If you're facing the problem do the following:
Run the CMD to check the dir/file is exists or not:
ls -l /var/run/mysqld/
If it doesn't exist, now, follow the above step.
Run the following command lines:
chown -R mysql:mysql /var/run/mysqld
service mysqld restart
It should solve the issue. If happens again than,
Create a new file /etc/tmpfiles.d/mysql.conf:
# systemd tmpfile settings for mysql
# See tmpfiles.d(5) for details
d /var/run/mysqld 0755 mysql mysql -
After reboot, MySQL should start normally.