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| <h3 class="section">14.4 Hard Links</h3> |
| |
| <p><a name="index-hard-link-1456"></a><a name="index-link_002c-hard-1457"></a><a name="index-multiple-names-for-one-file-1458"></a><a name="index-file-names_002c-multiple-1459"></a> |
| In POSIX systems, one file can have many names at the same time. All of |
| the names are equally real, and no one of them is preferred to the |
| others. |
| |
| <p>To add a name to a file, use the <code>link</code> function. (The new name is |
| also called a <dfn>hard link</dfn> to the file.) Creating a new link to a |
| file does not copy the contents of the file; it simply makes a new name |
| by which the file can be known, in addition to the file's existing name |
| or names. |
| |
| <p>One file can have names in several directories, so the organization |
| of the file system is not a strict hierarchy or tree. |
| |
| <p>In most implementations, it is not possible to have hard links to the |
| same file in multiple file systems. <code>link</code> reports an error if you |
| try to make a hard link to the file from another file system when this |
| cannot be done. |
| |
| <p>The prototype for the <code>link</code> function is declared in the header |
| file <samp><span class="file">unistd.h</span></samp>. |
| <a name="index-unistd_002eh-1460"></a> |
| <!-- unistd.h --> |
| <!-- POSIX.1 --> |
| |
| <div class="defun"> |
| — Function: int <b>link</b> (<var>const char *oldname, const char *newname</var>)<var><a name="index-link-1461"></a></var><br> |
| <blockquote><p>The <code>link</code> function makes a new link to the existing file named by |
| <var>oldname</var>, under the new name <var>newname</var>. |
| |
| <p>This function returns a value of <code>0</code> if it is successful and |
| <code>-1</code> on failure. In addition to the usual file name errors |
| (see <a href="File-Name-Errors.html#File-Name-Errors">File Name Errors</a>) for both <var>oldname</var> and <var>newname</var>, the |
| following <code>errno</code> error conditions are defined for this function: |
| |
| <dl> |
| <dt><code>EACCES</code><dd>You are not allowed to write to the directory in which the new link is |
| to be written. |
| |
| <br><dt><code>EEXIST</code><dd>There is already a file named <var>newname</var>. If you want to replace |
| this link with a new link, you must remove the old link explicitly first. |
| |
| <br><dt><code>EMLINK</code><dd>There are already too many links to the file named by <var>oldname</var>. |
| (The maximum number of links to a file is <code>LINK_MAX</code><!-- /@w -->; see |
| <a href="Limits-for-Files.html#Limits-for-Files">Limits for Files</a>.) |
| |
| <br><dt><code>ENOENT</code><dd>The file named by <var>oldname</var> doesn't exist. You can't make a link to |
| a file that doesn't exist. |
| |
| <br><dt><code>ENOSPC</code><dd>The directory or file system that would contain the new link is full |
| and cannot be extended. |
| |
| <br><dt><code>EPERM</code><dd>In the GNU system and some others, you cannot make links to directories. |
| Many systems allow only privileged users to do so. This error |
| is used to report the problem. |
| |
| <br><dt><code>EROFS</code><dd>The directory containing the new link can't be modified because it's on |
| a read-only file system. |
| |
| <br><dt><code>EXDEV</code><dd>The directory specified in <var>newname</var> is on a different file system |
| than the existing file. |
| |
| <br><dt><code>EIO</code><dd>A hardware error occurred while trying to read or write the to filesystem. |
| </dl> |
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