systemctl status default.target
# to switch runlevels instantly
systemctl isolate graphical.target
systemctl isolate multi-user.target
ll /etc/systemd/system/default.target
#runlevel 3
ln -sf /lib/systemd/system/multi-user.target /etc/systemd/system/default.target
#runlevel 5
ln -sf /lib/systemd/system/graphical.target /etc/systemd/system/default.target