In the first installment I launched a basic Minecraft service on CentOS7. However, a proper service should not be run from the command line, instead it should be controlled by the system service daemon. In years past this would be by writing a ‘sysV init script’ which would try to determine if the process was running, if not launch it and capture its PID for future reference, and capture its output to a file. CentOS-7 has switched away from that model to one called SystemD which makes much of that easier. There is some controversy over the SystemD model (is it UNIX-y? Too monolithic? Taking over everything?) but seems pretty handy for what it needs to do, plus has some nice security features.
So I will create a Minecraft service definition for SystemD. I used http://0pointer.de/blog/projects/systemd-for-admins-3.html to help me with this. The unit file will look like:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
What this does:
- Defines the service name
- Designates that it requires the /minecraft mount and should run after the logging daemon starts.
- Provides the startup command, working directory, user/group
- Designates that /tmp should be private for that process
- Prevents the process from gaining any privileges.
- Hides /home from the process
- Makes most system directories read-only (to protect against accidental permissions issues)
- Makes /minecraft read-writeable.
The last few are for system protection — even if the java daemon is subverted to try to read the contents of /home, it can’t see it. Between the hidden and read-only directories, the limitation of privileges and the non-privileged launching user, there is much less chance of MineCraft causing system-wide havoc.
After putting the service defintion into place, reload systemd, restart the daemon and check its output:
1 2 3 4
To stop the service:
Output will be:
1 2 3 4 5 6 7 8 9 10 11 12
Update: firstname.lastname@example.org sent me a link to https://teilgedanken.de/Blog/post/8/ which takes this a step further and utilizes MCRCON to more gracefully control the servers shutdown state, and integrate with FirewallD if your system utilizes it.