Linux sockets: Difference between revisions

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On a server, this is probably due to an old instance of the server that tries to bind to the same port and address [https://stackoverflow.com/questions/15198834/bind-failed-address-already-in-use].
On a server, this is probably due to an old instance of the server that tries to bind to the same port and address [https://stackoverflow.com/questions/15198834/bind-failed-address-already-in-use].


As a fix, try to bind with option <code>SO_REUSEADDR</code> and/or <code>SO_REUSEPORT</code>.
As a fix, try to bind with option <code>SO_REUSEADDR</code> and/or <code>SO_REUSEPORT</code>. From [https://stackoverflow.com/questions/24194961/how-do-i-use-setsockoptso-reuseaddr SO]:
<source lang="bash">
if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &(int){ 1 }, sizeof(int)) < 0)
error("setsockopt(SO_REUSEADDR) failed");
</source>



See [http://man7.org/linux/man-pages/man7/socket.7.html socket(7)] and [http://man7.org/linux/man-pages/man7/ip.7.html ip(7)] manpages.
For more information, see [http://man7.org/linux/man-pages/man7/socket.7.html socket(7)] and [http://man7.org/linux/man-pages/man7/ip.7.html ip(7)] manpages.

Revision as of 11:45, 17 September 2018

Tutorials

A thoough step-by-step example of client and socket code.
Simple example of client and server code using Linux sockets.

References

A very detailed answer about the differences between SO_REUSEADDR and SO_REUSEPORT.
A course on internet technologies, including Domain Naming (DNS...), the IP protocol, the TCP protocol, ...
  • Manpages:

Troubleshooting

Use errno / strerror to get error

if( bind(socket_desc,(struct sockaddr *)&server , sizeof(server)) < 0)
{
    printf("bind failed: %s (errno %d)", strerror(errno), errno);
    return 1;
}

Use netstat to get socket status

./server
# bind done
# Waiting for incoming connections...
# Connection accepted
# Handler assigned
# ^C

./server
# bind failed: Address already in use (errno 98)

netstat -a | grep 8888
# tcp        0      0 zavcxl0005:58888        165.225.76.32:http      ESTABLISHED
# tcp        0      0 zavcxl0005:48888        10.75.126.1:https       ESTABLISHED
# tcp        0      0 localhost.localdom:8888 localhost.localdo:50310 TIME_WAIT  

# ... So port is still in use

bind failed: Address already in use (errno 98)

Call to bind fails with error

bind failed: Address already in use (errno 98)

On a server, this is probably due to an old instance of the server that tries to bind to the same port and address [1].

As a fix, try to bind with option SO_REUSEADDR and/or SO_REUSEPORT. From SO:

if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &(int){ 1 }, sizeof(int)) < 0)
    error("setsockopt(SO_REUSEADDR) failed");


For more information, see socket(7) and ip(7) manpages.