systemd

systemd is the default init system and service manager on modern Linux distributions (CentOS/RHEL 7+, Ubuntu 16.04+, Debian 8+). In the database context, it is the mechanism that starts, stops and monitors MySQL or MariaDB instances.

How it works #

Each service is defined by a unit file (e.g. mysqld.service) that specifies the startup command, configuration file, dependencies and crash behaviour. In a multi-instance setup, separate unit files are created for each instance (e.g. mysqld-app2.service, mysqld-reporting.service), each with its own --defaults-file pointing to a different my.cnf.

What it’s for #

systemd allows managing MySQL instances as independent services: starting, stopping, restarting and monitoring them separately. The systemctl cat <service> command is essential for tracing from the service name back to the instance’s configuration file, and from there to port, socket and datadir.

When to use it #

systemd is automatically active on any modern Linux server. In DBA work, you interact with it via systemctl start/stop/status/restart <service>. In multi-instance environments, systemctl list-units --type=service | grep mysql is the first command for identifying how many instances are running on a server.