How do I make a while true loop only start the program/minecraft server again if it closes or crashes?

Question

Hi I am running a Minecraft server with a restart plugin but it requires the program to restart itself, so I used a While true sleep 5 loop, and it seems to work fine but after some time it just starts opening again and again and there by it at some point gets to use 100% cpu usage all the time.

How do I make it not start the program again before the server closes or crashes?

#!/bin/sh
while true
do
java -Xms1G -Xmx6G -jar server.jar
sleep 5
done

Since sleep is set to 5 after it keeps opening again and again I see that is says failed to start the minecraft server every 5 secs but it is already running, and I want it to only run the while loop if the program is not running.

Answer 1

Using pgrep with the -f flag you can search for a running process with some arguments. You can use this to check if a server is already running.

For example:

#!/bin/bash

while true
do
    if ! pgrep -f server.jar
    then
        java -Xms1G -Xmx6G -jar server.jar
    fi
    sleep 5
done