Hello,

I am running Ubuntu 10.04 on my Linode and wanted to open ports 2195 and 2196. I thought I could do it in /etc/services but that doesn't seem to work. Specifically, this is to send Push Notifications for mobile apps. Any help would be appreciated on how to open these ports. Thanks in advance.

Jim

Unless you specifically blocked the ports by setting up a firewall, the ports don't need to be opened (because they're not closed).

I installed the LAMP configuration. Does Apache automatically install a firewall? I didn't specifically activate one. Are there commands I can run in SSH to check and then open a port. I realize that all ports should be open but I would like to know how to manipulate them - if possible. Thanks.

Apache doesn't install any sort of firewall, although I don't know what the stackscript that you used does. It's not a matter of if ports are open are not, because there's nothing to be open.

It'd be like saying "Is the door open or closed?" when the question is moot because the door does not exist to begin with.

There are essentially 3 potential states for ports, looking at things from a basic perspective.

1. The port is closed by a firewall. You, or a script run by you, or a firewall actively setup by you, etc, would have to specifically close a port in order for it to be closed. Any messages sent to this port will either be ignored or rejected, depending on the settings.

2. The port is in use. This is what I believe you mean by "open". This includes ports specifically claimed by apache, postfix, etc. Essentially, programs on your server take control of a port, and any messages sent to that port will be given to that program.

3. The port exists, but is neither in use or closed. This is the state of every port on your server which is not specifically set as one of the above options. Messages sent here will be ignored, not because the port is closed, but because there is nowhere to send the message.

Not quite "ignored", because (barring something along the network path preventing it or local configuration to prevent its generation), attempting to make a connection to an unused port will generate a packet back (ICMP or TCP RST) indicating the connection was refused/port is unavailable. So it's more a positive rejection than no response.

Most firewall setups do, however, truly ignore/hide the absence of a port when they are protecting it and blocked traffic is received - no response at all back to the initiator of the traffic.

-- David