# MySQL

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

Note: MariaDB is now officially Arch Linux's default implementation of MySQL. It is recommended for all users to upgrade to MariaDB. Oracle MySQL was dropped to the AUR. See the announcement.

## 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

- Percona Server — An implementation by Percona LLC.

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

Tip: If the database (in `/var/lib/mysql`) resides in a btrfs file system you should consider disabling Copy-on-Write for the directory before creating any database:

`# chattr +C /var/lib/mysql`

Start `mysqld.service`, and then run the setup script:

    # mysql_secure_installation

and restart `mysqld.service` afterwards.

Front-ends available are mysql-gui-tools and its successor mysql-workbench.

### Enable at startup

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

### Upgrade from Oracle MySQL to MariaDB

Note: It could be needed to remove the following files from `/var/lib/mysql` : `ib_logfile0`, `ib_logfile1` and `aria_log_control` before restarting the daemon in the following procedure.

Users who want to switch will need to stop `mysqld.service`, install mariadb, start `mysqld.service`, and 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

### Grant Remote Access

If you want to access your MySQL server from other LAN hosts, you have to comment out (with #) the following lines in your `/etc/mysql/my.cnf`:

    [mysqld]
       ...
       #skip-networking
       #bind-address = <some ip-address>
       ...

Then you grant any mysql user you like remote access from your local network (example for root): Connect to your database with root:

    mysql -p -u root

Check current users with remote access privileged:

    SELECT User, Host FROM mysql.user WHERE Host <> 'localhost';

Now grant remote access for your user (here root)::

    GRANT ALL PRIVILEGES ON *.* TO 'root'@'192.168.1.%' IDENTIFIED BY 'my_optional_remote_password' WITH GRANT OPTION;

You can change the '%' wildcard to a specific host if you like. The password can be different from user's main password.

### 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

Note: Enabling this feature can make the client initialization longer.

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 ).

### Time zone tables

Although time zone tables are created during the installation, they are not automatically populated. They need to be populated if you are planning on using CONVERT_TZ() in SQL queries.

To populate the time zone tables with all the time zones:

    $ mysql_tzinfo_to_sql /usr/share/zoneinfo | mysql -u root mysql

Optionally, you may populate the table with specific time zone files:

    $ mysql_tzinfo_to_sql <timezone_file> <timezone_name> | mysql -u root 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 `mysqld.service`. 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:

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

Start `mysqld.service`.

### 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

### Cannot login through CLI, but phpmyadmin works well

This may happen if you're using a long (>70-75) password. As for 5.5.36, for some reason, mysql CLI cannot handle that much characters in readline mode. So, if you're planning to use the recommended password input mode:

    $ mysql -u <user> -p
    Password:

consider changing the password to smaller one.

Note: You still can log in by specifying the password an an argument to mysql command.
Warning: This behavior considered dangerous, because your password might leak, for example, to the logs. Use it only in case of emergency and don't forget to change password right afterwards.

    $ mysql -u <user> -p"<some-veryveryveryveryveryveryveryveryveryveryveryveryveryveryvery-long-and-veryveryveryveryveryveryveryveryveryvery-strong-password>"

## 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

Category:

- Database management systems