The checklist ends suggesting a reboot command.
If you don't obey, you'll only get a black screen on a VNC connection.
That seems to break the spell: no reboots under linux!
After some investigation it seems that the cause was gdm not accepting tcp connections from Xvnc.
A full reboot is not necessary, just a gdm restart:
Find the gdm instance started by init:
# ps -ef --forest
search the process tree for something like this:
root 3621 1 0 14:35 ? 00:00:00 /usr/sbin/gdm-binary -nodaemon
root 3707 3621 0 14:35 ? 00:00:00 \_ /usr/sbin/gdm-binary -nodaemon
root 3713 3707 0 14:35 tty7 00:00:00 \_ /usr/bin/Xorg :0 -br -audit 0 -auth /var/gdm/:0.Xauth -nolisten tcp vt7
gdm 3734 3707 0 14:35 ? 00:00:00 \_ /usr/libexec/gdmgreeter
the parent gdm here has PID 3621
# kill -1 3621
The console X session will restart, and after that, VNC logins will work.
On RHEL/CentOS 6, you must use kill -9 to reload gdm, and the vnc-server package is called tigervnc-server