将Java应用部署为Linux服务：理解内核与用户空间

[Unit]
Description=Hello Service -- A Sample Java Application Service
# 定义服务启动前的依赖关系，例如等待网络就绪
# After=network.target

[Service]
# 定义运行服务的用户和用户组，以限制权限
User=your_user
Group=your_group
# 指定服务的启动命令脚本
ExecStart=/path/to/start.sh
# (可选) 指定服务的停止命令脚本
ExecStop=/path/to/stop.sh
# 服务类型：forking表示ExecStart会启动一个父进程，然后父进程退出，子进程继续运行
Type=forking
# (可选) 设置工作目录
# WorkingDirectory=/path/to/your/app

[Install]
# 定义服务在哪些目标下被启用，default.target通常指多用户图形界面或命令行模式
WantedBy=default.target

#!/bin/bash

# 设置Java应用程序的类路径，包括JAR文件或目录
# /opt/hello 是应用根目录
# /opt/hello/* 是指应用根目录下的所有JAR文件
CLASSPATH="/opt/hello:/opt/hello/*"

# Java主类
MAIN_CLASS="com.package.hello.Start"

# 输出日志文件路径
LOG_FILE="/tmp/hello.out"

# 使用nohup启动Java应用，并将其标准输出和错误重定向到日志文件
# & 符号使其在后台运行
nohup java -cp "${CLASSPATH}" "${MAIN_CLASS}" > "${LOG_FILE}" 2>&1 &

# (可选) 记录进程ID，以便stop.sh脚本停止服务
echo $! > /tmp/hello.pid

#!/bin/bash

PID_FILE="/tmp/hello.pid"

if [ -f "${PID_FILE}" ]; then
    PID=$(cat "${PID_FILE}")
    if kill -0 "${PID}" 2>/dev/null; then # 检查进程是否存在
        echo "Stopping Java application with PID: ${PID}"
        kill "${PID}" # 尝试正常终止
        sleep 5 # 等待进程退出
        if kill -0 "${PID}" 2>/dev/null; then # 如果未退出，强制终止
            echo "Force stopping Java application with PID: ${PID}"
            kill -9 "${PID}"
        fi
        rm -f "${PID_FILE}"
    else
        echo "Java application not running or PID file stale."
        rm -f "${PID_FILE}"
    fi
else
    echo "PID file not found. Java application might not be running."
fi

# 重新加载systemd配置，使其识别新的服务文件
sudo systemctl daemon-reload

# 启用服务，使其在系统启动时自动运行
sudo systemctl enable hello-service.service

# 立即启动服务
sudo systemctl start hello-service.service

# 检查服务状态
sudo systemctl status hello-service.service

# 停止服务
sudo systemctl stop hello-service.service

# 重启服务
sudo systemctl restart hello-service.service

#!/bin/sh
### BEGIN INIT INFO
# Provides:          hello-service
# Required-Start:    $local_fs $network
# Required-Stop:     $local_fs
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: Start/stop Hello Java Service
### END INIT INFO

# 应用的安装路径
APP_HOME="/opt/hello"
# Java主类
MAIN_CLASS="com.package.hello.Start"
# JVM参数
JAVA_OPTS="-Xmx512m -Dlog4j.configurationFile=${APP_HOME}/config/log4j2.xml"
# 日志文件
LOG_FILE="/var/log/hello-service.log"
# PID文件
PID_FILE="/var/run/hello-service.pid"

start() {
    if [ -f "$PID_FILE" ] && kill -0 $(cat "$PID_FILE") 2>/dev/null; then
        echo "Service already running."
        return 1
    fi
    echo "Starting Hello Service..."
    nohup java -cp "${APP_HOME}:${APP_HOME}/*" ${JAVA_OPTS} "${MAIN_CLASS}" > "${LOG_FILE}" 2>&1 &
    echo $! > "$PID_FILE"
    echo "Service started."
}

stop() {
    if [ ! -f "$PID_FILE" ] || ! kill -0 $(cat "$PID_FILE") 2>/dev/null; then
        echo "Service not running."
        return 1
    fi
    echo "Stopping Hello Service..."
    kill $(cat "$PID_FILE")
    rm -f "$PID_FILE"
    echo "Service stopped."
}

case "$1" in
    start)
        start
        ;;
    stop)
        stop
        ;;
    restart)
        stop
        start
        ;;
    status)
        if [ -f "$PID_FILE" ] && kill -0 $(cat "$PID_FILE") 2>/dev/null; then
            echo "Service is running with PID $(cat "$PID_FILE")."
        else
            echo "Service is not running."
        fi
        ;;
    *)
        echo "Usage: $0 {start|stop|restart|status}"
        exit 1
        ;;
esac

exit 0

sudo chmod +x /etc/init.d/hello-service

# 对于基于Debian/Ubuntu的系统
sudo update-rc.d hello-service defaults

# 对于基于RedHat/CentOS的系统
# sudo chkconfig --add hello-service
# sudo chkconfig hello-service on