334 lines
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334 lines
13 KiB
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<title>newgrp</title>
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<basefont size="3"> <a name="newgrp"></a> <a name="tag_04_91"></a><!-- newgrp -->
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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_91_01"></a>NAME</h4>
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<blockquote>newgrp - change to a new group</blockquote>
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<h4><a name="tag_04_91_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<div class="box"><code><tt><sup>[<a href="javascript:open_code('UP')">UP</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> newgrp</tt> <b>[</b><tt>-l</tt><b>][</b><i>group</i><b>]</b><tt><img src="../images/opt-end.gif" alt=
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"[Option End]" border="0"></tt></code></div>
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</blockquote>
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<h4><a name="tag_04_91_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>newgrp</i> utility shall create a new shell execution environment with a new real and effective group identification. Of
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the attributes listed in <a href="xcu_chap02.html#tag_02_12"><i>Shell Execution Environment</i></a> , the new shell execution
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environment shall retain the working directory, file creation mask, and exported variables from the previous environment (that is,
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open files, traps, unexported variables, alias definitions, shell functions, and <a href=
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"../utilities/set.html"><i>set</i></a> options may be lost). All other aspects of the process environment that are
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preserved by the <i>exec</i> family of functions defined in the System Interfaces volume of IEEE Std 1003.1-2001 shall
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also be preserved by <i>newgrp</i>; whether other aspects are preserved is unspecified.</p>
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<p>A failure to assign the new group identifications (for example, for security or password-related reasons) shall not prevent the
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new shell execution environment from being created.</p>
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<p>The <i>newgrp</i> utility shall affect the supplemental groups for the process as follows:</p>
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<ul>
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<li>
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<p>On systems where the effective group ID is normally in the supplementary group list (or whenever the old effective group ID
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actually is in the supplementary group list):</p>
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<ul>
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<li>
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<p>If the new effective group ID is also in the supplementary group list, <i>newgrp</i> shall change the effective group ID.</p>
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</li>
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<li>
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<p>If the new effective group ID is not in the supplementary group list, <i>newgrp</i> shall add the new effective group ID to the
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list, if there is room to add it.</p>
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</li>
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</ul>
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</li>
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<li>
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<p>On systems where the effective group ID is not normally in the supplementary group list (or whenever the old effective group ID
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is not in the supplementary group list):</p>
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<ul>
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<li>
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<p>If the new effective group ID is in the supplementary group list, <i>newgrp</i> shall delete it.</p>
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</li>
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<li>
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<p>If the old effective group ID is not in the supplementary list, <i>newgrp</i> shall add it if there is room.</p>
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</li>
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</ul>
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</li>
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</ul>
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<basefont size="2">
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<dl>
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<dt><b>Note:</b></dt>
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<dd>The System Interfaces volume of IEEE Std 1003.1-2001 does not specify whether the effective group ID of a process is
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included in its supplementary group list.</dd>
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</dl>
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<basefont size="3">
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<p>With no operands, <i>newgrp</i> shall change the effective group back to the groups identified in the user's user entry, and
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shall set the list of supplementary groups to that set in the user's group database entries.</p>
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<p>If a password is required for the specified group, and the user is not listed as a member of that group in the group database,
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the user shall be prompted to enter the correct password for that group. If the user is listed as a member of that group, no
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password shall be requested. If no password is required for the specified group, it is implementation-defined whether users not
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listed as members of that group can change to that group. Whether or not a password is required, implementation-defined system
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accounting or security mechanisms may impose additional authorization restrictions that may cause <i>newgrp</i> to write a
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diagnostic message and suppress the changing of the group identification.</p>
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</blockquote>
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<h4><a name="tag_04_91_04"></a>OPTIONS</h4>
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<blockquote>
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<p>The <i>newgrp</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>-l</b></dt>
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<dd>(The letter ell.) Change the environment to what would be expected if the user actually logged in again.</dd>
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</dl>
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</blockquote>
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<h4><a name="tag_04_91_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>group</i></dt>
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<dd>A group name from the group database or a non-negative numeric group ID. Specifies the group ID to which the real and effective
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group IDs shall be set. If <i>group</i> is a non-negative numeric string and exists in the group database as a group name (see <a
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href="../functions/getgrnam.html"><i>getgrnam</i>()</a>), the numeric group ID associated with that group name shall be used as the
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group ID.</dd>
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</dl>
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</blockquote>
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<h4><a name="tag_04_91_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_91_07"></a>INPUT FILES</h4>
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<blockquote>
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<p>The file <b>/dev/tty</b> shall be used to read a single line of text for password checking, when one is required.</p>
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</blockquote>
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<h4><a name="tag_04_91_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>newgrp</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_91_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_91_10"></a>STDOUT</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_91_11"></a>STDERR</h4>
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<blockquote>
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<p>The standard error shall be used for diagnostic messages and a prompt string for a password, if one is required. Diagnostic
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messages may be written in cases where the exit status is not available. See the EXIT STATUS section.</p>
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</blockquote>
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<h4><a name="tag_04_91_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_91_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_91_14"></a>EXIT STATUS</h4>
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<blockquote>
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<p>If <i>newgrp</i> succeeds in creating a new shell execution environment, whether or not the group identification was changed
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successfully, the exit status shall be the exit status of the shell. Otherwise, the following exit value shall be returned:</p>
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<dl compact>
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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_91_15"></a>CONSEQUENCES OF ERRORS</h4>
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<blockquote>
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<p>The invoking shell may terminate.</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_91_16"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>There is no convenient way to enter a password into the group database. Use of group passwords is not encouraged, because by
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their very nature they encourage poor security practices. Group passwords may disappear in the future.</p>
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<p>A common implementation of <i>newgrp</i> is that the current shell uses <i>exec</i> to overlay itself with <i>newgrp</i>, which
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in turn overlays itself with a new shell after changing group. On some implementations, however, this may not occur and
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<i>newgrp</i> may be invoked as a subprocess.</p>
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<p>The <i>newgrp</i> command is intended only for use from an interactive terminal. It does not offer a useful interface for the
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support of applications.</p>
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<p>The exit status of <i>newgrp</i> is generally inapplicable. If <i>newgrp</i> is used in a script, in most cases it successfully
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invokes a new shell and the rest of the original shell script is bypassed when the new shell exits. Used interactively,
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<i>newgrp</i> displays diagnostic messages to indicate problems. But usage such as:</p>
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<pre>
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<tt>newgrp foo
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echo $?
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</tt>
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</pre>
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<p>is not useful because the new shell might not have access to any status <i>newgrp</i> may have generated (and most historical
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systems do not provide this status). A zero status echoed here does not necessarily indicate that the user has changed to the new
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group successfully. Following <i>newgrp</i> with the <a href="../utilities/id.html"><i>id</i></a> command provides a portable means
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of determining whether the group change was successful or not.</p>
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</blockquote>
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<h4><a name="tag_04_91_17"></a>EXAMPLES</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_91_18"></a>RATIONALE</h4>
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<blockquote>
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<p>Most historical implementations use one of the <i>exec</i> functions to implement the behavior of <i>newgrp</i>. Errors detected
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before the <i>exec</i> leave the environment unchanged, while errors detected after the <i>exec</i> leave the user in a changed
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environment. While it would be useful to have <i>newgrp</i> issue a diagnostic message to tell the user that the environment
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changed, it would be inappropriate to require this change to some historical implementations.</p>
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<p>The password mechanism is allowed in the group database, but how this would be implemented is not specified.</p>
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<p>The <i>newgrp</i> utility was retained in this volume of IEEE Std 1003.1-2001, even given the existence of the
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multiple group permissions feature in the System Interfaces volume of IEEE Std 1003.1-2001, for several reasons. First,
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in some implementations, the group ownership of a newly created file is determined by the group of the directory in which the file
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is created, as allowed by the System Interfaces volume of IEEE Std 1003.1-2001; on other implementations, the group
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ownership of a newly created file is determined by the effective group ID. On implementations of the latter type, <i>newgrp</i>
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allows files to be created with a specific group ownership. Finally, many implementations use the real group ID in accounting, and
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on such systems, <i>newgrp</i> allows the accounting identity of the user to be changed.</p>
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</blockquote>
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<h4><a name="tag_04_91_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_91_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="sh.html"><i>sh</i></a> , the System Interfaces
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volume of IEEE Std 1003.1-2001, <i>exec</i>, <a href="../functions/getgrnam.html"><i>getgrnam</i>()</a></p>
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</blockquote>
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<h4><a name="tag_04_91_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_91_22"></a>Issue 6</h4>
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<blockquote>
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<p>This utility is marked as part of the User Portability Utilities option.</p>
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<p>The obsolescent SYNOPSIS is removed.</p>
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<p>The text describing supplemental groups is no longer conditional on {NGROUPS_MAX} being greater than 1. This is because
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{NGROUPS_MAX} now has a minimum value of 8. This is a FIPS requirement.</p>
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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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<center><font size="2"><!--footer start-->
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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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[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href=
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"../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>
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