Overview
MariaDB is a community-developed fork of MySQL, created by its original authors and designed as a drop-in replacement: same wire protocol, same default port 3306, and a largely compatible SQL dialect. It ships the mariadb client (with mysql kept as a compatibility symlink), making it the native choice on distributions like Arch and Fedora.
Relationship to MySQL
For most applications, MariaDB and MySQL are interchangeable. MariaDB renamed its tools with a mariadb- prefix (mariadb, mariadbd, mariadb-admin, mariadb-dump, mariadb-secure-installation) while keeping the classic mysql* names as symlinks. Pick one engine per host — the two cannot share port 3306.
Command-line tools
The suite includes mariadb (interactive client), mariadb-admin (administration), mariadb-dump (logical backups), and mariadb-secure-installation (hardening: set the root password, remove anonymous accounts and the test database).