[Spice-devel] Gnome vino-server not listening to IPv4

[Christophe de Dinechin]

Hello,


[If you don’t use VNC to access a Linux host, you can safely skip this e-mail]

I recently lost access to three Linux hosts over VNC, and it took me long enough to figure out what was going on that I thought I’d share and ask for advice. This is recorded as https://bugzilla.redhat.com/show_bug.cgi?id=1437619 <https://bugzilla.redhat.com/show_bug.cgi?id=1437619>, seems to be related to others, e.g. https://bugzilla.redhat.com/show_bug.cgi?id=703009 <https://bugzilla.redhat.com/show_bug.cgi?id=703009>.

Symptoms: VNC access to a Linux host does not work. Local access with remote-viewer vnc://localhost:5900 <vnc://localhost:5900> works. Remote access with remote-viewer vnc://myhost:5900 <vnc://myhost:5900> does not. Doing lsof -i -P | grep vino shows that the vino-server is only listening to IPv6.

Apparent cause: In some conditions, which apparently involve localhost resolving as ::1, vino-server only listens to IPv6. When this is the case, you get:

ddd at muse ~> lsof -i -R | grep vino
vino-serv 3326 1309  ddd   12u  IPv6  75662      0t0  TCP *:rfb (LISTEN)

When it’s working “normally”, you get:

ddd at muse ~> lsof -i -R | grep vino
vino-serv 3326 1309  ddd   12u  IPv4  86485      0t0  TCP muse.dinechin.org:rfb (LISTEN)
vino-serv 3326 1309  ddd   14u  IPv6  86486      0t0  TCP muse.dinechin.org:rfb (LISTEN)
vino-serv 3326 1309  ddd   15u  IPv6  86487      0t0  TCP muse.dinechin.org:rfb (LISTEN)
vino-serv 3326 1309  ddd   16u  IPv4  86488      0t0  TCP muse.dinechin.org:rfb->192.168.77.22:54781 (ESTABLISHED)

Workaround: I found two workarounds. You may need one or both, I’ve not seen consistent results between my hosts.

	#1: Disable localhost resolution to ::1. In my case, this means:
		a) Removing the resolution in my local DNS, in my case it was in /etc/bind/db.local
		b) Commenting out the ::1 entry in /etc/hosts.

	#2: Force the server to listen on a specific interface (only had to do it on one of my hosts)
		a) Run dconf-editor
		b) Go to /org/gnome/desktop/remote-access/network-interface
		c) Set “Use default value” to off
		d) Enter the name of your network card, e.g. enp4s0 for my machine, in the “Custom value” field.

Cause of change: I am not sure, because I changed both my DNS (now bind9 on a local machine) and did a dnf update. I saw the problem after the update, but it may just be because the network restarted, since in at least one case, vino-server had not actually been updated.


Hope this helps someone ;-)

Christophe



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