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| <!-- %MENU% A more complicated IPC mechanism, with networking support --> |
| <h2 class="chapter">16 Sockets</h2> |
| |
| <p>This chapter describes the GNU facilities for interprocess |
| communication using sockets. |
| |
| <p><a name="index-socket-1630"></a><a name="index-interprocess-communication_002c-with-sockets-1631"></a>A <dfn>socket</dfn> is a generalized interprocess communication channel. |
| Like a pipe, a socket is represented as a file descriptor. Unlike pipes |
| sockets support communication between unrelated processes, and even |
| between processes running on different machines that communicate over a |
| network. Sockets are the primary means of communicating with other |
| machines; <code>telnet</code>, <code>rlogin</code>, <code>ftp</code>, <code>talk</code> and the |
| other familiar network programs use sockets. |
| |
| <p>Not all operating systems support sockets. In the GNU library, the |
| header file <samp><span class="file">sys/socket.h</span></samp> exists regardless of the operating |
| system, and the socket functions always exist, but if the system does |
| not really support sockets these functions always fail. |
| |
| <p><strong>Incomplete:</strong> We do not currently document the facilities for |
| broadcast messages or for configuring Internet interfaces. The |
| reentrant functions and some newer functions that are related to IPv6 |
| aren't documented either so far. |
| |
| <ul class="menu"> |
| <li><a accesskey="1" href="Socket-Concepts.html#Socket-Concepts">Socket Concepts</a>: Basic concepts you need to know about. |
| <li><a accesskey="2" href="Communication-Styles.html#Communication-Styles">Communication Styles</a>: Stream communication, datagrams and other styles. |
| <li><a accesskey="3" href="Socket-Addresses.html#Socket-Addresses">Socket Addresses</a>: How socket names (``addresses'') work. |
| <li><a accesskey="4" href="Interface-Naming.html#Interface-Naming">Interface Naming</a>: Identifying specific network interfaces. |
| <li><a accesskey="5" href="Local-Namespace.html#Local-Namespace">Local Namespace</a>: Details about the local namespace. |
| <li><a accesskey="6" href="Internet-Namespace.html#Internet-Namespace">Internet Namespace</a>: Details about the Internet namespace. |
| <li><a accesskey="7" href="Misc-Namespaces.html#Misc-Namespaces">Misc Namespaces</a>: Other namespaces not documented fully here. |
| <li><a accesskey="8" href="Open_002fClose-Sockets.html#Open_002fClose-Sockets">Open/Close Sockets</a>: Creating sockets and destroying them. |
| <li><a accesskey="9" href="Connections.html#Connections">Connections</a>: Operations on sockets with connection state. |
| <li><a href="Datagrams.html#Datagrams">Datagrams</a>: Operations on datagram sockets. |
| <li><a href="Inetd.html#Inetd">Inetd</a>: Inetd is a daemon that starts servers on request. |
| The most convenient way to write a server |
| is to make it work with Inetd. |
| <li><a href="Socket-Options.html#Socket-Options">Socket Options</a>: Miscellaneous low-level socket options. |
| <li><a href="Networks-Database.html#Networks-Database">Networks Database</a>: Accessing the database of network names. |
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