centos: Another MySQL daemon already running with the same unix socket

To prevent the problem from occurring, you must perform a graceful shutdown of the server from the command line rather than powering off the server.

# shutdown -h now

This will stop the running services before powering down the machine.

Based on Centos, an additional method for getting it back up again when you run into this problem is to move mysql.sock:

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

# service mysqld start

Restarting the service creates a new entry called mqsql.sock

TL;DR:

Run this as root and you'll be all set:

rm $(grep socket /etc/my.cnf | cut -d= -f2)  && service mysqld start

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Longer version:

You can find the location of MySQL's socket file by manually poking around in /etc/my.conf, or just by using

grep socket /etc/my.cnf | cut -d= -f2

It is likely to be /var/lib/mysql/mysql.sock. Then (as root, of course, or with sudo prepended) remove that file:

rm /var/lib/mysql/mysql.sock

Then start the MySQL daemon:

service mysqld start

Removing mysqld will not address the problem at all. The problem is that CentOS & RedHat do not clean up the sock file after a crash, so you have to do it yourself. Avoiding powering off your system is (of course) also advised, but sometimes you can't avoid it, so this procedure will solve the problem.