Joomla can't find file jos_session.frm or MySQL Can't read dir (errno: 13)

If you find an Error message containing one of

1. "Can't find file" ... "jos_session.frm"
2. MySQL Can't read dir ... (errno: 13)

This is easily Due to:

1. Incorrect MySQL Directory Ownership
2. MySQL server Started by Wrong User

To correct this first you need to determine what user is running the MySQL Server by:

ps aux | grep mysql

If you receive a line of output containing the directory where your MySQL process
is Resident you can proceed to change the Ownership.
First select the MySQL Path but "/bin/mysqld", copy it and then paste in this:
Example:

sudo chown -R mysql:mysql yourMySQLBasePathDir

If your path contains also the MySQL version number you should have also a symbolic link from this one to a "mysql" dir and you will need to change ownerships also to this second one.

After you should check you are able to login as mysql user by:

su mysql

If you haven't already set a password you should provide to set it by:

sudo passwd mysql

Now as mysql user you can stop and restart the mysql server:

sudo killall mysqld

yourMySQLBasePathDir/bin/mysqld_safe