verup_to_latest.sh

#!/bin/bash

set -eu

yum install -y jq

readonly MINECRAFT_DIR="/opt/minecraft_server"
readonly BACKUP_DIR_PREFIX="backup"
readonly MINECRAFT_SERVER_SERVICE="/etc/systemd/system/minecraft-server.service"

readonly MINECRAFT_SERVER_LATEST_VER=$( curl https://launchermeta.mojang.com/mc/game/version_manifest.json|jq -r '."latest"."release"' )
readonly MINECRAFT_SERVER_LATEST_MANIFEST_URL=$( curl https://launchermeta.mojang.com/mc/game/version_manifest.json | jq -r ".\"versions\"[] | select (.\"id\"==\"${MINECRAFT_SERVER_LATEST_VER}\") | .\"url\" " )
readonly MINECRAFT_SERVER_LATEST_JAR_URL=$( curl "${MINECRAFT_SERVER_LATEST_MANIFEST_URL}" | jq -r ".\"downloads\".\"server\".\"url\"" )
readonly MINECRAFT_SERVER_CURRENT_INSTALLED_VER=$( find /opt/minecraft_server -maxdepth 1 -name "*.jar" | cut -d '/' -f4 | sed -e "s/minecraft_server\.//" -e "s/\.jar//" )

readonly BACKUP_DIR="${MINECRAFT_SERVER_CURRENT_INSTALLED_VER}-$(date --iso-8601='minutes')"

function fullfill_requirements(){
    echo "Fullfill requirements"
    yum install -y screen

    groupadd minecraft || true
    useradd -g minecraft minecraft || true
}

function backup_installed_minecraft(){
    echo "Backup installed minecraft"
    mkdir -p "${MINECRAFT_DIR}/${BACKUP_DIR_PREFIX}/${BACKUP_DIR}"
    cp -r ${MINECRAFT_DIR}/[^backup]* "${MINECRAFT_DIR}/${BACKUP_DIR_PREFIX}/${BACKUP_DIR}"
    mv /etc/systemd/system/minecraft-server.service "${MINECRAFT_DIR}/${BACKUP_DIR_PREFIX}/${BACKUP_DIR}"
}

function install_latest_openjdk(){
    echo "Install latest openjdk"
    yum install -y java-latest-openjdk
    local latest_java_profile_number
    readonly latest_java_profile_number=$(echo '' | alternatives --config java | grep 'latest'|awk '{print $1}')
    echo "${latest_java_profile_number}" | alternatives --config java
}

function install_latest_minecraft_server(){
    echo "Install latest minecraft server: ${MINECRAFT_SERVER_LATEST_VER}"
    rm "${MINECRAFT_DIR}/minecraft_server.${MINECRAFT_SERVER_CURRENT_INSTALLED_VER}.jar"
    wget "${MINECRAFT_SERVER_LATEST_JAR_URL}" -O "${MINECRAFT_DIR}/minecraft_server.${MINECRAFT_SERVER_LATEST_VER}.jar"
    chown -R minecraft:minecraft ${MINECRAFT_DIR}
}

function generate_systemd_service(){
    local jvm_xmx_param
    readonly jvm_xmx_param=${1}

    echo "Generate newer systemd.service for Minecraft server"

    cat >> ${MINECRAFT_SERVER_SERVICE} <<EOF
[Unit]
Description=Minecraft Server
After=network.target

[Service]
WorkingDirectory=${MINECRAFT_DIR}
User=minecraft
Group=minecraft
ProtectSystem=full
ProtectHome=true

ExecStart=/bin/sh -c '/usr/bin/screen -DmS minecraft /usr/bin/java -server -Xms512M -Xmx${jvm_xmx_param} -XX:+UseG1GC -XX:ParallelGCThreads=2 -XX:MinHeapFreeRatio=5 -XX:MaxHeapFreeRatio=10 -jar ${MINECRAFT_DIR}/minecraft_server.${MINECRAFT_SERVER_LATEST_VER}.jar --forceUpgrade nogui'

ExecReload=/usr/bin/screen -p 0 -S minecraft -X eval 'stuff "reload"\\015'

ExecStop=/usr/bin/screen -p 0 -S minecraft -X eval 'stuff "say SERVER SHUTTING DOWN. Saving map..."\\015'
ExecStop=/usr/bin/screen -p 0 -S minecraft -X eval 'stuff "save-all"\\015'
ExecStop=/usr/bin/screen -p 0 -S minecraft -X eval 'stuff "stop"\\015'
ExecStop=/bin/sleep 5

Restart=on-failure
RestartSec=60s

[Install]
WantedBy=multi-user.target
EOF

    systemctl daemon-reload
}

function get_java_xmx_param(){
    for line in $(grep ExecStart ${MINECRAFT_SERVER_SERVICE});do
        if echo "${line}" | grep -q "\-Xmx"; then
            echo "${line}" | tr -d "\-Xmx"
        fi
    done
}

function main(){
    yum makecache
    systemctl disable --now  minecraft-server.service

    fullfill_requirements

    local jvm_xmx_param
    readonly jvm_xmx_param=$(get_java_xmx_param)

    backup_installed_minecraft

    local default_java_version
    readonly default_java_version=$(java -version |& grep version | awk '{print $3}' | tr -d '"')
    local query_java_180="1.8.0*"
    if [[ ${default_java_version} =~ ${query_java_180} ]];then
        install_latest_openjdk
    fi

    install_latest_minecraft_server

    generate_systemd_service "${jvm_xmx_param}"
    systemctl enable --now minecraft-server.service
}

main