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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta name="generator" content="HTML Tidy, see www.w3.org"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 --><!-- Copyright (c) 2001-2004 IEEE and The Open Group, All Rights Reserved --><title>unlink</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="unlink"></a> <a name="tag_03_802"></a><!-- unlink --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2004 Edition<br>Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_03_802_01"></a>NAME</h4><blockquote>unlink - remove a directory entry</blockquote><h4><a name="tag_03_802_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><code><tt>#include <<a href="../basedefs/unistd.h.html">unistd.h</a>><br><br> int unlink(const char *</tt><i>path</i><tt>);<br></tt></code></p></blockquote><h4><a name="tag_03_802_03"></a>DESCRIPTION</h4><blockquote><p>The <i>unlink</i>() function shall remove a link to a file. If <i>path</i> names a symbolic link, <i>unlink</i>() shall removethe symbolic link named by <i>path</i> and shall not affect any file or directory named by the contents of the symbolic link.Otherwise, <i>unlink</i>() shall remove the link named by the pathname pointed to by <i>path</i> and shall decrement the link countof the file referenced by the link.</p><p>When the file's link count becomes 0 and no process has the file open, the space occupied by the file shall be freed and thefile shall no longer be accessible. If one or more processes have the file open when the last link is removed, the link shall beremoved before <i>unlink</i>() returns, but the removal of the file contents shall be postponed until all references to the fileare closed.</p><p>The <i>path</i> argument shall not name a directory unless the process has appropriate privileges and the implementationsupports using <i>unlink</i>() on directories.</p><p>Upon successful completion, <i>unlink</i>() shall mark for update the <i>st_ctime</i> and <i>st_mtime</i> fields of the parentdirectory. Also, if the file's link count is not 0, the <i>st_ctime</i> field of the file shall be marked for update.</p></blockquote><h4><a name="tag_03_802_04"></a>RETURN VALUE</h4><blockquote><p>Upon successful completion, 0 shall be returned. Otherwise, -1 shall be returned and <i>errno</i> set to indicate the error. If-1 is returned, the named file shall not be changed.</p></blockquote><h4><a name="tag_03_802_05"></a>ERRORS</h4><blockquote><p>The <i>unlink</i>() function shall fail and shall not unlink the file if:</p><dl compact><dt>[EACCES]</dt><dd>Search permission is denied for a component of the path prefix, or write permission is denied on the directory containing thedirectory entry to be removed.</dd><dt>[EBUSY]</dt><dd>The file named by the <i>path</i> argument cannot be unlinked because it is being used by the system or another process and theimplementation considers this an error.</dd><dt>[ELOOP]</dt><dd>A loop exists in symbolic links encountered during resolution of the <i>path</i> argument.</dd><dt>[ENAMETOOLONG]</dt><dd>The length of the <i>path</i> argument exceeds {PATH_MAX} or a pathname component is longer than {NAME_MAX}.</dd><dt>[ENOENT]</dt><dd>A component of <i>path</i> does not name an existing file or <i>path</i> is an empty string.</dd><dt>[ENOTDIR]</dt><dd>A component of the path prefix is not a directory.</dd><dt>[EPERM]</dt><dd>The file named by <i>path</i> is a directory, and either the calling process does not have appropriate privileges, or theimplementation prohibits using <i>unlink</i>() on directories.</dd><dt>[EPERM] or [EACCES]</dt><dd><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"><br>The S_ISVTX flag is set on the directory containing the file referred to by the <i>path</i> argument and the caller is not the fileowner, nor is the caller the directory owner, nor does the caller have appropriate privileges. <img src="../images/opt-end.gif"alt="[Option End]" border="0"></dd><dt>[EROFS]</dt><dd>The directory entry to be unlinked is part of a read-only file system.</dd></dl><p>The <i>unlink</i>() function may fail and not unlink the file if:</p><dl compact><dt>[EBUSY]</dt><dd><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">The file named by <i>path</i> is a named STREAM. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd><dt>[ELOOP]</dt><dd>More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the <i>path</i> argument.</dd><dt>[ENAMETOOLONG]</dt><dd>As a result of encountering a symbolic link in resolution of the <i>path</i> argument, the length of the substituted pathnamestring exceeded {PATH_MAX}.</dd><dt>[ETXTBSY]</dt><dd>The entry to be unlinked is the last directory entry to a pure procedure (shared text) file that is being executed.</dd></dl></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_802_06"></a>EXAMPLES</h4><blockquote><h5><a name="tag_03_802_06_01"></a>Removing a Link to a File</h5><p>The following example shows how to remove a link to a file named <b>/home/cnd/mod1</b> by removing the entry named<b>/modules/pass1</b>.</p><pre><tt>#include <unistd.h><br>char *path = "/modules/pass1";int status;...status = unlink(path);</tt></pre><h5><a name="tag_03_802_06_02"></a>Checking for an Error</h5><p>The following example fragment creates a temporary password lock file named <b>LOCKFILE</b>, which is defined as<b>/etc/ptmp</b>, and gets a file descriptor for it. If the file cannot be opened for writing, <i>unlink</i>() is used to removethe link between the file descriptor and <b>LOCKFILE</b>.</p><pre><tt>#include <sys/types.h>#include <stdio.h>#include <fcntl.h>#include <errno.h>#include <unistd.h>#include <sys/stat.h><br>#define LOCKFILE "/etc/ptmp"<br>int pfd; /* Integer for file descriptor returned by open call. */FILE *fpfd; /* File pointer for use in putpwent(). */.../* Open password Lock file. If it exists, this is an error. */if ((pfd = open(LOCKFILE, O_WRONLY| O_CREAT | O_EXCL, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)) == -1) { fprintf(stderr, "Cannot open /etc/ptmp. Try again later.\n"); exit(1);}<br>/* Lock file created; proceed with fdopen of lock file so that putpwent() can be used. */if ((fpfd = fdopen(pfd, "w")) == NULL) { close(pfd); unlink(LOCKFILE); exit(1);}</tt></pre><h5><a name="tag_03_802_06_03"></a>Replacing Files</h5><p>The following example fragment uses <i>unlink</i>() to discard links to files, so that they can be replaced with new versions ofthe files. The first call removes the link to <b>LOCKFILE</b> if an error occurs. Successive calls remove the links to<b>SAVEFILE</b> and <b>PASSWDFILE</b> so that new links can be created, then removes the link to <b>LOCKFILE</b> when it is nolonger needed.</p><pre><tt>#include <sys/types.h>#include <stdio.h>#include <fcntl.h>#include <errno.h>#include <unistd.h>#include <sys/stat.h><br>#define LOCKFILE "/etc/ptmp"#define PASSWDFILE "/etc/passwd"#define SAVEFILE "/etc/opasswd".../* If no change was made, assume error and leave passwd unchanged. */if (!valid_change) { fprintf(stderr, "Could not change password for user %s\n", user); unlink(LOCKFILE); exit(1);}<br>/* Change permissions on new password file. */chmod(LOCKFILE, S_IRUSR | S_IRGRP | S_IROTH);<br>/* Remove saved password file. */unlink(SAVEFILE);<br>/* Save current password file. */link(PASSWDFILE, SAVEFILE);<br>/* Remove current password file. */unlink(PASSWDFILE);<br>/* Save new password file as current password file. */link(LOCKFILE,PASSWDFILE);<br>/* Remove lock file. */unlink(LOCKFILE);<br>exit(0);</tt></pre></blockquote><h4><a name="tag_03_802_07"></a>APPLICATION USAGE</h4><blockquote><p>Applications should use <a href="../functions/rmdir.html"><i>rmdir</i>()</a> to remove a directory.</p></blockquote><h4><a name="tag_03_802_08"></a>RATIONALE</h4><blockquote><p>Unlinking a directory is restricted to the superuser in many historical implementations for reasons given in <a href="../functions/link.html"><i>link</i>()</a> (see also <a href="../functions/rename.html"><i>rename</i>()</a>).</p><p>The meaning of [EBUSY] in historical implementations is "mount point busy". Since this volume ofIEEE Std 1003.1-2001 does not cover the system administration concepts of mounting and unmounting, the description of theerror was changed to "resource busy". (This meaning is used by some device drivers when a second process tries to open anexclusive use device.) The wording is also intended to allow implementations to refuse to remove a directory if it is the root orcurrent working directory of any process.</p></blockquote><h4><a name="tag_03_802_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_802_10"></a>SEE ALSO</h4><blockquote><p><a href="close.html"><i>close</i>()</a>, <a href="link.html"><i>link</i>()</a>, <a href="remove.html"><i>remove</i>()</a>, <ahref="rmdir.html"><i>rmdir</i>()</a>, the Base Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/unistd.h.html"><i><unistd.h></i></a></p></blockquote><h4><a name="tag_03_802_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 1. Derived from Issue 1 of the SVID.</p></blockquote><h4><a name="tag_03_802_12"></a>Issue 5</h4><blockquote><p>The [EBUSY] error is added to the optional part of the ERRORS section.</p></blockquote><h4><a name="tag_03_802_13"></a>Issue 6</h4><blockquote><p>The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:</p><ul><li><p>In the DESCRIPTION, the effect is specified if <i>path</i> specifies a symbolic link.</p></li><li><p>The [ELOOP] mandatory error condition is added.</p></li><li><p>A second [ENAMETOOLONG] is added as an optional error condition.</p></li><li><p>The [ETXTBSY] optional error condition is added.</p></li></ul><p>The following changes were made to align with the IEEE P1003.1a draft standard:</p><ul><li><p>The [ELOOP] optional error condition is added.</p></li></ul><p>The DESCRIPTION is updated to avoid use of the term "must" for application requirements.</p></blockquote><div class="box"><em>End of informative text.</em></div><hr size="2" noshade><center><font size="2"><!--footer start-->UNIX ® is a registered Trademark of The Open Group.<br>POSIX ® is a registered Trademark of The IEEE.<br>[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href="../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>]</font></center><!--footer end--><hr size="2" noshade></body></html>⌨️ 快捷键说明
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