ERROR 2002 (HY000): Can’t connect to local MySQL server

ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)

$ sudo apt-get remove --purge mysql-server* mysql-common

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:
 default-mysql-client : Depends: mysql-client-8.0 but it is not going to be installed
N: Ignoring file 'mariadb.list.old_1' in directory '/etc/apt/sources.list.d/' as it has an invalid filename extension
E: Error, pkgProblemResolver::Resolve generated breaks, this may be caused by held packages.

$ sudo rm /etc/apt/sources.list.d/mariadb.list.old_1

E: Error, pkgProblemResolver::Resolve generated breaks, this may be caused by held packages.

$ sudo dpkg --audit

The following packages are only half configured, probably due to problems
configuring them the first time.  The configuration should be retried using
dpkg --configure  or the configure menu option in dselect:
 phpmyadmin           MySQL web administration tool

$ sudo apt-get purge phpmyadmin

$ sudo dpkg --audit

$ sudo apt-get remove --purge mysql-server* mysql-common
$ sudo apt-get autoremove --purge
$ sudo rm -r /etc/mysql
$ sudo rm -r /var/lib/mysql

$ sudo apt purge mariadb-server
$ sudo apt autoremove
$ sudo apt clean

$ dpkg -l | grep mysql

$ dpkg -l | grep mariadb

$ sudo apt update
$ sudo apt install mariadb-server mariadb-client

Warning: The unit file, source configuration file or drop-ins of mariadb.service changed on disk. Run 'systemctl daemon-reload' to reload units.

$ sudo systemctl daemon-reload

$ sudo apt install mariadb-server mariadb-client

$ mysql --version

mysql Ver 15.1 Distrib 10.5.16-MariaDB, for debian-linux-gnu (x86_64) using readline 5.2

$ sudo mysql_secure_installation

NOTE: RUNNING ALL PARTS OF THIS SCRIPT IS RECOMMENDED FOR ALL MariaDB
      SERVERS IN PRODUCTION USE!  PLEASE READ EACH STEP CAREFULLY!

In order to log into MariaDB to secure it, we'll need the current
password for the root user. If you've just installed MariaDB, and
haven't set the root password yet, you should just press enter here.

Enter current password for root (enter for none):

OK, successfully used password, moving on...

Setting the root password or using the unix_socket ensures that nobody
can log into the MariaDB root user without the proper authorisation.

You already have your root account protected, so you can safely answer 'n'.

Switch to unix_socket authentication [Y/n] N

Change the root password? [Y/n] y

By default, a MariaDB installation has an anonymous user, allowing anyone
to log into MariaDB without having to have a user account created for
them.  This is intended only for testing, and to make the installation
go a bit smoother.  You should remove them before moving into a
production environment.

Remove anonymous users? [Y/n] Y

Normally, root should only be allowed to connect from 'localhost'.  This
ensures that someone cannot guess at the root password from the network.

Disallow root login remotely? [Y/n] Y

By default, MariaDB comes with a database named 'test' that anyone can
access.  This is also intended only for testing, and should be removed
before moving into a production environment.

Remove test database and access to it? [Y/n] Y

Reloading the privilege tables will ensure that all changes made so far
will take effect immediately.

Reload privilege tables now? [Y/n] Y

 ... 成功!

後片付け中...

すべて完了です!  上記の手順がすべて完了したなら、MariaDB
のインストールは安全になっているはずです。

MariaDBを使用していただきありがとうございます。

$ mysql -u root -p

MariaDB> CREATE USER '[追加ユーザーID]'@'[ホスト名 or IPアドレス]' IDENTIFIED BY '[パスワード]';
MariaDB> GRANT ALL PRIVILEGES ON [スキーマ名].* TO '[追加したユーザーID]'@'[接続元ホスト名やIPアドレス]';
MariaDB> FLUSH PRIVILEGES;
MariaDB> quit;

MariaDB> CREATE USER '[追加ユーザーID]'@'%' IDENTIFIED BY '[パスワード]';

MariaDB> GRANT ALL PRIVILEGES ON *.* TO '[追加ユーザーID]'@'[ホスト名 or IPアドレス]';

MariaDB> DROP USER '[追加ユーザーID]'@'[ホスト名 or IPアドレス]';

MariaDB> FLUSH PRIVILEGES;
MariaDB> quit;

MariaDB> SELECT user,host FROM mysql.user;

$ mysql -u [ユーザーID] -p