Here is an error that can fall on you without crying guard:
Can not connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock'
From one moment to another moment, the database disappears for no apparent reason. This can be due to InnoDB which has to check that the tables are not broken and that has to then close MySQL.
You can verify the cause of the error by going to:
var / log / mysql / error.log
The problem can be solved with a simple:
Service mysql restart
If this does not work, you can try to kill the last mysql process:
Ps ax | Grep mysqld
kill -9 PID
Where PID is the first number from the left.
Otherwise, it may be necessary to reinstall the mysql server (not the mysql client):
apt-get install mysql-server
Or check the path to mysql: