What opens a TCP port

veryangryman

Hi

I use the following command

lsof -i :50340

To check if a certain TCP port is "listening"


When it is not listening, how do you get it to listen. Is it done from the application itself or is there another way

Webmonkey

An application must open a socket that listens on a specific port.

For example, an FTP server would listen on port 21, a web server would listen on port 80 etc.

IRLConor

Q: What opens a TCP port?
A: A TCP Harbour Master.



Seriously though: have a look at netcat (man nc) and you should be able to easily get something listening on a given port. What exactly are you trying to do?

Naikon

Just to note, there are two specific types of sockets at least under Unix OS's.

Domain sockets are used for interprocess communication between local applications
in Unix(Process communication) whereas Network sockets are used for you guessed
it...network communication over TCP/IP or whatever the hell you want.

Naikon

veryangryman wrote: »

Hi

I use the following command

lsof -i :50340

To check if a certain TCP port is "listening"


When it is not listening, how do you get it to listen. Is it done from the application itself or is there another way

There is a script associated with the application under /etc/init.d/<service.name>
for SysV like distros like Debian or /etc/rc.d/rc.<service_name> or for BSD like systems.

So Apache is started with /etc/init.d/apache start, which binds apache to port 80 or a user
specified port specified by the config file "httpd.conf", which is read by the server at runtime.

The C application itself opens the port on behalf of the program, by using low
level socket interfaces detailed in the C standard library.

clearz

An operating system implements a network stack wich usually handles TCP/IP Each network layer is separate to the one above check out this for more info
http://en.wikipedia.org/wiki/OSI_model