I got VNCserver working per:

https://www.tecmint.com/install-and-configure-vnc-server-in-CentOS-7/

Then I went to set up a second instance, and have that for logging on to root:

==========

cp /lib/systemd/system/vncserver@.service
/etc/systemd/system/vncserver@:2.service

vi /etc/systemd/system/vncserver@\:2.service

replace with root

systemctl daemon-reload systemctl start VNCserver@:2

==========

I got the message:

Job for VNCserver@:2.service failed because a configured resource limit was exceeded. See “systemctl status VNCserver@:2.service” and “journalctl -xe” for details.

#systemctl -l status VNCserver@:2.service

● VNCserver@:2.service – Remote desktop service (VNC)
   Loaded: loaded (/etc/systemd/system/vncserver@:2.service; disabled;
vendor preset: disabled)
   Active: failed (Result: resources) since Wed 2018-08-01 08:45:19
EDT; 1min 8s ago
  Process: 2267 ExecStart=/usr/sbin/runuser -l root -c
/usr/bin/vncserver %i (code=exited, status=0/SUCCESS)
  Process: 2260 ExecStartPre=/bin/sh -c /usr/bin/vncserver -kill %i >
/dev/null 2>&1 || : (code=exited, status=0/SUCCESS)

Aug 01 08:45:14 localhost systemd[1]: Starting Remote desktop service
(VNC)… Aug 01 08:45:19 localhost systemd[1]: PID file
/home/root/.vnc/localhost:2.pid not readable (yet?) after start. Aug 01 08:45:19 localhost systemd[1]: Failed to start Remote desktop service (VNC). Aug 01 08:45:19 localhost systemd[1]: Unit VNCserver@:2.service entered failed state. Aug 01 08:45:19 localhost systemd[1]: VNCserver@:2.service failed.

===========

And yet, I am able to connect to 5902!  It is running.

cat /root/.vnc/localhost:2.log

shows:

Xvnc TigerVNC 1.8.0 – built Apr 11 2018 21:04:25
Copyright (C) 1999-2017 TigerVNC Team and many others (see README.txt)
See http://www.tigervnc.org for information on TigerVNC. Underlying X server release 11903000, The X.Org Foundation

Wed Aug  1 08:45:16 2018
 vncext:      VNC extension running!
 vncext:      Listening for VNC connections on all interface(s), port 5902
 vncext:      created VNC server for screen 0

Wed Aug  1 08:45:23 2018
 ComparingUpdateTracker: 0 pixels in / 0 pixels out
 ComparingUpdateTracker: (1:nan ratio)

Wed Aug  1 08:51:01 2018
 Connections: accepted: 192.168.160.20::53318
 SConnection: Client needs protocol version 3.8
 SConnection: Client requests security type VeNCrypt(19)
 SVeNCrypt:   Client requests security type TLSVnc (258)

etc.

========

what is going on with systemctl?

thanks