I have a lan of about 10-15 clients (depends on counting tablets and so on..). To access them from one station I use tightvnc which works like a charm - up to now. Sometimes I cannot access and I don't know why. When I access manually and so on, then it works, out of the blue. Are there some commonly known "features" I don't know?

closed as too broad by Rui F Ribeiro, Thomas Dickey, Jeff Schaller, msp9011, Totor Sep 5 '18 at 6:23

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  • I don't understand how this is too broad. I immediately recognized what his problem might be based on his title. – ron Sep 5 '18 at 19:25

VNC works on ports 5900 and up; 5900 for the service I believe then 5900+n for each n user desktops.

so if you are the 7th user for example and you get desktop :7, you would need port 5907 in addition to 5900 being opened in your firewall.

depending on your linux distribution, they sometimes manage only a few ports upward or 5900, your 10-15 clients is likely exceeding that and your firewall may be blocking VNC for those desktops.

a not uncommon but not necessarily correct practice is to just open ports 5900:5999 in your firewall, which would account for up to 99 users... or disable firewall if that is acceptable on your LAN

  • Interesting, thanks a lot! I will apply this. To add something I should have done before: When I restart the computer, then it works from the beginning on. Hence, my feeling is that it appears when the computer is idle and not used for a while (say >15min). Could this be possible somehow? – Ben Sep 5 '18 at 9:47
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    rebooting will clear the VNC connections list, starting in the basement at 5900 again and would work, as more and more user's connect going to ports 5900+n is when the firewall would start blocking. – ron Sep 5 '18 at 19:16
  • I use SUSE, and by default they open ports 5900:5904 where 5901 is a non-persistent VNC remote desktop with resolution of 800x600; 5902 is :2 at 1024x768 res; and 5903 is :3 at 1600x1200 res. Therefore as users do vncserver to get a persistent remote connection for themself things are fine for the first three users, user #4 and higher would get blocked by firewall and vnc would not work for them with no error message given. – ron Sep 5 '18 at 19:19
  • as such anyone getting desktop :1, :2, or :3 is fine. When it goes to :4 and above at port 5904 and above would be blocked by firewall, unless the firewall is customized. this is something that may be different for every linux distribution: rhel, sles, debian and so on. – ron Sep 5 '18 at 19:29
  • Thanks a lot again! This information is very helpful to understand the ongoing processes. I just noticed that this SE site is dedicated for unix/linux but I'm using tightvnc on windows because I have to due to business requirements. Personally I prefer linux too :) – Ben Sep 11 '18 at 6:47

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