VNC Server port is closed

Question

I installed TigerVNC server on my Ubuntu server but I can't connect to it. The server is running but when I try to scan for open ports (in LAN) using my phone, 5901 is closed.

Output of nmap localhost:

Starting Nmap 7.80 ( https://nmap.org ) at 2020-06-25 08:02 UTC
Nmap scan report for localhost (127.0.0.1)
Host is up (0.00026s latency).
Not shown: 995 closed ports
PORT     STATE SERVICE
22/tcp   open  ssh
80/tcp   open  http
631/tcp  open  ipp
5901/tcp open  vnc-1

Nmap done: 1 IP address (1 host up) scanned in 0.13 seconds

I think the problem is here. Output of nmap 192.168.0.101:

Starting Nmap 7.80 ( https://nmap.org ) at 2020-06-25 08:05 UTC
Nmap scan report for cloud.local (192.168.0.101)
Host is up (0.00039s latency).
Not shown: 998 closed ports
PORT   STATE SERVICE
22/tcp open  ssh
80/tcp open  http

Nmap done: 1 IP address (1 host up) scanned in 0.58 seconds

What I've already tried:

• Allow port 5901/tcp in firewall
• Disable firewall and reboot

EDIT: Output of nmap 192.168.0.101 -p 5900-5901:

Starting Nmap 7.80 ( https://nmap.org ) at 2020-06-25 09:50 UTC
Nmap scan report for cloud.local (192.168.0.101)
Host is up (0.00032s latency).

PORT     STATE  SERVICE
5900/tcp closed vnc
5901/tcp closed vnc-1

Nmap done: 1 IP address (1 host up) scanned in 0.12 seconds

Solution

I asked another question and this is specific to TigerVNC Server.

From https://askubuntu.com/a/1254109/1027810 :

TigerVNC by default listens only on the loopback network interface. This is good for security, so that only you on the very same computer can connect.

Of course, if you want to connect remotely, you need to specifically specify it as follows:

1. When you start the server from the command line, add -localhost no to the command line.

   tigervncserver -localhost no :1

2. Configure TigerVNC to permanently listen to all network interfaces in /etc/vnc.conf. Add the following. Note that the configuration file gives the impression that no is the default. They do not follow the convention that if a configuration is commented out in the config file, it should have the default value (and not the other value you would normally change to).

   $localhost = "no";

Comments

[bhordupur]

The reason it did not scan port 5901 because lIRC it does scan the most common 1000 ports for each protocol. try to add -p flag and mention the range which can cover 5901

[Parsa Mousavi]

Are you sure the error is about the port being closed ? Try NMAP with the -p5000-6000 option.What's exactly the error messages you get when running the client in the terminal ?

[bhordupur]

Look at this doc nmap.org/book/man-port-specification.html

[adazem009]

@Mousavi Yes, when I try to scan port range 5900-5902 using my mobile phone, these ports are closed.

[bhordupur]

have you tried to check list of open ports using netstat or similar other than nmap in your systems?

[adazem009]

@bhordupur No, I only tried to scan it via Net Analyzer app for Android.

[bhordupur]

Two things at this moment I can think about to trouble shoot the problem (1) making sure port is listening (2) specify port range if (1) satisfied and (2) does not work then I will head to next step of troubleshooting

[bhordupur]

in the next step i would add nmap -p 1-65535 or nmap -p- meaning same

[bhordupur]

and TigerVNC server on my Ubuntu server is running and you are not able to connect meaning something is blocking you. check your iptables what is blocked

[bhordupur]

What firewall are you using?

[adazem009]

@bhordupur I'm using ufw and it's disabled because I even can't connect to SSH when it's enabled.

[adazem009]

Let us continue this discussion in chat.

[adazem009]

Edit added above.

[adazem009]

I was running a VNC server on my previous server and it was working fine.

[djangofan]

I tried this change in my /etc/systemd/system/[email protected] file, and now my service will not start up. Not convinced this is the answer. I am using TightVNC, not Tiger.