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| <h4 class="subsection">16.5.1 Local Namespace Concepts</h4> |
| |
| <p>In the local namespace socket addresses are file names. You can specify |
| any file name you want as the address of the socket, but you must have |
| write permission on the directory containing it. |
| <!-- XXX The following was said to be wrong. --> |
| <!-- In order to connect to a socket you must have read permission for it. --> |
| It's common to put these files in the <samp><span class="file">/tmp</span></samp> directory. |
| |
| <p>One peculiarity of the local namespace is that the name is only used |
| when opening the connection; once open the address is not meaningful and |
| may not exist. |
| |
| <p>Another peculiarity is that you cannot connect to such a socket from |
| another machine–not even if the other machine shares the file system |
| which contains the name of the socket. You can see the socket in a |
| directory listing, but connecting to it never succeeds. Some programs |
| take advantage of this, such as by asking the client to send its own |
| process ID, and using the process IDs to distinguish between clients. |
| However, we recommend you not use this method in protocols you design, |
| as we might someday permit connections from other machines that mount |
| the same file systems. Instead, send each new client an identifying |
| number if you want it to have one. |
| |
| <p>After you close a socket in the local namespace, you should delete the |
| file name from the file system. Use <code>unlink</code> or <code>remove</code> to |
| do this; see <a href="Deleting-Files.html#Deleting-Files">Deleting Files</a>. |
| |
| <p>The local namespace supports just one protocol for any communication |
| style; it is protocol number <code>0</code>. |
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