@greda, I was able to figure a solution I’d sort of seen elsewhere to this exact issue, as I was having the same problem. Created an account to document the solution as this is the first thread that comes up when searching for a solution.

On a completely clean installation, and copy/pasting the terminal commands to install, I could get MM running just fine using pm2, but it would not auto-start. As it turns out, I missed a part of the auto-start instructions, and this caused the problem. Here’s my solution:

1. Look for the step “Starting PM2 on Boot”
2. Command is “pm2 startup”
3. There’s an instruction line there that’s easy to miss, which is this: "PM2 will now show you a command you need to execute."
4. IN THE TERMINAL, there is an output to the “pm2 startup” command when it’s done running saying that you need to copy and then re-paste to sent environmental variables
5. Copy/paste the output text from “pm2 startup” out of, then back into, Terminal
6. Proceed with the rest of the auto-start instructions as documented

This cleanly and easily solved the issue for me - it’s an easy step in the instructions to miss as it’s the only one where you need to do something with the output of the setup commands.