Switch between text and graphical environments in Debian or RHEL

To switch between booting to a graphical environment and a console

Firstly run

systemctl get-default

which will show current setting, either

graphical.target

or

multi-user.target

To change, use 

systemctl set-default [graphical.target or multi-user.target]

To effect the change without rebooting, do

systemctl start [graphical.target or multi-user.target]

Of course in Slackware, we would simply edit Default Runlevel in /etc/inittab

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To install the GUI in RHEL

See also https://access.redhat.com/solutions/5238#res_a

Red Hat Enterprise Linux Server 8

yum group install GNOME base-x

or 

yum groupinstall Workstation

Red Hat Enterprise Linux Server 7

yum groupinstall gnome-desktop x11 fonts

For RHEL 7 Server you can target the "Server with GUI" group instead

yum groupinstall "Server with GUI"

Red Hat Enterprise Linux Server 6

yum groupinstall Desktop "General Purpose Desktop" "Desktop Platform" "X Window System"  "Internet Browser" "Graphical Administration Tools" Fonts

Minimal

yum groupinstall Desktop "X Window System" Fonts