了解一下centos7的运行级别：

# ll /usr/lib/systemd/system/runlevel*target
lrwxrwxrwx. 1 root root 15 Nov 30 02:38 /usr/lib/systemd/system/runlevel0.target -> poweroff.target
lrwxrwxrwx. 1 root root 13 Nov 30 02:38 /usr/lib/systemd/system/runlevel1.target -> rescue.target
lrwxrwxrwx. 1 root root 17 Nov 30 02:38 /usr/lib/systemd/system/runlevel2.target -> multi-user.target
lrwxrwxrwx. 1 root root 17 Nov 30 02:38 /usr/lib/systemd/system/runlevel3.target -> multi-user.target
lrwxrwxrwx. 1 root root 17 Nov 30 02:38 /usr/lib/systemd/system/runlevel4.target -> multi-user.target
lrwxrwxrwx. 1 root root 16 Nov 30 02:38 /usr/lib/systemd/system/runlevel5.target -> graphical.target
lrwxrwxrwx. 1 root root 13 Nov 30 02:38 /usr/lib/systemd/system/runlevel6.target -> reboot.target![]

这次使用的就是rescue target,救援模式

挂载好你的光驱或者U盘系统盘

使用光盘或者U盘引导

根据提示按回车，继续

根据提示，你的系统根目录是/mnt/sysimage

1712/01/dc531416a657f13275062f8304159ef8.png?x-oss-process=image/watermark,size_16,text_QDUxQ1RP5Y2a5a6i,color_FFFFFF,t_100,g_se,x_10,y_10,shadow_90,type_ZmFuZ3poZW5naGVpdGk=)

exit

reboot

救援模式能做的事情很多