If you’re unable to restart mysqld and troubleshooting the cause: if u log into SSH and go to /tmp you may see that there is no simlink

To create a simlink you can do the following:

cd /var/lib/mysql/
touch mysql.sock
chmod 1777 mysql.sock
chown mysql.mysql mysql.sock

Create a symlink for the sock file :-
ln -s /var/lib/mysql/mysql.sock /tmp

Restart mysql :- service mysql restart

Then your MySQL service should be back to normal.