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