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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) 2001-2003 The Open Group, All Rights Reserved --><title>umask</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="umask"></a> <a name="tag_04_152"></a><!-- umask --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2003 Edition<br>Copyright © 2001-2003 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_04_152_01"></a>NAME</h4><blockquote>umask - get or set the file mode creation mask</blockquote><h4><a name="tag_04_152_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><code><tt>umask</tt> <b>[</b><tt>-S</tt><b>][</b><i>mask</i><b>]</b></code></p></blockquote><h4><a name="tag_04_152_03"></a>DESCRIPTION</h4><blockquote><p>The <i>umask</i> utility shall set the file mode creation mask of the current shell execution environment (see <a href="xcu_chap02.html#tag_02_12"><i>Shell Execution Environment</i></a> ) to the value specified by the <i>mask</i> operand. This maskshall affect the initial value of the file permission bits of subsequently created files. If <i>umask</i> is called in a subshellor separate utility execution environment, such as one of the following:</p><pre><tt>(umask 002)nohup umask ...find . -exec umask ... \;</tt></pre><p>it shall not affect the file mode creation mask of the caller's environment.</p><p>If the <i>mask</i> operand is not specified, the <i>umask</i> utility shall write to standard output the value of the invokingprocess' file mode creation mask.</p></blockquote><h4><a name="tag_04_152_04"></a>OPTIONS</h4><blockquote><p>The <i>umask</i> utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap12.html#tag_12_02">Section 12.2, Utility Syntax Guidelines</a>.</p><p>The following option shall be supported:</p><dl compact><dt><b>-S</b></dt><dd>Produce symbolic output.</dd></dl><p>The default output style is unspecified, but shall be recognized on a subsequent invocation of <i>umask</i> on the same systemas a <i>mask</i> operand to restore the previous file mode creation mask.</p></blockquote><h4><a name="tag_04_152_05"></a>OPERANDS</h4><blockquote><p>The following operand shall be supported:</p><dl compact><dt><i>mask</i></dt><dd>A string specifying the new file mode creation mask. The string is treated in the same way as the <i>mode</i> operand describedin the EXTENDED DESCRIPTION section for <a href="../utilities/chmod.html"><i>chmod</i></a>. <p>For a <i>symbolic_mode</i> value, the new value of the file mode creation mask shall be the logical complement of the filepermission bits portion of the file mode specified by the <i>symbolic_mode</i> string.</p><p>In a <i>symbolic_mode</i> value, the permissions <i>op</i> characters <tt>'+'</tt> and <tt>'-'</tt> shall be interpretedrelative to the current file mode creation mask; <tt>'+'</tt> shall cause the bits for the indicated permissions to be cleared inthe mask; <tt>'-'</tt> shall cause the bits for the indicated permissions to be set in the mask.</p><p>The interpretation of <i>mode</i> values that specify file mode bits other than the file permission bits is unspecified.</p><p>In the octal integer form of <i>mode</i>, the specified bits are set in the file mode creation mask.</p><p>The file mode creation mask shall be set to the resulting numeric value.</p><p>The default output of a prior invocation of <i>umask</i> on the same system with no operand also shall be recognized as a<i>mask</i> operand.</p></dd></dl></blockquote><h4><a name="tag_04_152_06"></a>STDIN</h4><blockquote><p>Not used.</p></blockquote><h4><a name="tag_04_152_07"></a>INPUT FILES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_152_08"></a>ENVIRONMENT VARIABLES</h4><blockquote><p>The following environment variables shall affect the execution of <i>umask</i>:</p><dl compact><dt><i>LANG</i></dt><dd>Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume ofIEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap08.html#tag_08_02">Section 8.2, Internationalization Variables</a> forthe precedence of internationalization variables used to determine the values of locale categories.)</dd><dt><i>LC_ALL</i></dt><dd>If set to a non-empty string value, override the values of all the other internationalization variables.</dd><dt><i>LC_CTYPE</i></dt><dd>Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte asopposed to multi-byte characters in arguments).</dd><dt><i>LC_MESSAGES</i></dt><dd>Determine the locale that should be used to affect the format and contents of diagnostic messages written to standarderror.</dd><dt><i>NLSPATH</i></dt><dd><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">Determine the location of message catalogs for the processing of <i>LC_MESSAGES .</i> <img src="../images/opt-end.gif" alt="[Option End]" border="0"></dd></dl></blockquote><h4><a name="tag_04_152_09"></a>ASYNCHRONOUS EVENTS</h4><blockquote><p>Default.</p></blockquote><h4><a name="tag_04_152_10"></a>STDOUT</h4><blockquote><p>When the <i>mask</i> operand is not specified, the <i>umask</i> utility shall write a message to standard output that can laterbe used as a <i>umask</i> <i>mask</i> operand.</p><p>If <b>-S</b> is specified, the message shall be in the following format:</p><pre><tt>"u=%s,g=%s,o=%s\n", <</tt><i>owner permissions</i><tt>>, <</tt><i>group permissions</i><tt>>, <</tt><i>other permissions</i><tt>></tt></pre><p>where the three values shall be combinations of letters from the set { <i>r</i>, <i>w</i>, <i>x</i>}; the presence of a lettershall indicate that the corresponding bit is clear in the file mode creation mask.</p><p>If a <i>mask</i> operand is specified, there shall be no output written to standard output.</p></blockquote><h4><a name="tag_04_152_11"></a>STDERR</h4><blockquote><p>The standard error shall be used only for diagnostic messages.</p></blockquote><h4><a name="tag_04_152_12"></a>OUTPUT FILES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_152_13"></a>EXTENDED DESCRIPTION</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_152_14"></a>EXIT STATUS</h4><blockquote><p>The following exit values shall be returned:</p><dl compact><dt> 0</dt><dd>The file mode creation mask was successfully changed, or no <i>mask</i> operand was supplied.</dd><dt>>0</dt><dd>An error occurred.</dd></dl></blockquote><h4><a name="tag_04_152_15"></a>CONSEQUENCES OF ERRORS</h4><blockquote><p>Default.</p></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_04_152_16"></a>APPLICATION USAGE</h4><blockquote><p>Since <i>umask</i> affects the current shell execution environment, it is generally provided as a shell regular built-in.</p><p>In contrast to the negative permission logic provided by the file mode creation mask and the octal number form of the<i>mask</i> argument, the symbolic form of the <i>mask</i> argument specifies those permissions that are left alone.</p></blockquote><h4><a name="tag_04_152_17"></a>EXAMPLES</h4><blockquote><p>Either of the commands:</p><pre><tt>umask a=rx,ug+w<br>umask 002</tt></pre><p>sets the mode mask so that subsequently created files have their S_IWOTH bit cleared.</p><p>After setting the mode mask with either of the above commands, the <i>umask</i> command can be used to write out the currentvalue of the mode mask:</p><pre><b>$</b> <tt>umask</tt><b>0002</b></pre><p>(The output format is unspecified, but historical implementations use the octal integer mode format.)</p><pre><b>$</b> <tt>umask -S</tt><b>u=rwx,g=rwx,o=rx</b></pre><p>Either of these outputs can be used as the mask operand to a subsequent invocation of the <i>umask</i> utility.</p><p>Assuming the mode mask is set as above, the command:</p><pre><tt>umask g-w</tt></pre><p>sets the mode mask so that subsequently created files have their S_IWGRP and S_IWOTH bits cleared.</p><p>The command:</p><pre><tt>umask -- -w</tt></pre><p>sets the mode mask so that subsequently created files have all their write bits cleared. Note that <i>mask</i> operands<b>-r</b>, <b>-w</b>, <b>-x</b> or anything beginning with a hyphen, must be preceded by <tt>"--"</tt> to keep it from beinginterpreted as an option.</p></blockquote><h4><a name="tag_04_152_18"></a>RATIONALE</h4><blockquote><p>Since <i>umask</i> affects the current shell execution environment, it is generally provided as a shell regular built-in. If itis called in a subshell or separate utility execution environment, such as one of the following:</p><pre><tt>(umask 002)nohup umask ...find . -exec umask ... \;</tt></pre><p>it does not affect the file mode creation mask of the environment of the caller.</p><p>The description of the historical utility was modified to allow it to use the symbolic modes of <a href="../utilities/chmod.html"><i>chmod</i></a>. The <b>-s</b> option used in early proposals was changed to <b>-S</b> because <b>-s</b>could be confused with a <i>symbolic_mode</i> form of mask referring to the S_ISUID and S_ISGID bits.</p><p>The default output style is implementation-defined to permit implementors to provide migration to the new symbolic style at thetime most appropriate to their users. A <b>-o</b> flag to force octal mode output was omitted because the octal mode may not besufficient to specify all of the information that may be present in the file mode creation mask when more secure file accesspermission checks are implemented.</p><p>It has been suggested that trusted systems developers might appreciate ameliorating the requirement that the mode mask"affects" the file access permissions, since it seems access control lists might replace the mode mask to some degree. Thewording has been changed to say that it affects the file permission bits, and it leaves the details of the behavior of how theyaffect the file access permissions to the description in the System Interfaces volume of IEEE Std 1003.1-2001.</p></blockquote><h4><a name="tag_04_152_19"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_152_20"></a>SEE ALSO</h4><blockquote><p><a href="xcu_chap02.html#tag_02"><i>Shell Command Language</i></a> , <a href="chmod.html"><i>chmod</i></a> , the SystemInterfaces volume of IEEE Std 1003.1-2001, <a href="../functions/umask.html"><i>umask</i>()</a></p></blockquote><h4><a name="tag_04_152_21"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 2.</p></blockquote><h4><a name="tag_04_152_22"></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 octal mode is supported.</p></li></ul></blockquote><div class="box"><em>End of informative text.</em></div><hr><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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