Address already in use

This error means an address is already in use, this is frequently due to a network port or socket being already claimed by another process. You can't have two processes listen on the same IP address/port pair at the same time unless they actively cooperate to do so. For example, when starting apache a second time without closing down the first connection you get in the logs

Address already in use: make_sock: could not bind to port 80

You can tell whats listening on a port by using

netstat -ap

(see netstat(8) for more information)

kill(1) the other program that is listening on that port and try again.

Usually you get this error when trying to start a daemon that is already running.

This also occurs when a TCP socket is still timing out. If you stop a program that was listening then restart it again quickly, you may find you get this error. In this case either wait a few minutes (4 should do); or in the case that it is your own program; use the code below.

To code around this call

unsigned int opt = 1; if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt))==-1) {

perror("setsockopt(fd,SOL_SOCKET, SO_REUSEADDR,1)");

exit(1)?;

}