stop (pause) inactive minecraft server process

minecraft-sleep.sh

#!/bin/bash
# /home/minecraft/bin/minecraft-sleep.sh

#set -v
cd "$(dirname "$0")"


# service name (i'm using systemd)
SERVICE_NAME="$1"

# set this to the port your minecraft server is on
#PORT=25565
PORT=`grep server-port ../$SERVICE_NAME/server.properties | cut -d '=' -f2`

# delay before starting
START_DELAY=600

# how frequently do we check for connections (seconds)
CHECK_DELAY=600

# script will start the server briefly duing each cycle
POLL_CYCLE=20

# how long to resume server during poll cycle
POLL_RUN=1

# delay in checking for connections during poll
POLL_DELAY=1

# maybe you want to customise this, eg if not using systemd
function find_pid(){
  echo $(ps -o 'pid,ppid,args,unit' `pgrep java` | grep $SERVICE_NAME | xargs | cut -d ' ' -f1)
}

function pause(){
 # this stops the process (like ctrl-z)
 PID=$(find_pid)
 if [ -n "$PID" ]; then
   kill -STOP $PID
 else
   echo "could not find PID"
 fi
}

function resume(){
 PID=$(find_pid)
 if [ -n "$PID" ]; then
   kill -CONT $PID
 else
   echo "could not find PID"
 fi
}



resume

sleep $START_DELAY

while true; do
 # wait a bit before looping again
 sleep 120

 # some random so processes don't wake up all at the same time
 sleep $[ ( $RANDOM % 10 )  + 1 ]s



 echo "checking for activity on $PORT"
# while ( netstat -tn | grep $PORT | grep ESTABLISHED ); do
 while ( netstat -tn | grep $PORT ); do
    #echo "still active..."
    sleep $CHECK_DELAY
 done
 
 echo "no active connections on $PORT, so pausing process $(find_pid)"
 pause

 echo "waiting for activity on $PORT, will run server for $POLL_RUN seconds every $POLL_CYCLE seconds."   
 ACTIVE=""
 while [ -z "$ACTIVE" ]; do
   #echo "Resume process $(find_pid) for $POLL_RUN seconds to prevent crashes/timeouts"
   resume
   sleep $POLL_RUN
   pause
   
   #echo "waiting for activity on $PORT"   
   POLL_UNTIL=$((SECONDS+POLL_CYCLE))
   while [ $SECONDS -lt $POLL_UNTIL ]; do 
     ACTIVE=`netstat -tn | grep $PORT`
     #echo "ACTIVE=$ACTIVE"
     if [ -n "$ACTIVE" ]; then 
        break
     else
        sleep $POLL_DELAY
     fi
   done
 done;

 echo "Resuming process $(find_pid) due to activty $ACTIVE"
 resume
 
 
done

minecraft-wake.sh

#!/bin/bash

# /home/minecraft/bin/minecraft-wake.sh

## this just pokes the port of a minecraft instance, making it wake up.  equivalent to `resume` in minecraft-sleep.sh
## you might want to use this if you have some scripts that run, eg backups, that need the server responding 
## as if a user was logged in

cd "$(dirname "$0")"
#set -v 

# service name (i'm using systemd)
SERVICE_NAME="$1"

# set this to the port your minecraft server is on
#PORT=25565
PORT=`grep server-port ../$SERVICE_NAME/server.properties | cut -d '=' -f2`

echo "boop" | nc -q 3 localhost $PORT

minecraft@.service

# /etc/systemd/system/minecraft@.service
# this is a systemd service, use start and/or enable (over reboots)
# presumes that minecraft runs as a restricted user 'minecraft'

[Unit]
Description=Minecraft Server: %i
After=network.target

[Service]
WorkingDirectory=/home/minecraft/%i

User=minecraft
Group=minecraft

Restart=always

ExecStartPre=/home/minecraft/bin/start-minecraft-sleep.sh %i 
ExecStart=/usr/bin/screen -DmS mc-%i /home/minecraft/%i/start.sh

ExecStop=/home/minecraft/bin/stop-minecraft-sleep.sh %i || true
ExecStop=/bin/sleep 3
ExecStop=/usr/bin/screen -p 0 -S mc-%i -X eval 'stuff "say SERVER SHUTTING DOWN IN 15 SECONDS..."\015' || true
ExecStop=/bin/sleep 5
ExecStop=/usr/bin/screen -p 0 -S mc-%i -X eval 'stuff "say SERVER SHUTTING DOWN IN 10 SECONDS..."\015' || true
ExecStop=/bin/sleep 5
ExecStop=/usr/bin/screen -p 0 -S mc-%i -X eval 'stuff "say SERVER SHUTTING DOWN IN 5 SECONDS..."\015' || true
ExecStop=/bin/sleep 5 
ExecStop=/usr/bin/screen -p 0 -S mc-%i -X eval 'stuff "save-all"\015' || true
ExecStop=/usr/bin/screen -p 0 -S mc-%i -X eval 'stuff "stop"\015' || true

[Install]
WantedBy=multi-user.target

start-minecraft-sleep.sh

#!/bin/bash
# /home/minecraft/bin/start-minecraft-sleep.sh

cd "$(dirname "$0")"

# the gawk is to add timestamps
./minecraft-sleep.sh $1 | gawk '{ print strftime("[%Y-%m-%d %H:%M:%S]"), $0 }' >> ../$1/logs/sleep.log &

stop-minecraft-sleep.sh

#!/bin/bash
# /home/minecraft/bin/stop-minecraft-sleep.sh

cd "$(dirname "$0")"
#set -v 

SERVICE_NAME=$1

# maybe you want to customise this, eg if not using systemd
function find_pid(){
  echo $(ps -o 'pid,ppid,args,unit' `pgrep java` | grep $SERVICE_NAME | cut -d ' ' -f1)
}

function resume(){
 PID=$(find_pid)
 if [ -n "$PID" ]; then
   kill -CONT $PID
 else
   echo "could not find PID"
 fi
}

echo "stopping minecraft-sleep.sh"
pkill -f "bin/minecraft-sleep.sh $1" || true
sleep 1
echo "resuming process $(find_pid)"
resume

glad it was of help. and i'm not sure this is my most elegant code - but is bash ever elegant!? :D

and indeed, adapt to fit. that is what i did based on michiel's code. i just had to generalise it a bit, since i am running three servers on the same box, and knockd seemed like overkill.

as an aside, i looked at this briefly too; https://github.com/jkutner/heroku-buildpack-minecraft - which is pretty clever (and free, but low RAM), but convoluted in how it exposes the port using ngrok. in the end, i hosted the minecraft servers on a pc at home, since 512mb isn't enough for a minecraft server unless you run an old version.