2.5.9 Managing MySQL Server with systemd

systemd provides automatic MySQL server startup and shutdown. It also enables manual server management using the systemctl command. For example:

systemctl {start|stop|restart|status} mysqld

Alternatively, use the service command (with the arguments reversed), which is compatible with System V systems:

service mysqld {start|stop|restart|status}

Support for systemd includes these files:

To add or change systemd options for MySQL, these methods are available:

To use a localized systemd configuration file, create the /etc/systemd/system/mysqld.service.d directory if it does not exist. In that directory, create a file that contains a [Service] section listing the desired settings. For example:

[Service]
LimitNOFILE=max_open_files
PIDFile=/path/to/pid/file
Nice=nice_level
LimitCore=core_file_limit
Environment="LD_PRELOAD=/path/to/malloc/library"
Environment="TZ=time_zone_setting"

The discussion here uses override.conf as the name of this file. Newer versions of systemd support the following command, which opens an editor and permits you to edit the file:

systemctl edit mysqld  # RPM platforms
systemctl edit mysql   # Debian platforms

Whenever you create or change override.conf, reload the systemd configuration, then tell systemd to restart the MySQL service:

systemctl daemon-reload
systemctl restart mysqld  # RPM platforms
systemctl restart mysql   # Debian platforms

With systemd, the override.conf configuration method must be used for certain parameters, rather than settings in a [mysqld] or [mysqld_safe] group in a MySQL option file:

For additional information about using systemd rather than mysqld_safe, see Migrating from mysqld_safe to systemd.

You can set the following parameters in override.conf:

Some MySQL parameters are configured using environment variables:

There are multiple ways to specify environment variable values for use by the MySQL server process managed by systemd:

To specify options for mysqld without modifying systemd configuration files directly, set or unset the MYSQLD_OPTS systemd variable. For example:

systemctl set-environment MYSQLD_OPTS="--general_log=1"
systemctl unset-environment MYSQLD_OPTS

MYSQLD_OPTS can also be set in the /etc/sysconfig/mysql file.

After modifying the systemd environment, restart the server to make the changes effective:

systemctl restart mysqld  # RPM platforms
systemctl restart mysql   # Debian platforms

For platforms that use systemd, the data directory is initialized if empty at server startup. This might be a problem if the data directory is a remote mount that has temporarily disappeared: The mount point would appear to be an empty data directory, which then would be initialized as a new data directory. To suppress this automatic initialization behavior, specify the following line in the /etc/sysconfig/mysql file (create the file if it does not exist):

NO_INIT=true

This section describes how to configure systemd for multiple instances of MySQL.

To use multiple-instance capability, modify the my.cnf option file to include configuration of key options for each instance. These file locations are typical:

For example, to manage two instances named replica01 and replica02, add something like this to the option file:

RPM platforms:

[mysqld@replica01]
datadir=/var/lib/mysql-replica01
socket=/var/lib/mysql-replica01/mysql.sock
port=3307
log-error=/var/log/mysqld-replica01.log

[mysqld@replica02]
datadir=/var/lib/mysql-replica02
socket=/var/lib/mysql-replica02/mysql.sock
port=3308
log-error=/var/log/mysqld-replica02.log

Debian platforms:

[mysqld@replica01]
datadir=/var/lib/mysql-replica01
socket=/var/lib/mysql-replica01/mysql.sock
port=3307
log-error=/var/log/mysql/replica01.log

[mysqld@replica02]
datadir=/var/lib/mysql-replica02
socket=/var/lib/mysql-replica02/mysql.sock
port=3308
log-error=/var/log/mysql/replica02.log

The replica names shown here use @ as the delimiter because that is the only delimiter supported by systemd.

Instances then are managed by normal systemd commands, such as:

systemctl start mysqld@replica01
systemctl start mysqld@replica02

To enable instances to run at boot time, do this:

systemctl enable mysqld@replica01
systemctl enable mysqld@replica02

Use of wildcards is also supported. For example, this command displays the status of all replica instances:

systemctl status 'mysqld@replica*'

For management of multiple MySQL instances on the same machine, systemd automatically uses a different unit file:

In the unit file, %I and %i reference the parameter passed in after the @ marker and are used to manage the specific instance. For a command such as this:

systemctl start mysqld@replica01

systemd starts the server using a command such as this:

mysqld --defaults-group-suffix=@%I ...

The result is that the [server], [mysqld], and [mysqld@replica01] option groups are read and used for that instance of the service.

Because mysqld_safe is not installed on platforms that use systemd to manage MySQL, options previously specified for that program (for example, in an [mysqld_safe] option group) must be specified another way: