Linux系统如何用systemctl设置开机自启动服务？

# vi /etc/systemd/system/myapp.service
----------------------------------------------------
#如果/etc/systemd/system/myapp.service有过修改，需要进行更新，执行下面这个命令
#systemctl daemon-reload
#查看服务是否被正确识别
#systemctl list-unit-files|grep myapp
[Unit]
#服务描述，写有意义的内容，便于识别
Description=myapp service
[Service]
Type=simple
#设置应用的工作目录
WorkingDirectory=/myapp_path
ExecStart=/myapp_path/startMyApp.sh
ExecStop=/bin/kill -s TERM $MAINPID
[Install]
WantedBy=multi-user.target

# systemctl list-unit-files|grep myapp
--------------------------
myapp.service                      disabled

# vi /myapp_path/startMyApp.sh
----------------------------------------------------
#!/bin/sh
#上面这行很重要，会报203错误
#最好先cd到程序目录
cd /myapp_path
#使用java的绝对路径。如果找不到java可执行程序，也会报203错误
/usr/java/jdk1.8/bin/java -jar myapp.jar

# chmod +x myapp.sh

# systemctl start myapp.service

# systemctl stop myapp.service

# systemctl status myapp.service -l

# systemctl enable myapp.service
# systemctl list-unit-files|grep myapp
--------------------------
myapp.service                      enabled

# systemctl disable myapp.service
# systemctl list-unit-files|grep myapp
--------------------------
myapp.service                      disabled

# journalctl -flu myapp.service