Centos7下的默认启动方式和之前不同，查看 /etc/inittab 的内容，发现这里有备注更新：

inittab is no longer used when using systemd.

ADDING CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.
Ctrl-Alt-Delete is handled by /usr/lib/systemd/system/ctrl-alt-del.target

systemd uses 'targets' instead of runlevels. By default, there are two main targets:
multi-user.target: analogous to runlevel 3
graphical.target: analogous to runlevel 5

To view current default target, run:
systemctl get-default

To set a default target, run:
systemctl set-default TARGET.target

大意是使用targets取代了原来的runlevels。

获取当前默认启动的方式

systemctl get-default

默认启动图形界面

systemctl set-default graphical.target

设置成功后，会回显类似：

Removed symlink /etc/systemd/system/default.target.
Created symlink from /etc/systemd/system/default.target to /usr/lib/systemd/system/multi-user.target.

默认启动终端界面

systemctl set-default multi-user.target