RHEL7单独安装图形X11

RHEL7 默认是最小化安装（Minimal Install），没有图形界面，
我们应该选择Server with GUI。若已错过此步骤，我们采用以下方式补充安装GUI界面。

# yum group list

Available Environment Groups:
   Minimal Install
   Compute Node
   Infrastructure Server
   File and Print Server
   Basic Web Server
   Virtualization Host
   Server with GUI
   GNOME Desktop
   KDE Plasma Workspaces
   Development and Creative Workstation
Available Groups:
   Compatibility Libraries
   Console Internet Tools
   Development Tools
   Graphical Administration Tools
   Legacy UNIX Compatibility
   Scientific Support
   Security Tools
   Smart Card Support
   System Administration Tools
   System Management

# yum -y groupinstall "Server with GUI"

启动X11图形界面

# startx

修改默认运行级别/目标

# ln -sf /lib/systemd/system/multi-user.target /etc/systemd/system/default.target   //图形模式
# ln -sf /lib/systemd/system/graphical.target /etc/systemd/system/default.target   //图形模式

使用systemctl来切换

# systemctl -f enable multi-user.target   //文字模式
# systemctl -f enable graphical.target   //图形模式