Socket error: Address already in use

Question

I have a CherryPy script that I frequently run to start a server. Today I was having to start and stop it a few times to fix some bugs in a config file, and I guess the socket

Answer 1

You could find the process and kill it by doing:

ps aux | grep python

, finding the process ID, and stopping it manually by doing:

sudo kill -9 PID

replacing PID with your PID.

I often have to do this while testing with Flask/CherryPy. Would be interested to see if there's an easier way (for e.g. to prevent it in the first place)

Answer 2

Much more easier to do it by:

Check the PID(:5000 is the host since I've been running on 127.0.0.1:5000):
$ lsof -i :5000
Then kill it:
$ sudo kill -9 PID

Answer 3

You can try the following

from socket import *

sock=socket()
sock.setsockopt(SOL_SOCKET, SO_REUSEADDR, 1)
# then bind

From the docs:

The SO_REUSEADDR flag tells the kernel to reuse a local socket in TIME_WAIT state, without waiting for its natural timeout to expire.

Here's the complete explanation:

Running an example several times with too small delay between executions, could lead to this error:

socket.error: [Errno 98] Address already in use

This is because the previous execution has left the socket in a TIME_WAIT state, and can’t be immediately reused.

There is a socket flag to set, in order to prevent this, socket.SO_REUSEADDR:

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.bind((HOST, PORT))