Difference between revisions of "MySQL"

Revision as of 13:30, 28 February 2014

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

Installation

The MySQL implementation chosen by Arch Linux is called MariaDB. Install mariadb from the official repositories. Alternative implementations are:

• Oracle MySQL — An implementation by Oracle Corporation.

https://www.mysql.com/ || mysql^AUR

• Percona Server — An implementation by Percona LLC.

http://www.percona.com/software/percona-server/ || percona-server

Start the mysqld daemon, run the setup script:

# mysql_secure_installation

and restart the daemon afterwards.

Front-ends available are mysql-gui-tools^AUR and mysql-workbench^AUR.

Enable at startup

To start the MySQL daemon at boot, enable mysqld systemd service.

Upgrade from Oracle MySQL to MariaDB

Users who want to switch will need to stop their current mysqld daemon, install mariadb, libmariadbclient or mariadb-clients, restart mysqldand execute:

# mysql_upgrade -p

in order to migrate their systems.

On update

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

# mysql_upgrade -u root -p

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

Disable remote access

The MySQL server is accessible from the network by default. If MySQL is only needed for the localhost, you can improve security by not listening on TCP port 3306. To refuse remote connections, uncomment the following line in /etc/mysql/my.cnf:

skip-networking

You will still be able to log in from the localhost.

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.

Using UTF-8

In the /etc/mysql/my.cnf file section under the mysqld group, add:

[mysqld]
init_connect                = 'SET collation_connection = utf8_general_ci,NAMES utf8'
collation_server            = utf8_general_ci
character_set_client        = utf8
character_set_server        = utf8

Using a TMPFS for tmpdir

The directory used by MySQL for storing temporary files is named tmpdir. For example, it is used to perform disk based large sorts, as well as for internal and explicit temporary tables.

Create the directory with appropriate permissions:

# mkdir -pv /var/lib/mysqltmp
# chown mysql:mysql /var/lib/mysqltmp

Find the id and gid of the mysql user and group:

$ id mysql
uid=27(mysql) gid=27(mysql) groups=27(mysql)

Add to your /etc/fstab file.

 tmpfs   /var/lib/mysqltmp   tmpfs   rw,gid=27,uid=27,size=100m,mode=0750,noatime   0 0

Add to your /etc/mysql/my.cnf file under the mysqld group:

 tmpdir      = /var/lib/mysqltmp

Then reboot or ( shutdown mysql, mount the tmpdir, start mysql ).

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 MySQL fails to start 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. Issue the following command:

# mysqld_safe --skip-grant-tables &

Connect to the mysql server. Issue the following command:

# 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.

Check and repair all tables

Check and auto repair all tables in all databases, see more:

# mysqlcheck -A --auto-repair -u root -p

Optimize all tables

Forcefully optimize all tables, automatically fixing table errors that may come up.

# mysqlcheck -A --auto-repair -f -o -u root -p

OS error 22 when running on ZFS

If you are using ZFS and get the following error:

InnoDB: Operating system error number 22 in a file operation.

You need to disable aio_writes by adding a line to the mysqld-section in /etc/mysql/my.cnf

[mysqld]
...
innodb_use_native_aio = 0

See also

• LAMP - ArchWiki article covering the setup of a LAMP server (Linux Apache MySQL PHP)
• PhpMyAdmin - ArchWiki article covering the web-based tool to help manage MySQL databases using an Apache/PHP front-end.
• PHP - ArchWiki article on PHP.
• MySQL Performance Tuning Scripts and Know-How