Python: Binding Socket: "Address already in use"

user_801807 0
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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!

python
13 Answers

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.

user_61117720

I had the same problem and I couldn't find any other solution (reuse options didn't work) except restarting Raspberry Pi each time. Then I found a workaround;

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

This means, define socket first, close it, then define again, so you can use the same port if it is stuck.

user_97586880
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