ASGAUR

About this FAQ This FAQ is maintained by Vic Metcalfe ( vic@acm.org ), with lots o

Who is this FAQ for? This FAQ is for C programmers in the Unix environment. It is

What are Sockets? Sockets are just like "worm holes" in science fiction. When thi

How do Sockets Work? The implementation is left up to the vendor of your particula

Where can I get source code for the book [book title]? Here is a list of the place

Where can I get more information? I keep a copy of the resources I know of on my s

How can I tell when a socket is closed on the other end? From Andrew Gierth ( andr

Why do I get EPROTO from read()? From Steve Rago ( sar@plc.com ): EPROTO mean

How can I force a socket to send the data in its buffer? From Richard Stevens ( rs

Where can a get a library for programming sockets? There is the Simple Sockets Lib

How come select says there is data, but read returns zero? The data that causes se

Whats the difference between select() and poll()? From Richard Stevens ( rstevens@

How do I send [this] over a socket? Anything other than single bytes of data will

How do I use TCP_NODELAY? First off, be sure you really want to use it in the firs

What exactly does the Nagle algorithm do? It groups together as much data as it ca

What is the difference between read() and recv()? From Andrew Gierth ( andrew@erle

I see that send()/write() can generate SIGPIPE checking for the EPIPE error? Are there an

What's with the second parameter in bind()? The man page shows it as "struct socka

After the chroot(), calls to socket() are failing From Andrew Gierth ( andrew@erlenstar.d

Why do I keep getting EINTR from the socket calls? This isn't really so much an er

When will my application receive SIGPIPE? From Richard Stevens ( rstevens@noao.edu

What are socket exceptions? What is out-of-band data? Unlike exceptions in C++, s

running on? How can I find the full hostname (FQDN) of the From Richard Stevens

How do I get the port number for a given service? Use the getservbyname() routine.

If bind() fails, what should I do with the socket descriptor? If you are exiting,

How do I properly close a socket? This question is usually asked by people who try

When should I use shutdown()? From Michael Hunter ( mphunter@qnx.com ): shutd

Please explain the TIME_WAIT state. Remember that TCP guarantees all data transmit

Why does it take so long to detect that the peer died? From Andrew Gierth ( andrew

What are the pros/cons of select(), non-blocking I/O and SIGIO? Using non-blocking

How do I convert a string into an internet address? If you are reading a host's ad

How can my client work through a firewall/proxy server? If you are running through

Why does connect() succeed even before my server did an From Andrew Gierth ( and

Why do I sometimes lose a server's address when using more than From Andrew Gier

How can I set the timeout for the connect() system call? From Richard Stevens ( rs

system choose one for me on the connect() call? Should I bind() From Andrew Gie

Why do I get "connection refused" when the server isn't running? The connect() cal

over the socket ? Is there a way to have a dynamic buffer ? ming This questio

How come I get "address already in use" from bind()? You get this when the address

How should I choose a port number for my server? The list of registered port assig

What is the difference between SO_REUSEADDR and SO_REUSEPORT? SO_REUSEADDR allows

How can I write a multi-homed server? The original question was actually from Shan

Writing Server Applications (TCP/SOCK_STREAM): How can I read only one character at a

I'm trying to exec() a program from my server, and attach my If the program you

Why don't my sockets close? When you issue the close() system call, you are closin

How can I make my server a daemon? There are two approaches you can take here. Th

How can I listen on more than one port at a time? The best way to do this is with

What exactly does SO_REUSEADDR do? This socket option tells the kernel that even i

What exactly does SO_LINGER do? On some unixes this does nothing. On others, it i

What exactly does SO_KEEPALIVE do? From Andrew Gierth ( andrew@erlenstar.demon.co.

How can I bind() to a port number < 1024? From Andrew Gierth ( andrew@erlenstar.de

How do I get my server to find out the client's address / host- From Andrew Gier

When should I use UDP instead of TCP? UDP is good for sending messages from one sy

What is the difference between "connected" and "unconnected" From Andrew Gierth

of the socket? Does doing a connect() call affect the receive From Richard Stev

How can I read ICMP errors from "connected" UDP sockets? If the target machine dis

How can I be sure that a UDP message is received? You have to design your protocol

How can I be sure that UDP messages are received in order? You can't. What you ca

How often should I re-transmit un-acknowleged messages? The simplest thing to do i

How come only the first part of my datagram is getting through? This has to do wit

Why does the socket's buffer fill up sooner than expected? From Paul W. Nelson ( n

How would I put my socket in non-blocking mode? From Andrew Gierth ( andrew@erlens

How can I put a timeout on connect()? Andrew Gierth ( andrew@erlenstar.demon.co.uk

Sample Source Code The sample source code is no longer included in the faq. To ge