How do I find an open port in Linux?

Question

Is there some kind of system call that will return whether a port is available? Or at least a conventional way to do it that doesn't make your process a bad citizen?

At the moment this is how I'm doing it:

def find_open_port(min_port, max_port):
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    for port in range(min_port, max_port):
        if port > max_port:
            raise IOError('Could not find a free port between {0} and {1}'.format(min_port, max_port))
        try:
            s.bind(('localhost', port))
            return port
        except socket.error as error:
            if error.strerror == 'Address already in use':
                continue
            else:
                raise error

Yuck!

Check this..... http://stackoverflow.com/questions/2838244/get-open-tcp-port-in-python — avasal, Feb 14 '12 at 05:17
Are you looking for determining if a port is open in Linux in general? Or do you need it to be in Python? — Jack Leow, Feb 14 '12 at 05:24
In general, I was just using Python because its socket library is close to the metal. — Cera, Feb 14 '12 at 05:27
Considered it, but the port being unused doesn't mean the user has permission to bind to that port. — Cera, Feb 14 '12 at 10:54

score 12 · Accepted Answer · answered Feb 14 '12 at 05:24

12

The simplest way that I know of to check if a particular port is available is to try and bind to it or try to connect to it (if you want TCP). If the bind (or connect) succeeds, it was available (is in use).

However, if you simply want any open port, you can bind to port 0, and the opperating system will assign you a port.

answered Feb 14 '12 at 05:24

David Wolever

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Ah, that'll work. Will the operating system tell me what port it assigned me to somehow? – Cera Feb 14 '12 at 05:27
2

Sure, use [`socket.getsockname()`](http://docs.python.org/library/socket.html#socket.socket.getsockname). – Greg Hewgill Feb 14 '12 at 05:36

How do I find an open port in Linux?

1 Answers1