# systemctl       #输出已激活单元

# systemctl list-units    #输出已激活单元

# systemctl --failed      #输出运行失败的单元

# systemctl list-unit-files   #查看所有已安装服务

# systemctl start nginx   #启动nginx

# systemctl stop nginx    #停止nginx

# systemctl restart nginx   #重启nginx

# systemctl reload nginx    #重新加载nginx配置

# systemctl status nginx    #输出nginx运行状态

# systemctl is-enabled nginx  #检查nginx是否配置为自动启动

# systemctl enable nginx    #开机自动启动nginx

# systemctl disable nginx   #取消开机自动启动nginx

# systemctl help nginx    #显示nginx的手册页

# systemctl daemon-reload   #重新载入 systemd，扫描新的或有变动的单元

# systemctl reboot      #重启

# systemctl poweroff      #退出系统并停止电源

# systemctl suspend     #待机

# systemctl hibernate   #休眠

# systemctl hybrid-sleep    #混合休眠模式（同时休眠到硬盘并待机

# systemctl isolate graphical.target  #等价于telinit 3 或 telinit 5