I have a second MySQL 8 instance running on Ubunut 20.04, started by this command:
mysqld_safe --defaults-file=/home/user/mysqld_replica.cnf &
The config file contains all needed settings like port, socket and data dir. That works well but I can not figure out how to start the second instance on boot.
What would be the recommended way to start both instances at boot time?
Copy /lib/systemd/system/mysql.service to /etc/systemd/system/mysql_replica.service.
In the copied service file add --defaults-file=/home/user/mysqld_replica.cnf to the ExecStart* directives as the first argument to mysqld.
Reload systemd to read this systemctl daemon-reload.
Start the service systemctl start mysql_replica.service.
Enable on boot with systemctl enable mysql_replica.service.
You many need a few quick apparmor fixes like this answer to enable writing on your second data directory.
