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port-for

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port-for is a command-line utility and a python library that helps with local TCP ports management.

It can find an unused TCP localhost port and remember the association:

$ sudo port-for foo
37987

This can be useful when you are installing a stack of software with multiple parts needing port numbers.

Note

If you're looking for a temporary port then socket.bind((host, 0)) is your best bet:

>>> import socket
>>> s = socket.socket()
>>> s.bind(("", 0))
>>> s.getsockname()
('0.0.0.0', 54485)

port-for is necessary when you need persistent free local port number.

port-for is the exact opposite of s.bind((host, 0)) in the sense that it shouldn't return ports that s.bind((host, 0)) may return (because such ports are likely to be temporary used by OS).

There are several rules port-for is trying to follow to find and return a new unused port:

  1. Port must be unused: port-for checks this by trying to connect to the port and to bind to it.
  2. Port must be IANA unassigned and otherwise not well-known: this is acheived by maintaining unassigned ports list (parsed from IANA and Wikipedia).
  3. Port shouldn't be inside ephemeral port range. This is important because ports from ephemeral port range can be assigned temporary by OS (e.g. by machine's IP stack) and this may prevent service restart in some circumstances. port-for doesn't return ports from ephemeral port ranges configured at the current machine.
  4. Other heuristics are also applied: port-for tries to return a port from larger port ranges; it also doesn't return ports that are too close to well-known ports.

Installation

System-wide using easy_install (something like python-setuptools should be installed):

sudo pip install port-for

or:

sudo easy_install port-for

or inside a virtualenv:

pip install port-for

Script usage

port-for <foo> script finds an unused port and associates it with <foo>. Subsequent calls return the same port number.

This utility doesn't actually bind the port or otherwise prevents the port from being taken by another software. It tries to select a port that is less likely to be used by another software (and that is unused at the time of calling of course). Utility also makes sure that port-for bar won't return the same port as port-for foo on the same machine.

$ sudo port-for foo
37987

$ port-for foo
37987

You may want to develop some naming conventions (e.g. prefix your app names) in order to enable multiple sites on the same server:

$ sudo port-for example.com/apache
35456

Please note that port-for script requires read and write access to /etc/port-for.conf. This usually means regular users can read port values but sudo is required to associate a new port.

List all associated ports:

$ port-for --list
foo: 37987
example.com/apache: 35456

Remove an association:

$ sudo port-for --unbind foo
$ port-for --list
example.com/apache: 35456

Library usage

>>> import port_for
>>> port_for.select_random()
37774

>>> port_for.select_random()
48324

>>> 80 in port_for.available_good_ports()
False

Dig into source code for more.

Contributing

Development happens at github: https://github.com/kmike/port-for/

Issue tracker: https://github.com/kmike/port-for/issues/new

In order to run tests make sure you have tox installed, then type

tox

from the source checkout.