The VNC That Wouldn’t Connect

Date: August 18, 2023 Duration: Most of the day Messages: 126 Issue: VNC server installation on Debian Result: TigerVNC working after complete purge

The Problem

I’d tried to install VNC on this Debian box before. Multiple times. Different packages. Each attempt left behind config files, systemd units, and broken state.

Now nothing worked. Fresh install attempts would fail because old configs conflicted with new ones.

Time to nuke it from orbit.

The Purge

First: find everything VNC-related and remove it.

# Remove all VNC packages
apt purge tigervnc-* tightvnc* x11vnc vnc4server realvnc-* -y

# Find leftover configs
find /etc -name "*vnc*" 2>/dev/null
find /home -name "*vnc*" 2>/dev/null
find ~/.vnc -type f 2>/dev/null

# Remove them
rm -rf ~/.vnc
rm -rf /etc/vnc*
rm -f /etc/systemd/system/*vnc*

Reload systemd to forget the old units:

systemctl daemon-reload

The Fresh Install

TigerVNC. It’s the most actively maintained, works with modern desktops.

apt update
apt install tigervnc-standalone-server tigervnc-common -y

Set the VNC password:

vncpasswd
# Enter password twice
# "Would you like to enter a view-only password?" - No

The First Failure

Started the server:

vncserver :1

Connected from my laptop:

Connection refused

Check if it’s running:

ss -tlnp | grep 590
# Nothing

Not running. Check the log:

cat ~/.vnc/*.log

Xvnc TigerVNC 1.x - built...
...
(EE) Fatal server error:
(EE) Cannot establish any listening sockets

Port 5901 was blocked. By what?

The Port Conflict

ss -tlnp | grep 5901
# Shows nothing

lsof -i :5901
# Shows nothing

Not a port conflict. Firewall?

iptables -L -n | grep 590
# Nothing blocking

Not the firewall. What then?

Turns out: the previous VNC installation had created a socket file that still existed. TigerVNC was trying to use it and failing.

rm -rf /tmp/.X1-lock
rm -rf /tmp/.X11-unix/X1

Try again:

vncserver :1

New 'debian:1' desktop is debian:1
Starting applications specified in /home/argo/.vnc/xstartup

Finally.

The Black Screen

Connected from the laptop. Got a connection. Saw… nothing. Black screen with an X cursor.

The VNC server was running, but no desktop environment was starting.

Check xstartup:

cat ~/.vnc/xstartup

Empty. Or worse, pointing to a desktop that wasn’t installed.

The xstartup Fix

Created a working xstartup:

#!/bin/sh
unset SESSION_MANAGER
unset DBUS_SESSION_BUS_ADDRESS
exec startxfce4 &

Made it executable:

chmod +x ~/.vnc/xstartup

Killed the VNC server and restarted:

vncserver -kill :1
vncserver :1

Connected. XFCE desktop appeared. Finally working.

The Systemd Unit

Manual starts are annoying. Made it a service:

cat > /etc/systemd/system/[email protected] << 'EOF'
[Unit]
Description=VNC Server for display %i
After=network.target

[Service]
Type=forking
User=argo
ExecStart=/usr/bin/vncserver :%i -geometry 1920x1080 -depth 24
ExecStop=/usr/bin/vncserver -kill :%i

[Install]
WantedBy=multi-user.target
EOF

Enable and start:

systemctl daemon-reload
systemctl enable vncserver@1
systemctl start vncserver@1

Now VNC starts on boot, survives reboots, and can be managed with systemctl.

What I Learned

Purge completely before reinstalling. Half the debugging was fighting ghosts from previous attempts.

Check socket files. /tmp/.X* files can block new sessions even when no process is running.

xstartup is everything. Without it, you get a black screen. With the wrong one, you get a broken desktop.

126 messages for a VNC server. Sometimes the simple things aren’t simple.

The Final Config

~/.vnc/
├── config          # Resolution and depth settings
├── passwd          # Encrypted VNC password
├── xstartup        # Desktop startup script
└── debian:1.log    # Session log

VNC on port 5901, XFCE desktop, auto-starting on boot. Remote access to the pentesting lab: achieved.

When something won’t install cleanly, the answer is usually: remove everything and start over.

The VNC That Wouldn't Connect