Who is this FAQ for?

Unix Socket FAQ for Network programming

Who is this FAQ for?

This FAQ is for C programmers in the Unix environment. It is not intended for WinSock programmers, or for Perl, Java, etc. I have nothing against Windows or Perl, but I had to limit the scope of the FAQ for the first draft. In the future, I would really like to provide examples for Perl, Java, and maybe others. For now though I will concentrate on correctness and completeness for C.

This version of the FAQ will only cover sockets of the AF_INET family, since this is their most common use. Coverage of other types of sockets may be added later.

by Vic Metcalfe

(Continued on next question...)

Other Interview Questions

• Who is this FAQ for?
• What are Sockets?
• How do Sockets Work?
• How can I tell when a socket is closed on the other end?
• What's with the second parameter in bind()?
• How do I get the port number for a given service?
• If bind() fails, what should I do with the socket descriptor?
• How do I properly close a socket?
• When should I use shutdown()?
• What is the difference between close() and shutdown()?
• Code Sample: a very simple client process.
• Explain the TIME_WAIT state.
• Why does it take so long to detect that the peer died?
• What are the pros/cons of select(), non-blocking I/O and SIGIO?
• Why do I get EPROTO from read()?
• How can I force a socket to send the data in its buffer?
• Where can a get a library for programming sockets?
• How come select says there is data, but read returns zero?
• Whats the difference between select() and poll()?
• How do I send [this] over a socket?
• How do I use TCP_NODELAY?
• What exactly does the Nagle algorithm do?
• What is the difference between read() and recv()?
• Is there any advantage to handling the signal, rather than just ignoring it and checking for the EPIPE error? Are there any useful parameters passed to the signal catching function?
• After the chroot(), calls to socket() are failing. Why?
• Why do I keep getting EINTR from the socket calls?
• When will my application receive SIGPIPE?
• What are socket exceptions? What is out-of-band data?
• How can I find the full hostname (FQDN) of the system I'm running on?
• How do I convert a string into an internet address?
• How can my client work through a firewall/proxy server?
• Why does connect() succeed even before my server did an accept()?
• Why do I sometimes lose a server's address when using more than one server?
• How can I set the timeout for the connect() system call?
• system choose one for me on the connect() call? Should I bind() a port number in my client program, or let the
• Why do I get "connection refused" when the server isn't running?
• over the socket ? Is there a way to have a dynamic buffer ? What does one do when one does not know how much information is com- ming
• How come I get "address already in use" from bind()?
• Why don't my sockets close?
• How can I make my server a daemon?
• How can I listen on more than one port at a time?
• What exactly does SO_REUSEADDR do?
• What exactly does SO_LINGER do?
• What exactly does SO_KEEPALIVE do?
• How can I bind() to a port number < 1024?
• How do I get my server to find out the client's address / host- name?
• How should I choose a port number for my server?
• What is the difference between SO_REUSEADDR and SO_REUSEPORT?
• How can I write a multi-homed server?
• How can I read only one character at a time?
• I'm trying to exec() a program from my server, and attach my socket's IO to it, but I'm not getting all the data across. Why?
• When should I use UDP instead of TCP?
• What is the difference between "connected" and "unconnected" sockets?
• of the socket? Does doing a connect() call affect the receive behaviour
• How can I read ICMP errors from "connected" UDP sockets?
• How can I be sure that a UDP message is received?
• How can I be sure that UDP messages are received in order?
• How often should I re-transmit un-acknowleged messages?
• How come only the first part of my datagram is getting through?
• Why does the socket's buffer fill up sooner than expected?
• How would I put my socket in non-blocking mode?
• How can I put a timeout on connect()?