mysql-client is not installed.
  Package mysql-client-5.7 which provides virtual-mysql-client is to be removed.
  Package mariadb-client-10.0 which provides virtual-mysql-client is not installed.

Removing mysql-client-5.7 (5.7.23-0ubuntu0.16.04.1) ...
Removing mysql-client-core-5.7 (5.7.23-0ubuntu0.16.04.1) ...
Processing triggers for man-db (2.7.5-1) ...
Selecting previously unselected package mariadb-client-10.0.
(Reading database ... 93277 files and directories currently installed.)
Preparing to unpack .../mariadb-client-10.0_10.0.36-0ubuntu0.16.04.1_amd64.deb ...
Unpacking mariadb-client-10.0 (10.0.36-0ubuntu0.16.04.1) ...
Selecting previously unselected package libdbi-perl.
Preparing to unpack .../libdbi-perl_1.634-1build1_amd64.deb ...
Unpacking libdbi-perl (1.634-1build1) ...
Selecting previously unselected package libmysqlclient20:amd64.
Preparing to unpack .../libmysqlclient20_5.7.23-0ubuntu0.16.04.1_amd64.deb ...
Unpacking libmysqlclient20:amd64 (5.7.23-0ubuntu0.16.04.1) ...
Selecting previously unselected package libdbd-mysql-perl.
Preparing to unpack .../libdbd-mysql-perl_4.033-1ubuntu0.1_amd64.deb ...
Unpacking libdbd-mysql-perl (4.033-1ubuntu0.1) ...
Selecting previously unselected package libterm-readkey-perl.
Preparing to unpack .../libterm-readkey-perl_2.33-1build1_amd64.deb ...
Unpacking libterm-readkey-perl (2.33-1build1) ...
Selecting previously unselected package mariadb-common.
Preparing to unpack .../mariadb-common_10.0.36-0ubuntu0.16.04.1_all.deb ...
Unpacking mariadb-common (10.0.36-0ubuntu0.16.04.1) ...
Selecting previously unselected package mariadb-client-core-10.0.
Preparing to unpack .../mariadb-client-core-10.0_10.0.36-0ubuntu0.16.04.1_amd64.deb ...
Unpacking mariadb-client-core-10.0 (10.0.36-0ubuntu0.16.04.1) ...
Selecting previously unselected package mariadb-server-core-10.0.
Preparing to unpack .../mariadb-server-core-10.0_10.0.36-0ubuntu0.16.04.1_amd64.deb ...
Unpacking mariadb-server-core-10.0 (10.0.36-0ubuntu0.16.04.1) ...
Processing triggers for man-db (2.7.5-1) ...
Processing triggers for libc-bin (2.23-0ubuntu10) ...
Setting up mariadb-common (10.0.36-0ubuntu0.16.04.1) ...
update-alternatives: error: alternative path /etc/mysql/mariadb.cnf doesn't exist
dpkg: error processing package mariadb-common (--configure):
 subprocess installed post-installation script returned error exit status 2
E: Sub-process /usr/bin/dpkg returned an error code (1)
ubuntu@ip-172-31-45-140:~$