1. list the default target that the system is configured to boot into.
[root@centos7 ~]# systemctl get-default multi-user.target
The multi-user.target is similar to the well known run level 3, which is essentially console only with networking enabled.
2. start the GUI
[root@centos7 ~]# systemctl isolate graphical.target
3. set the graphical target to become the default.
[root@centos7 ~]# systemctl set-default graphical.target Removed symlink /etc/systemd/system/default.target. Created symlink from /etc/systemd/system/default.target to /usr/lib/systemd/system/graphical.target.