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

User · Answer

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

User · Answer

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

User · Answer

According to this link     Actually  SO REUSEADDR flag can lead to much greater consequences    SO REUSADDR permits you to use a port that is stuck in TIME WAIT  but   you still can not use that port to establish a connection to the last   place it connected to  What  Suppose I pick local port 1010  and   connect to foobar com port 300  and then close locally  leaving that   port in TIME WAIT  I can reuse local port 1010 right away to connect   to anywhere except for foobar com port 300    However you can completely avoid TIME WAIT state by ensuring that the remote end initiates the closure  close event   So the server can avoid problems by letting the client close first  The application protocol must be designed so that the client knows when to close  The server can safely close in response to an EOF from the client  however it will also need to set a timeout when it is expecting an EOF in case the client has left the network ungracefully  In many cases simply waiting a few seconds before the server closes will be adequate    I also advice you to learn more about networking and network programming  You should now at least how tcp protocol works  The protocol is quite trivial and small and hence  may save you a lot of time in future   With netstat command you can easily see which programs    program name pid  tuple  are binded to which ports and what is the socket current state  TIME WAIT  CLOSING  FIN WAIT and so on   A really good explanation of linux network configurations can be found https   serverfault com questions 212093 how-to-reduce-number-of-sockets-in-time-wait

User · Answer

As Felipe Cruze mentioned  you must set the SO REUSEADDR before binding  I found a solution on another site - solution on other site  reproduced below     The problem is that the SO REUSEADDR socket option must be set before   the address is bound to the socket   This can be done by subclassing   ThreadingTCPServer and overriding the server bind method as follows     import SocketServer  socket  class MyThreadingTCPServer SocketServer ThreadingTCPServer       def server bind self           self socket setsockopt socket SOL SOCKET  socket SO REUSEADDR  1          self socket bind self server address

User · Answer

In case you face the problem using TCPServer or SimpleHTTPServer  override SocketServer TCPServer allow reuse address  python 2 7 x    or socketserver TCPServer allow reuse address  python 3 x  attribute  class MyServer SocketServer TCPServer       allow reuse address   True  server   MyServer  HOST  PORT   MyHandler  server serve forever

User · Answer

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

User · Answer

socket socket   should run before socket bind   and use REUSEADDR as said

User · Answer

Try using the SO REUSEADDR socket option before binding the socket   comSocket setsockopt socket SOL SOCKET  socket SO REUSEADDR  1    Edit  I see you re still having trouble with this   There is a case where SO REUSEADDR won t work   If you try to bind a socket and reconnect to the same destination  with SO REUSEADDR enabled   then TIME WAIT will still be in effect   It will however allow you to connect to a different host port   A couple of solutions come to mind   You can either continue retrying until you can gain a connection again   Or if the client initiates the closing of the socket  not the server   then it should magically work

User · Answer

I think the best way is just to kill the process on that port  by typing in the terminal fuser -k  PORT NUMBER  tcp  e g  fuser -k 5001 tcp

User · Answer

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  lt app-name gt  py   always worked well when SO REUSEADDR was set to true  The new Thonny IDE or Idle3 IDE did not have this problem

User · Answer

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

User · Answer

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

[python] Python: Binding Socket: "Address already in use"

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