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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>nice</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="nice"></a> <a name="tag_04_92"></a><!-- nice --> <!--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_92_01"></a>NAME</h4><blockquote>nice - invoke a utility with an altered nice value</blockquote><h4><a name="tag_04_92_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><div class="box"><code><tt><sup>[<a href="javascript:open_code('UP')">UP</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> nice</tt> <b>[</b><tt>-n</tt> <i>increment</i><b>]</b> <i>utility</i><b>[</b><i>argument</i><tt>...</tt><b>]</b><tt><img src="../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div></blockquote><h4><a name="tag_04_92_03"></a>DESCRIPTION</h4><blockquote><p>The <i>nice</i> utility shall invoke a utility, requesting that it be run with a different nice value (see the Base Definitionsvolume of IEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap03.html#tag_03_239">Section 3.239, Nice Value</a>). With nooptions and only if the user has appropriate privileges, the executed utility shall be run with a nice value that is someimplementation-defined quantity less than or equal to the nice value of the current process. If the user lacks appropriateprivileges to affect the nice value in the requested manner, the <i>nice</i> utility shall not affect the nice value; in this case,a warning message may be written to standard error, but this shall not prevent the invocation of <i>utility</i> or affect the exitstatus.</p></blockquote><h4><a name="tag_04_92_04"></a>OPTIONS</h4><blockquote><p>The <i>nice</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 is supported:</p><dl compact><dt><b>-n </b> <i>increment</i></dt><dd>A positive or negative decimal integer which shall have the same effect on the execution of the utility as if the utility hadcalled the <a href="../functions/nice.html"><i>nice</i>()</a> function with the numeric value of the <i>increment</i>option-argument.</dd></dl></blockquote><h4><a name="tag_04_92_05"></a>OPERANDS</h4><blockquote><p>The following operands shall be supported:</p><dl compact><dt><i>utility</i></dt><dd>The name of a utility that is to be invoked. If the <i>utility</i> operand names any of the special built-in utilities in <ahref="xcu_chap02.html#tag_02_14"><i>Special Built-In Utilities</i></a> , the results are undefined.</dd><dt><i>argument</i></dt><dd>Any string to be supplied as an argument when invoking the utility named by the <i>utility</i> operand.</dd></dl></blockquote><h4><a name="tag_04_92_06"></a>STDIN</h4><blockquote><p>Not used.</p></blockquote><h4><a name="tag_04_92_07"></a>INPUT FILES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_92_08"></a>ENVIRONMENT VARIABLES</h4><blockquote><p>The following environment variables shall affect the execution of <i>nice</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><dt><i>PATH</i></dt><dd>Determine the search path used to locate the utility to be invoked. See the Base Definitions volume ofIEEE Std 1003.1-2001, <a href="../basedefs/xbd_chap08.html">Chapter 8, Environment Variables</a>.</dd></dl></blockquote><h4><a name="tag_04_92_09"></a>ASYNCHRONOUS EVENTS</h4><blockquote><p>Default.</p></blockquote><h4><a name="tag_04_92_10"></a>STDOUT</h4><blockquote><p>Not used.</p></blockquote><h4><a name="tag_04_92_11"></a>STDERR</h4><blockquote><p>The standard error shall be used only for diagnostic messages.</p></blockquote><h4><a name="tag_04_92_12"></a>OUTPUT FILES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_92_13"></a>EXTENDED DESCRIPTION</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_92_14"></a>EXIT STATUS</h4><blockquote><p>If <i>utility</i> is invoked, the exit status of <i>nice</i> shall be the exit status of <i>utility</i>; otherwise, the<i>nice</i> utility shall exit with one of the following values:</p><dl compact><dt>1-125</dt><dd>An error occurred in the <i>nice</i> utility.</dd><dt> 126</dt><dd>The utility specified by <i>utility</i> was found but could not be invoked.</dd><dt> 127</dt><dd>The utility specified by <i>utility</i> could not be found.</dd></dl></blockquote><h4><a name="tag_04_92_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_92_16"></a>APPLICATION USAGE</h4><blockquote><p>The only guaranteed portable uses of this utility are:</p><dl compact><dt><i>nice utility</i></dt><dd><br>Run <i>utility</i> with the default lower nice value.</dd><dt><i>nice </i> <b>-n </b> <<i>positive integer</i>><i> utility</i></dt><dd><br>Run <i>utility</i> with a lower nice value.</dd></dl><p>On some implementations they have no discernible effect on the invoked utility and on some others they are exactlyequivalent.</p><p>Historical systems have frequently supported the <<i>positive integer</i>> up to 20. Since there is no error penaltyassociated with guessing a number that is too high, users without access to the system conformance document (to see what limits areactually in place) could use the historical 1 to 20 range or attempt to use very large numbers if the job should be truly lowpriority.</p><p>The nice value of a process can be displayed using the command:</p><pre><tt>ps -o nice</tt></pre><p>The <a href="../utilities/command.html"><i>command</i></a>, <a href="../utilities/env.html"><i>env</i></a>, <i>nice</i>, <ahref="../utilities/nohup.html"><i>nohup</i></a>, <a href="../utilities/time.html"><i>time</i></a>, and <a href="../utilities/xargs.html"><i>xargs</i></a> utilities have been specified to use exit code 127 if an error occurs so thatapplications can distinguish "failure to find a utility" from "invoked utility exited with an error indication". The value 127was chosen because it is not commonly used for other meanings; most utilities use small values for "normal error conditions" andthe values above 128 can be confused with termination due to receipt of a signal. The value 126 was chosen in a similar manner toindicate that the utility could be found, but not invoked. Some scripts produce meaningful error messages differentiating the 126and 127 cases. The distinction between exit codes 126 and 127 is based on KornShell practice that uses 127 when all attempts to<i>exec</i> the utility fail with [ENOENT], and uses 126 when any attempt to <i>exec</i> the utility fails for any otherreason.</p></blockquote><h4><a name="tag_04_92_17"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_92_18"></a>RATIONALE</h4><blockquote><p>Due to the text about the limits of the nice value being implementation-defined, <i>nice</i> is not actually required to changethe nice value of the executed command; the limits could be zero differences from the system default, although the implementor isrequired to document this fact in the conformance document.</p><p>The 4.3 BSD version of <i>nice</i> does not check whether <i>increment</i> is a valid decimal integer. The command <i>nice</i><b>-x</b> <i>utility</i>, for example, would be treated the same as the command <i>nice</i> <b>--1</b> <i>utility</i>. If the userdoes not have appropriate privileges, this results in a "permission denied" error. This is considered a bug.</p><p>When a user without appropriate privileges gives a negative <i>increment</i>, System V treats it like the command <i>nice</i><b>-0</b> <i>utility</i>, while 4.3 BSD writes a "permission denied" message and does not run the utility. Neither was consideredclearly superior, so the behavior was left unspecified.</p><p>The C shell has a built-in version of <i>nice</i> that has a different interface from the one described in this volume ofIEEE Std 1003.1-2001.</p><p>The term "utility" is used, rather than "command", to highlight the fact that shell compound commands, pipelines, and so on,cannot be used. Special built-ins also cannot be used. However, "utility" includes user application programs and shell scripts,not just utilities defined in this volume of IEEE Std 1003.1-2001.</p><p>Historical implementations of <i>nice</i> provide a nice value range of 40 or 41 discrete steps, with the default nice valuebeing the midpoint of that range. By default, they lower the nice value of the executed utility by 10.</p><p>Some historical documentation states that the <i>increment</i> value must be within a fixed range. This is misleading; the valid<i>increment</i> values on any invocation are determined by the current process nice value, which is not always the default.</p><p>The definition of nice value is not intended to suggest that all processes in a system have priorities that are comparable.Scheduling policy extensions such as the realtime priorities in the System Interfaces volume of IEEE Std 1003.1-2001 makethe notion of a single underlying priority for all scheduling policies problematic. Some implementations may implement the<i>nice</i>-related features to affect all processes on the system, others to affect just the general time-sharing activitiesimplied by this volume of IEEE Std 1003.1-2001, and others may have no effect at all. Because of the use of"implementation-defined" in <i>nice</i> and <a href="../utilities/renice.html"><i>renice</i></a>, a wide range of implementationstrategies are possible.</p></blockquote><h4><a name="tag_04_92_19"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_92_20"></a>SEE ALSO</h4><blockquote><p><a href="xcu_chap02.html#tag_02"><i>Shell Command Language</i></a> , <a href="renice.html"><i>renice</i></a> , the SystemInterfaces volume of IEEE Std 1003.1-2001, <a href="../functions/nice.html"><i>nice</i>()</a></p></blockquote><h4><a name="tag_04_92_21"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 4.</p></blockquote><h4><a name="tag_04_92_22"></a>Issue 6</h4><blockquote><p>This utility is marked as part of the User Portability Utilities option.</p><p>The obsolescent SYNOPSIS is removed.</p></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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