Why am I getting the error "connection refused" in Python? (Sockets)

Question

I'm new to Sockets, please excuse my complete lack of understanding.

I have a server script(server.py):

#!/usr/bin/python

import socket #import the socket module

s = socket.socket() #Create a socket object
host = socket.gethostname() #Get the local machine name
port = 12397 # Reserve a port for your service
s.bind((host,port)) #Bind to the port

s.listen(5) #Wait for the client connection
while True:
    c,addr = s.accept() #Establish a connection with the client
    print "Got connection from", addr
    c.send("Thank you for connecting!")
    c.close()

and client script (client.py):

#!/usr/bin/python 

import socket #import socket module

s = socket.socket() #create a socket object
host = '192.168.1.94' #Host i.p
port = 12397 #Reserve a port for your service

s.connect((host,port))
print s.recv(1024)
s.close

I go to my desktop terminal and start the script by typing:

python server.py

after which, I go to my laptop terminal and start the client script:

python client.py

but I get the following error:

File "client.py", line 9, in

s.connect((host,port))

File "/usr/lib/python2.7/socket.py", line 224, in meth

return getattr(self._sock,name)(*args)

socket.error: [Errno 111] Connection refused

I've tried using different port numbers to no avail. However, I was able to get the host name using the same ip and the gethostname() method in the client script and I can ping the desktop (server).

Answer 1

Instead of

host = socket.gethostname() #Get the local machine name
port = 12397 # Reserve a port for your service
s.bind((host,port)) #Bind to the port

you should try

port = 12397 # Reserve a port for your service
s.bind(('', port)) #Bind to the port

so that the listening socket isn't too restricted. Maybe otherwise the listening only occurs on one interface which, in turn, isn't related with the local network.

One example could be that it only listens to 127.0.0.1, which makes connecting from a different host impossible.

Answer 2

This error means that for whatever reason the client cannot connect to the port on the computer running server script. This can be caused by few things, like lack of routing to the destination, but since you can ping the server, it should not be the case. The other reason might be that you have a firewall somewhere between your client and the server - it could be on server itself or on the client. Given your network addressing, I assume both server and client are on the same LAN, so there shouldn't be any router/firewall involved that could block the traffic. In this case, I'd try the following:

• check if you really have that port listening on the server (this should tell you if your code does what you think it should): based on your OS, but on linux you could do something like netstat -ntulp
• check from the server, if you're accepting the connections to the server: again based on your OS, but telnet LISTENING_IP LISTENING_PORT should do the job
• check if you can access the port of the server from the client, but not using the code: just us the telnet (or appropriate command for your OS) from the client

and then let us know the findings.

Answer 3

Assume s = socket.socket() The server can be bound by following methods: Method 1:

host = socket.gethostname()
s.bind((host, port))

Method 2:

host = socket.gethostbyname("localhost")  #Note the extra letters "by"
s.bind((host, port))

Method 3:

host = socket.gethostbyname("192.168.1.48")
s.bind((host, port))

If you do not exactly use same method on the client side, you will get the error: socket.error errno 111 connection refused.

So, you have to use on the client side exactly same method to get the host, as you do on the server. For example, in case of client, you will correspondingly use following methods:

Method 1:

host = socket.gethostname() 
s.connect((host, port))

Method 2:

host = socket.gethostbyname("localhost") # Get local machine name
s.connect((host, port))

Method 3:

host = socket.gethostbyname("192.168.1.48") # Get local machine name
s.connect((host, port))

Hope that resolves the problem.