Check out example codes for "can't connect to local mysql server through socket '/var/run/mysqld/mysqld.sock'". It will help you in understanding the concepts better.

Code Example 1

# this saved my ass
# first  you must perform a graceful shutdown of the server from the command line rather than powering off the server
shutdown -h now

# an additional method for getting it back up again when you run into this problem is to move mysql.sock

# to centos
mv /var/lib/mysql/mysql.sock /var/lib/mysql/mysql.sock.bak

# to ubuntu
mv /var/run/mysqld/mysqld.sock /var/run/mysqld/mysqld.sock.bak

# restart mysql
service mysqld start

Code Example 2

sudo apt-get install mysql-server

Code Example 3

# Start your mysql server
/etc/init.d/mysql start

Code Example 4

> ln -s /var/lib/mysql/mysql.sock /tmp/mysql.sock
> 
> service mysql start or service mysql start

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