Python: Binding Socket: “Address already in use”

Question

I have a question regarding client socket on TCP/IP network. Let's say I use

try:

    comSocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    comSocket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)

except socket.error, msg:

    sys.stderr.write("[ERROR] %s\n" % msg[1])
    sys.exit(1)

try:
    comSocket.bind(('', 5555))

    comSocket.connect()

except socket.error, msg:

    sys.stderr.write("[ERROR] %s\n" % msg[1])

    sys.exit(2)

The socket created will be bound to port 5555. The problem is that after ending the connection

comSocket.shutdown(1)
comSocket.close()

Using wireshark, I see the socket closed with FIN,ACK and ACK from both sides, I can't use the port again. I get the following error:

[ERROR] Address already in use

I wonder how can I clear the port right away so that next time I still can use that same port.

comSocket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)

setsockopt doesn't seem to be able to resolve the problem Thank you!

Answer 1

another solution, in development environment of course, is killing process using it, for example

def serve():
    server = HTTPServer(('', PORT_NUMBER), BaseHTTPRequestHandler)
    print 'Started httpserver on port ' , PORT_NUMBER
    server.serve_forever()
try:
    serve()
except Exception, e:
    print "probably port is used. killing processes using given port %d, %s"%(PORT_NUMBER,e)
    os.system("xterm -e 'sudo fuser -kuv %d/tcp'" % PORT_NUMBER)
    serve()
    raise e

Answer 2

I found another reason for this exception. When running the application from Spyder IDE (in my case it was Spyder3 on Raspbian) and the program terminated by ^C or an exception, the socket was still active:

sudo netstat -ap | grep 31416
tcp  0  0 0.0.0.0:31416  0.0.0.0:*    LISTEN      13210/python3

Running the program again found the "Address already in use"; the IDE seems to start the new 'run' as a separate process which finds the socket used by the previous 'run'.

socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)

did NOT help.

Killing process 13210 helped. Starting the python script from command-line like

python3 <app-name>.py

always worked well when SO_REUSEADDR was set to true. The new Thonny IDE or Idle3 IDE did not have this problem.

Answer 3

For me the better solution was the following. Since the initiative of closing the connection was done by the server, the setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) had no effect and the TIME_WAIT was avoiding a new connection on the same port with error:

[Errno 10048]: Address already in use. Only one usage of each socket address (protocol/IP address/port) is normally permitted 

I finally used the solution to let the OS choose the port itself, then another port is used if the precedent is still in TIME_WAIT.

I replaced:

self._socket.bind((guest, port))

with:

self._socket.bind((guest, 0))

As it was indicated in the python socket documentation of a tcp address:

If supplied, source_address must be a 2-tuple (host, port) for the socket to bind to as its source address before connecting. If host or port are ‘’ or 0 respectively the OS default behavior will be used.

Answer 4

Here is the complete code that I've tested and absolutely does NOT give me a "address already in use" error. You can save this in a file and run the file from within the base directory of the HTML files you want to serve. Additionally, you could programmatically change directories prior to starting the server

import socket
import SimpleHTTPServer
import SocketServer
# import os # uncomment if you want to change directories within the program

PORT = 8000

# Absolutely essential!  This ensures that socket resuse is setup BEFORE
# it is bound.  Will avoid the TIME_WAIT issue

class MyTCPServer(SocketServer.TCPServer):
    def server_bind(self):
        self.socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        self.socket.bind(self.server_address)

Handler = SimpleHTTPServer.SimpleHTTPRequestHandler

httpd = MyTCPServer(("", PORT), Handler)

# os.chdir("/My/Webpages/Live/here.html")

httpd.serve_forever()

# httpd.shutdown() # If you want to programmatically shut off the server

Answer 5

I know you've already accepted an answer but I believe the problem has to do with calling bind() on a client socket. This might be OK but bind() and shutdown() don't seem to play well together. Also, SO_REUSEADDR is generally used with listen sockets. i.e. on the server side.

You should be passing and ip/port to connect(). Like this:

comSocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
comSocket.connect(('', 5555))

Don't call bind(), don't set SO_REUSEADDR.

Answer 6

You need to set the allow_reuse_address before binding. Instead of the SimpleHTTPServer run this snippet:

Handler = SimpleHTTPServer.SimpleHTTPRequestHandler
httpd = SocketServer.TCPServer(("", PORT), Handler, bind_and_activate=False)
httpd.allow_reuse_address = True
httpd.server_bind()
httpd.server_activate()
httpd.serve_forever()

This prevents the server from binding before we got a chance to set the flags.