On a headless build host you start a virtual desktop with `vncserver :2`. A colleague on the same LAN asks which TCP port must be reachable so that their viewer can connect. Which port do you name?
LPIC-1 Exam 102-500, objective 106. User interfaces and desktops hard
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How these questions are written — where each question comes from, what the verification ledger records, and what happens when one is found wrong.
The options
Not correct 5900
Wrong. 5900 is the base port, which corresponds to display :0. The display number is added to the base, so :2 is not served there.
Correct 5902
Correct. A VNC server on display :N listens on TCP 5900 + N, so display :2 is reached on 5902 and the viewer is pointed at buildhost:2 or buildhost:5902.
Not correct 6002
Wrong, but for an instructive reason. 6000 + N is the port range of the X protocol itself, so 6002 is where an X server for display :2 would listen if it accepted TCP connections. That is a different protocol from VNC's RFB.
Not correct 5802
Wrong. 5800 + N is the historic HTTP port some VNC servers offered for a browser-delivered Java viewer. It serves a web page, not the RFB session, and many builds no longer offer it.
Why
VNC carries the Remote Framebuffer protocol on TCP 5900 plus the display number, so :1 is 5901, :2 is 5902 and so on; viewers accept either the display shorthand or the full port. Keep that separate from the X protocol's own 6000 plus display number. Because RFB itself is only weakly protected, the usual practice is to bind the server to localhost and reach it through an ssh tunnel rather than opening 590x on the firewall.
Where this comes from
- Cited
- manual page vncserver(1)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 106 and space the ones you get wrong.
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