MySQL

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MySQL is a widely spread, multi-threaded, multi-user SQL database. For more information about features, see the official homepage.

Installation

Install the mysql package from the official repositories.

After installing MySQL, start the mysqld daemon.

Run the setup script and restart the daemon afterwards:

# mysql_secure_installation
# systemctl restart mysqld

Configuration

Once you have started the MySQL server, you probably want to add a root account in order to maintain your MySQL users and databases. This can be done manually or automatically, as mentioned by the output of the above script. Either run the commands to set a password for the root account, or run the secure installation script.

You now should be able to do further configuration using your favorite interface. For example you can use MySQL's command line tool to log in as root into your MySQL server:

$ mysql -p -u root

Enable remote access

The MySQL server is not accessable from the network by default. To enable listing on TCP port 3306 to allow remote connections, comment out the following line in /etc/mysql/my.cnf:

skip-networking

Enable auto-completion

The MySQL client completion feature is disabled by default. To enable it system-wide edit /etc/mysql/my.cnf, and replace no-auto-rehash by auto-rehash. Completion will be enabled next time you run the MySQL client. Please note that enabling this feature can make the client initialization longer.

Upgrading

You might consider running this command after you have upgraded MySQL and started it:

# mysql_upgrade -u root -p

Backup

The database can be dumped to a file for easy backup. The following shell script will do this for you, creating a db_backup.gz file in the same directory as the script, containing your database dump:

#!/bin/bash

THISDIR=`dirname $(readlink -f "$0")`

mysqldump --single-transaction --flush-logs --master-data=2 --all-databases \
  | gzip > $THISDIR/db_backup.gz
echo 'purge master logs before date_sub(now(), interval 7 day);' | mysql

See also the official mysqldump page in the MySQL manual.

Troubleshooting

MySQL daemon cannot start

If you see something like this:

 :: Starting MySQL  [FAIL]

and there is no entry in the log files, you might want to check the permissions of files in the directories /var/lib/mysql and /var/lib/mysql/mysql. If the owner of files in these directories is not mysql:mysql, you should do the following:

 # chown mysql:mysql /var/lib/mysql -R

If you run into permission problems despite having followed the above, ensure that your my.cnf is copied to /etc/:

 # cp /etc/mysql/my.cnf /etc/my.cnf

Now try and start the daemon.

If you get these messages in your /var/lib/mysql/hostname.err

 [ERROR] Can't start server : Bind on unix socket: Permission denied
 [ERROR] Do you already have another mysqld server running on socket: /var/run/mysqld/mysqld.sock ?
 [ERROR] Aborting

The permissions of /var/run/mysqld could be the culprit.

 # chown mysql:mysql /var/run/mysqld -R

If you run mysqld and the following error appears:

 Fatal error: Can’t open and lock privilege tables: Table ‘mysql.host’ doesn’t exist

Run the following command from the /usr directory to install the default tables:

 # cd /usr
 # mysql_install_db --user=mysql --ldata=/var/lib/mysql/

Unable to run mysql_upgrade because MySQL cannot start

Try run MySQL in safemode:

# mysqld_safe --datadir=/var/lib/mysql/

And then run:

# mysql_upgrade -u root -p

Reset the root password

Stop the mysqld daemon.

# mysqld_safe --skip-grant-tables &

Connect to the mysql server

# mysql -u root mysql

Change root password:

 mysql> UPDATE mysql.user SET Password=PASSWORD('MyNewPass') WHERE User='root';
 mysql> FLUSH PRIVILEGES;
 mysql> exit

Start the mysqld daemon.

See also