How to open port 8000 on Ubuntu 12.04?

Question

On my Ubuntu 12.04 VM an app (Tryton) is running correctly on port 8000, when used locally. However, from outside I cannot connect to port 8000 via Internet. (Beforehand, I was using Windows Azure which has a user-friendly endpoint configuration.)

Netstat, run locally, reports the port as listening: (I've called this VM "NoConnection", to distinguish from below)

root@NoConnection:~# netstat -tupan | grep 8000
tcp        0      0 127.0.0.1:8000          0.0.0.0:*               LISTEN
10051/python
tcp        0      0 127.0.0.1:8000          127.0.0.1:58160         ESTABLISHED
10051/python
tcp        0      0 127.0.0.1:58160         127.0.0.1:8000          ESTABLISHED
10860/python

Checking locally with nmap seems ok as well:

root@NoConnection:~# nmap -v -A -PN localhost

Starting Nmap 5.21 ( http://nmap.org ) at 2014-03-05 09:55 EST
NSE: Loaded 36 scripts for scanning.
Initiating SYN Stealth Scan at 09:55
Scanning localhost (127.0.0.1) [1000 ports]
Discovered open port 22/tcp on 127.0.0.1
Discovered open port 3389/tcp on 127.0.0.1
Discovered open port 8000/tcp on 127.0.0.1
Discovered open port 631/tcp on 127.0.0.1
Discovered open port 5432/tcp on 127.0.0.1
Discovered open port 5910/tcp on 127.0.0.1
Completed SYN Stealth Scan at 09:55, 0.03s elapsed (1000 total ports)


PORT     STATE SERVICE       VERSION
22/tcp   open  ssh           OpenSSH 5.9p1 Debian 5ubuntu1.1 (protocol 2.0)
631/tcp  open  ipp           CUPS 1.5
3389/tcp open  microsoft-rdp xrdp
5432/tcp open  postgresql    PostgreSQL DB
5910/tcp open  vnc           VNC (protocol 3.8)
8000/tcp open  http-alt?

Port 8000 is Tryton ERP by the way, but nmap doesn't know that.

However, a nmap scan from a different machine *does not* find the open port:

root@WorksRight:~# nmap -v -A -PN IP_of_NoConnect_VM

Starting Nmap 5.21 ( http://nmap.org ) at 2014-03-05 15:00 UTC
NSE: Loaded 36 scripts for scanning.
Initiating Parallel DNS resolution of 1 host. at 15:00
Completed Parallel DNS resolution of 1 host. at 15:00, 0.08s elapsed
Initiating SYN Stealth Scan at 15:00
Scanning IP_of_NoConnect_VM [1000 ports]
Discovered open port 22/tcp on IP_of_NoConnect_VM
Discovered open port 3389/tcp on IP_of_NoConnect_VM
Discovered open port 5910/tcp on IP_of_NoConnect_VM
Completed SYN Stealth Scan at 15:00, 0.13s elapsed (1000 total ports)

I guess this is something not particular to the Tryton App, but to the way the Linux VM is set up with its ports.

For reference, on a working, different VM (on Windows Azure) where Tryton is configured correctly and accessible via Port 8000, the netstat output for port 8000 reads:

root@WorksRight:~# netstat -tupan | grep 8000
tcp6       0      0 :::8000                 :::*                    LISTEN
1310/python
tcp6       0      0 127.0.0.1:8000          127.0.0.1:36818         TIME_WAIT
-
tcp6       0      0 127.0.0.1:8000          127.0.0.1:36820         TIME_WAIT
-
tcp6       0      0 127.0.0.1:8000          127.0.0.1:36814         TIME_WAIT
-
tcp6       0      0 127.0.0.1:8000          127.0.0.1:36813         TIME_WAIT
-

And on the not-connecting VM it shows:

root@NoConnection:~# netstat -tupan | grep 8000
tcp        0      0 127.0.0.1:8000          0.0.0.0:*               LISTEN
10051/python
tcp        0      0 127.0.0.1:8000          127.0.0.1:58160         ESTABLISHED
10051/python
tcp        0      0 127.0.0.1:58160         127.0.0.1:8000          ESTABLISHED
10860/python

And of course, yes, I have checked, both machines have the port open in the application-specific trytond.conf file:

#This file is part of Tryton.  The COPYRIGHT file at the top level of
#this repository contains the full copyright notices and license terms.
[options]

# Activate the json-rpc protocol
jsonrpc = *:8000

Answer 1

As it turned out, the application server had just not restarted correctly and hence not read in the changes to the config file.

The more detailed answer is here: Tryton client doesn't connect via Internet port 8000.