Check out example codes for "restart mysql". It will help you in understanding the concepts better.

Code Example 1

1. sudo /etc/init.d/mysql restart

 2. # service mysql restart

Code Example 2

sudo /etc/init.d/mysql start
or 
systemctl start mysql.service

Code Example 3

service mysql start
service mysql stop
service mysql restart

Code Example 4

sudo service mysql restart

Code Example 5

sudo /etc/init.d/mysql restart

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