Before we get into how to do this; the Spigot snapshot release is not stable and should NOT be used in production environment servers. A lot of plugins still need to be updated to support 1.18, so expect bugs, and expect issues. DedicatedMC is not responsible for any sort of damage to worlds as a result of updating ahead of a stable release.
Before you update to a snapshot release, make sure to run the --forceUpgrade command in your server startup arguments. In this guide, we will be using the DedicatedMC Raw Power Panel.
It should promptly upgrade all existing chunks in your current worlds. Allow it to finish, and your server to fully boot. Once it fully boots, turn it back off.
Upload the compiled Spigot jar in the main server directory. Click "Upload" in the top right of your Raw Power Panel and select the spigot jar in your local system.
Change the name in "Startup Settings" to the name of your spigot jar.
Run another pass of --forceUpgrade and allow it to finish and your server to fully boot. Turn your server off after it finishes startup completely.
Disable the --forceUpgrade command by either removing the argument or changing the 1 to a 0 from the DedicatedMC Raw Power Panel.
Start your server back up and look for any errors and report them promptly to the Spigot bug tracker.
Enjoy 1.18 Pre-Release 5 and be on the lookout for Paper's release and full version of 1.18!
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