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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>chmod</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="chmod"></a> <a name="tag_03_70"></a><!-- chmod --> <!--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_70_01"></a>NAME</h4><blockquote>chmod - change mode of a file</blockquote><h4><a name="tag_03_70_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><code><tt>#include <<a href="../basedefs/sys/stat.h.html">sys/stat.h</a>><br><br> int chmod(const char *</tt><i>path</i><tt>, mode_t</tt> <i>mode</i><tt>);<br></tt></code></p></blockquote><h4><a name="tag_03_70_03"></a>DESCRIPTION</h4><blockquote><p>The <i>chmod</i>() function shall change S_ISUID, S_ISGID, <sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> S_ISVTX, <img src="../images/opt-end.gif" alt="[Option End]"border="0"> and the file permission bits of the file named by the pathname pointed to by the <i>path</i> argument to thecorresponding bits in the <i>mode</i> argument. The application shall ensure that the effective user ID of the process matches theowner of the file or the process has appropriate privileges in order to do this.</p><p>S_ISUID, S_ISGID, <sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> S_ISVTX, <img src="../images/opt-end.gif" alt="[Option End]" border="0"> and the file permissionbits are described in <a href="../basedefs/sys/stat.h.html"><i><sys/stat.h></i></a>.</p><p>If the calling process does not have appropriate privileges, and if the group ID of the file does not match the effective groupID or one of the supplementary group IDs and if the file is a regular file, bit S_ISGID (set-group-ID on execution) in the file'smode shall be cleared upon successful return from <i>chmod</i>().</p><p>Additional implementation-defined restrictions may cause the S_ISUID and S_ISGID bits in <i>mode</i> to be ignored.</p><p>The effect on file descriptors for files open at the time of a call to <i>chmod</i>() is implementation-defined.</p><p>Upon successful completion, <i>chmod</i>() shall mark for update the <i>st_ctime</i> field of the file.</p></blockquote><h4><a name="tag_03_70_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, no change to the file mode occurs.</p></blockquote><h4><a name="tag_03_70_05"></a>ERRORS</h4><blockquote><p>The <i>chmod</i>() function shall fail if:</p><dl compact><dt>[EACCES]</dt><dd>Search permission is denied on a component of the path prefix.</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>[ENOTDIR]</dt><dd>A component of the path prefix is not a directory.</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>[EPERM]</dt><dd>The effective user ID does not match the owner of the file and the process does not have appropriate privileges.</dd><dt>[EROFS]</dt><dd>The named file resides on a read-only file system.</dd></dl><p>The <i>chmod</i>() function may fail if:</p><dl compact><dt>[EINTR]</dt><dd>A signal was caught during execution of the function.</dd><dt>[EINVAL]</dt><dd>The value of the <i>mode</i> argument is invalid.</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 pathnamestrings exceeded {PATH_MAX}.</dd></dl></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_70_06"></a>EXAMPLES</h4><blockquote><h5><a name="tag_03_70_06_01"></a>Setting Read Permissions for User, Group, and Others</h5><p>The following example sets read permissions for the owner, group, and others.</p><pre><tt>#include <sys/stat.h><br>const char *path;...chmod(path, S_IRUSR|S_IRGRP|S_IROTH);</tt></pre><h5><a name="tag_03_70_06_02"></a>Setting Read, Write, and Execute Permissions for the Owner Only</h5><p>The following example sets read, write, and execute permissions for the owner, and no permissions for group and others.</p><pre><tt>#include <sys/stat.h><br>const char *path;...chmod(path, S_IRWXU);</tt></pre><h5><a name="tag_03_70_06_03"></a>Setting Different Permissions for Owner, Group, and Other</h5><p>The following example sets owner permissions for CHANGEFILE to read, write, and execute, group permissions to read and execute,and other permissions to read.</p><pre><tt>#include <sys/stat.h><br>#define CHANGEFILE "/etc/myfile"...chmod(CHANGEFILE, S_IRWXU|S_IRGRP|S_IXGRP|S_IROTH);</tt></pre><h5><a name="tag_03_70_06_04"></a>Setting and Checking File Permissions</h5><p>The following example sets the file permission bits for a file named <b>/home/cnd/mod1</b>, then calls the <a href="../functions/stat.html"><i>stat</i>()</a> function to verify the permissions.</p><pre><tt>#include <sys/types.h>#include <sys/stat.h><br>int status;struct stat buffer...chmod("home/cnd/mod1", S_IRWXU|S_IRWXG|S_IROTH|S_IWOTH);status = stat("home/cnd/mod1", &buffer;);</tt></pre></blockquote><h4><a name="tag_03_70_07"></a>APPLICATION USAGE</h4><blockquote><p>In order to ensure that the S_ISUID and S_ISGID bits are set, an application requiring this should use <a href="../functions/stat.html"><i>stat</i>()</a> after a successful <i>chmod</i>() to verify this.</p><p>Any file descriptors currently open by any process on the file could possibly become invalid if the mode of the file is changedto a value which would deny access to that process. One situation where this could occur is on a stateless file system. Thisbehavior will not occur in a conforming environment.</p></blockquote><h4><a name="tag_03_70_08"></a>RATIONALE</h4><blockquote><p>This volume of IEEE Std 1003.1-2001 specifies that the S_ISGID bit is cleared by <i>chmod</i>() on a regular fileunder certain conditions. This is specified on the assumption that regular files may be executed, and the system should preventusers from making executable <a href="../functions/setgid.html"><i>setgid</i>()</a> files perform with privileges that the callerdoes not have. On implementations that support execution of other file types, the S_ISGID bit should be cleared for those filetypes under the same circumstances.</p><p>Implementations that use the S_ISUID bit to indicate some other function (for example, mandatory record locking) onnon-executable files need not clear this bit on writing. They should clear the bit for executable files and any other cases wherethe bit grants special powers to processes that change the file contents. Similar comments apply to the S_ISGID bit.</p></blockquote><h4><a name="tag_03_70_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_70_10"></a>SEE ALSO</h4><blockquote><p><a href="chown.html"><i>chown</i>()</a>, <a href="mkdir.html"><i>mkdir</i>()</a>, <a href="mkfifo.html"><i>mkfifo</i>()</a>,<a href="open.html"><i>open</i>()</a>, <a href="stat.html"><i>stat</i>()</a>, <a href="statvfs.html"><i>statvfs</i>()</a>, theBase Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/sys/stat.h.html"><i><sys/stat.h></i></a>, <ahref="../basedefs/sys/types.h.html"><i><sys/types.h></i></a></p></blockquote><h4><a name="tag_03_70_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_70_12"></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>The requirement to include <a href="../basedefs/sys/types.h.html"><i><sys/types.h></i></a> has been removed. Although <ahref="../basedefs/sys/types.h.html"><i><sys/types.h></i></a> was required for conforming implementations of previous POSIXspecifications, it was not required for UNIX applications.</p></li><li><p>The [EINVAL] and [EINTR] optional error conditions are added.</p></li><li><p>A second [ENAMETOOLONG] is added as an optional error condition.</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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