(Note: To enable any command remove <!– at the start and –> at the end of the command lines. Disabled commands will be green in color, once enabled the color changes to black and red combination, for commands with — at the start just remove the —, for single line commands with // at the start remove the // to enable)

Here is how to fix when you get error /var/run/mysqld/mysqld.sock (2
Press CTRL+ALT+F1 and run below command:

mysqld_safe --skip-grant-tables &

Now press CTRL+ALT+F2 and run below commands:

mysql
mysql> use mysql
mysql> repair table host use_frm;
mysql> exit
service mysql restart

If MySQL is restarted without any error, you may reboot the system.
If MySQL still not working, follow the below steps:

nano /etc/mysql/mariadb.conf.d/50-server.cnf

Now add below line after the line, inndob_fast_shutdown = 0

innodb_force_recovery = 1

Save the file by pressing, CTRL+X, Y, Enter.
Run below command.

service mysql restart

If MySQL is restarted without any error, login to the POS system, take backup, reset system and restore the backup.
Now reboot the system and remove or comment the line ‘innodb_force_recovery = 1’ and reboot the system.