update-rc.d:tldr:6bdfb

The command "update-rc.d" is used in Linux systems to update the init script links. The init script links are responsible for starting and stopping services during the system startup process.

In this specific command, "${mysql}" is a placeholder for the name of the service. It should be replaced with the actual name of the MySQL service. For example, if the MySQL service is named "mysql-server", the command would be "update-rc.d mysql-server defaults".

The "defaults" parameter tells the "update-rc.d" command to set up the service to start and stop automatically during system startup and shutdown using the default runlevels defined in the system.

By running this command, you are configuring the system to start the specified service during boot time and stop it during system shutdown, following the default runlevel configuration.