MySQL - ArchWiki

# MySQL

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- phpMyAdmin
- Adminer
- JDBC and MySQL
- Open Database Connectivity

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

MariaDB is the default implementation of MySQL in Arch Linux, provided with the mariadb package.

Alternative implementations are:

- Oracle MySQL — An implementation by Oracle Corporation.

  https://www.mysql.com/ || mysqlAUR

- 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 on a Btrfs file system, you should consider disabling Copy-on-Write for the directory before creating any database.
- If the database resides on a ZFS file system, you should consult ZFS#Database before creating any database.

Install mariadb, afterwards run the following command before starting the `mariadb.service`:

    # mysql_install_db --user=mysql --basedir=/usr --datadir=/var/lib/mysql

Note: For security reasons, the systemd service file contains `ProtectHome=true`, which prevents MariaDB from accessing files under the `/home`, `/root` and `/run/user` hierarchies. The `datadir` has to be in an accessible location and owned by the `mysql` user and group. You can modify this behavior by creating a supplementary service file as described here: https://mariadb.com/kb/en/mariadb/systemd/

Now the `mariadb.service` can be started and/or enabled with systemd.

Tip: If you use something different from `/var/lib/mysql` for your data dir, you need to set `datadir=<YOUR_DATADIR>` under section `[mysqld]` of your `/etc/mysql/my.cnf`.

The following command will interactively guide you through a number of recommended security measures at the database level:

    # mysql_secure_installation

To simplify administration, you might want to install a front-end such as dbeaver, mysql-workbench, Adminer or phpMyAdmin. mysql-workbench is not completely compatible with MariaDB but can be used for basic tasks.

### Upgrade from Oracle MySQL to MariaDB

Note: It could be necessary 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.

See the announcement for the procedure to follow.

## Configuration

Once you have started the MySQL server and added a root account, you may want to change the default configuration.

To log in as `root` on the MySQL server, use the following command:

    $ mysql -u root -p

### Add user

Creating a new user takes two steps: create the user; grant privileges. In the below example, the user monty with some_pass as password is being created, then granted full permissions to the database mydb:

    $ mysql -u root -p

    MariaDB> CREATE USER 'monty'@'localhost' IDENTIFIED BY 'some_pass';
    MariaDB> GRANT ALL PRIVILEGES ON mydb.* TO 'monty'@'localhost';
    MariaDB> FLUSH PRIVILEGES;
    MariaDB> quit

### Configuration files

MariaDB configuration options are read from the following files in the given order (according to `mysqld --help --verbose` output):

    /etc/my.cnf /etc/mysql/my.cnf ~/.my.cnf

Depending on the scope of the changes you want to make (system-wide, user-only...), use the corresponding file. See this entry of the KnowledgeBase for more information.

### Grant remote access

Warning: This is not considered as best practice and may cause security issues. Consider using Secure Shell, VNC or VPN, if you want to maintain the MySQL-server outside and/or inside your LAN.

If you want to access your MySQL server from other LAN hosts, you have to edit the following lines in `/etc/mysql/my.cnf`:

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

Grant any MySQL user remote access (example for root):

    $ mysql -u root -p

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 UTF8MB4

Warning: Before changing the character set be sure to create a backup first.
Note: UTF8MB4 is recommended over UTF-8 since it allows full Unicode support [1] [2].

Append the following values to the main configuration file located at `/etc/mysql/my.cnf`:

    [client]
    default-character-set = utf8mb4

    [mysqld]
    collation_server = utf8mb4_unicode_ci
    character_set_server = utf8mb4

    [mysql]
    default-character-set = utf8mb4

Restart `mariadb.service` to apply the changes.

See #Database maintenance to optimize and check the database health.

### Increase character limit

Note: The character-limit depends on the character-set in use [3] [4] [5].

For InnoDB execute the following commands to support a higher character-limit:

    mysql> set global innodb_file_format = BARRACUDA;
    Query OK, 0 rows affected (0.00 sec)

    mysql> set global innodb_file_per_table = ON;
    Query OK, 0 rows affected (0.00 sec)

    mysql> set global innodb_large_prefix = ON;
    Query OK, 0 rows affected (0.00 sec)

Append the following lines in `/etc/mysql/my.cfg` to always use a higher character-limit:

    [mysqld]
    innodb_file_format = barracuda
    innodb_file_per_table = 1
    innodb_large_prefix = 1

Restart `mariadb.service` to apply the changes.

On table creating append the `ROW_FORMAT` as seen in the example:

    mysql> create table if not exists products (
       ->   day date not null,
       ->   product_id int not null,
       ->   dimension1 varchar(500) not null,
       ->   dimension2 varchar(500) not null,
       ->   unique index unique_index (day, product_id, dimension1, dimension2)
       -> ) ENGINE=InnoDB ROW_FORMAT=DYNAMIC;
    Query OK, 0 rows affected (0.02 sec)

### 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 -p mysql

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

    $ mysql_tzinfo_to_sql <timezone_file> <timezone_name> | mysql -u root -p mysql

## Database maintenance

### Upgrade databases on major releases

Upon a major version release of mariadb (for example mariadb-10.1.10-1 to mariadb-10.1.18-1), it is wise to upgrade databases:

    $ mysql_upgrade -u root -p

### Checking, optimizing and repairing databases

mariadb ships with `mysqlcheck` which can be used to check, repair, and optimize tables within databases from the shell. See the mysqlcheck man page for more. Several command tasks are shown:

To check all tables in all databases:

    $ mysqlcheck --all-databases -u root -p -c

To analyze all tables in all databases:

    $ mysqlcheck --all-databases -u root -p -a

To repair all tables in all databases:

    $ mysqlcheck --all-databases -u root -p -r

To optimize all tables in all databases:

    $ mysqlcheck --all-databases -u root -p -o

## Backup

There are various tools and strategies to back up your databases.

If you are using the default InnoDB storage engine, a suggested way of backing up all your bases online while provisioning for point-in-time recovery (also known as “roll-forward,” when you need to restore an old backup and replay the changes that happened since that backup) is to execute the following command:

    $ mysqldump --single-transaction --flush-logs --master-data=2 --all-databases -u root -p > all_databases.sql

This will prompt for MariaDB's root user's password, which was defined during database #Configuration.

Specifying the password on the command line is strongly discouraged, as it exposes it to discovery by other users through the use of `ps aux` or other techniques. Instead, the aforementioned command will prompt for the specified user's password, concealing it away.

### Compression

As SQL tables can get pretty large, it is recommended to pipe the output of the aforementioned command in a compression utility like gzip:

    $ mysqldump --single-transaction --flush-logs --master-data=2 --all-databases -u root -p | gzip > all_databases.sql.gz

Decompressing the backup thus created and reloading it in the server is achieved by doing:

    $ zcat all_databases.sql.gz | mysql -u root -p

This will recreate and repopulate all the databases previously backed up (see this or this).

### Non-interactive

If you want to setup non-interactive backup script for use in cron jobs or systemd timers, see option files and this illustration for mysqldump.

Basically you should add the following section to the relevant configuration file:

    [mysqldump]
    user=mysqluser
    password=secret

Mentioning a user here is optional, but doing so will free you from having to mention it on the command line.

#### Example script

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 and MariaDB manuals.

### Holland Backup

A python-based software package named Holland Backup is available in AUR to automate all of the backup work. It supports direct mysqldump, LVM snapshots to tar files (mysqllvm), LVM snapshots with mysqldump (mysqldump-lvm), and xtrabackup methods to extract the data. The Holland framework supports a multitude of options and is highly configurable to address almost any backup situation.

The main hollandAUR and holland-commonAUR packages provide the core framework; one of the sub-packages (holland-mysqldumpAUR, holland-mysqllvmAUR and/or holland-xtrabackupAUR must be installed for full operation. Example configurations for each method are in the `/usr/share/doc/holland/examples/` directory and can be copied to `/etc/holland/backupsets/`, as well as using the `holland mk-config` command to generate a base config for a named provider.

## Troubleshooting

### 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 `mariadb.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:

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

Start `mariadb.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

However, if the post install scripts failed because of the above issue, MySQL/MariaDB might be in an invalid state. To recover from this state, execute the following:

    rm -rf /var/lib/mysql/*
    mysql_install_db --user=mysql --basedir=/usr --datadir=/var/lib/mysql
    chown -R mysql:mysql /var/lib/mysql &>/dev/null
    /usr/bin/systemd-tmpfiles --create mysql.conf

After which MySQL/MariaDB should be installed correctly.

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

This may happen if you are 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 are 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 as an argument to mysql command.
Warning: This behavior is considered dangerous, because your password might leak, for example, to the logs. Use it only in case of emergency and do not forget to change password right afterwards.

    $ mysql -u <user> -p"<some-very-strong-password>"

### MySQL binary logs are taking up huge disk space

By default, mysqld creates binary log files in `/var/lib/mysql`. This is useful for replication master server or data recovery. But these binary logs can eat up your disk space. If you do not plan to use replication or data recovery features, you may disable binary logging by commenting out these lines in `/etc/mysql/my.cnf`:

    #log-bin=mysql-bin
    #binlog_format=mixed

Or you could limit the size of the logfile like this:

    expire_logs_days = 10
    max_binlog_size  = 100M

Alternatively, you can purge some binary logs in `/var/lib/mysql` to free up disk space with this command:

    # mysql -u root -p"PASSWORD" -e "PURGE BINARY LOGS TO 'mysql-bin.0000xx';"

### OpenRC fails to start MySQL

To use MySQL with OpenRC you need to add the following lines to the `[mysqld]` section in the MySQL config file, located at `/etc/mysql/my.cnf`.

    user = mysql
    basedir = /usr
    datadir = /var/lib/mysql
    pid-file = /run/mysqld/mysql.pid

You should now be able to start MySQL using:

    # rc-service mysql start

### Specified key was too long

See #Increase character limit.

## See also

- MariaDB Official Website
- MariaDB knowledge Base
- MySQL documentation
- Apache HTTP Server - ArchWiki article on the Apache HTTP Server
- PHP - ArchWiki article on PHP.
- MySQL Performance Tuning Scripts and Know-How

Category:

- Relational DBMSs