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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>crontab</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="crontab"></a> <a name="tag_04_28"></a><!-- crontab --> <!--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_04_28_01"></a>NAME</h4><blockquote>crontab - schedule periodic background work</blockquote><h4><a name="tag_04_28_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"> crontab</tt> <b>[</b><i>file</i><b>]</b><tt><br><br>crontab</tt> <b>[</b> <tt>-e | -l | -r</tt> <b>]</b><tt><img src="../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div><tt><br></tt></blockquote><h4><a name="tag_04_28_03"></a>DESCRIPTION</h4><blockquote><p>The <i>crontab</i> utility shall create, replace, or edit a user's crontab entry; a crontab entry is a list of commands and thetimes at which they shall be executed. The new crontab entry can be input by specifying <i>file</i> or input from standard input ifno <i>file</i> operand is specified, or by using an editor, if <b>-e</b> is specified.</p><p>Upon execution of a command from a crontab entry, the implementation shall supply a default environment, defining at least thefollowing environment variables:</p><dl compact><dt><i>HOME</i></dt><dd>A pathname of the user's home directory.</dd><dt><i>LOGNAME</i></dt><dd>The user's login name.</dd><dt><i>PATH</i></dt><dd>A string representing a search path guaranteed to find all of the standard utilities.</dd><dt><i>SHELL</i></dt><dd>A pathname of the command interpreter. When <i>crontab</i> is invoked as specified by this volume ofIEEE Std 1003.1-2001, the value shall be a pathname for <a href="../utilities/sh.html"><i>sh</i></a>.</dd></dl><p>The values of these variables when <i>crontab</i> is invoked as specified by this volume of IEEE Std 1003.1-2001 shallnot affect the default values provided when the scheduled command is run.</p><p>If standard output and standard error are not redirected by commands executed from the crontab entry, any generated output orerrors shall be mailed, via an implementation-defined method, to the user.</p><p><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">Users shall be permitted to use <i>crontab</i> if their names appear in the file <b>/usr/lib/cron/cron.allow</b>. If that file doesnot exist, the file <b>/usr/lib/cron/cron.deny</b> shall be checked to determine whether the user shall be denied access to<i>crontab</i>. If neither file exists, only a process with appropriate privileges shall be allowed to submit a job. If only<b>cron.deny</b> exists and is empty, global usage shall be permitted. The <b>cron.allow</b> and <b>cron.deny</b> files shallconsist of one user name per line. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p></blockquote><h4><a name="tag_04_28_04"></a>OPTIONS</h4><blockquote><p>The <i>crontab</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 options shall be supported:</p><dl compact><dt><b>-e</b></dt><dd>Edit a copy of the invoking user's crontab entry, or create an empty entry to edit if the crontab entry does not exist. Whenediting is complete, the entry shall be installed as the user's crontab entry.</dd><dt><b>-l</b></dt><dd>(The letter ell.) List the invoking user's crontab entry.</dd><dt><b>-r</b></dt><dd>Remove the invoking user's crontab entry.</dd></dl></blockquote><h4><a name="tag_04_28_05"></a>OPERANDS</h4><blockquote><p>The following operand shall be supported:</p><dl compact><dt><i>file</i></dt><dd>The pathname of a file that contains specifications, in the format defined in the INPUT FILES section, for crontabentries.</dd></dl></blockquote><h4><a name="tag_04_28_06"></a>STDIN</h4><blockquote><p>See the INPUT FILES section.</p></blockquote><h4><a name="tag_04_28_07"></a>INPUT FILES</h4><blockquote><p>In the POSIX locale, the user or application shall ensure that a crontab entry is a text file consisting of lines of six fieldseach. The fields shall be separated by <blank>s. The first five fields shall be integer patterns that specify thefollowing:</p><ol><li><p>Minute [0,59]</p></li><li><p>Hour [0,23]</p></li><li><p>Day of the month [1,31]</p></li><li><p>Month of the year [1,12]</p></li><li><p>Day of the week ([0,6] with 0=Sunday)</p></li></ol><p>Each of these patterns can be either an asterisk (meaning all valid values), an element, or a list of elements separated bycommas. An element shall be either a number or two numbers separated by a hyphen (meaning an inclusive range). The specification ofdays can be made by two fields (day of the month and day of the week). If month, day of month, and day of week are all asterisks,every day shall be matched. If either the month or day of month is specified as an element or list, but the day of week is anasterisk, the month and day of month fields shall specify the days that match. If both month and day of month are specified as anasterisk, but day of week is an element or list, then only the specified days of the week match. Finally, if either the month orday of month is specified as an element or list, and the day of week is also specified as an element or list, then any day matchingeither the month and day of month, or the day of week, shall be matched.</p><p>The sixth field of a line in a crontab entry is a string that shall be executed by <a href="../utilities/sh.html"><i>sh</i></a>at the specified times. A percent sign character in this field shall be translated to a <newline>. Any character preceded bya backslash (including the <tt>'%'</tt> ) shall cause that character to be treated literally. Only the first line (up to a<tt>'%'</tt> or end-of-line) of the command field shall be executed by the command interpreter. The other lines shall be madeavailable to the command as standard input.</p><p>Blank lines and those whose first non- <blank> is <tt>'#'</tt> shall be ignored.</p><p><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">The text files <b>/usr/lib/cron/cron.allow</b> and <b>/usr/lib/cron/cron.deny</b> shall contain zero or more user names, one perline, of users who are, respectively, authorized or denied access to the service underlying the <i>crontab</i> utility. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p></blockquote><h4><a name="tag_04_28_08"></a>ENVIRONMENT VARIABLES</h4><blockquote><p>The following environment variables shall affect the execution of <i>crontab</i>:</p><dl compact><dt><i>EDITOR</i></dt><dd>Determine the editor to be invoked when the <b>-e</b> option is specified. The default editor shall be <a href="../utilities/vi.html"><i>vi</i></a>.</dd><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 and input files).</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_28_09"></a>ASYNCHRONOUS EVENTS</h4><blockquote><p>Default.</p></blockquote><h4><a name="tag_04_28_10"></a>STDOUT</h4><blockquote><p>If the <b>-l</b> option is specified, the crontab entry shall be written to the standard output.</p></blockquote><h4><a name="tag_04_28_11"></a>STDERR</h4><blockquote><p>The standard error shall be used only for diagnostic messages.</p></blockquote><h4><a name="tag_04_28_12"></a>OUTPUT FILES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_28_13"></a>EXTENDED DESCRIPTION</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_28_14"></a>EXIT STATUS</h4><blockquote><p>The following exit values shall be returned:</p><dl compact><dt> 0</dt><dd>Successful completion.</dd><dt>>0</dt><dd>An error occurred.</dd></dl></blockquote><h4><a name="tag_04_28_15"></a>CONSEQUENCES OF ERRORS</h4><blockquote><p>The user's crontab entry is not submitted, removed, edited, or listed.</p></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_04_28_16"></a>APPLICATION USAGE</h4><blockquote><p>The format of the crontab entry shown here is guaranteed only for the POSIX locale. Other cultures may be supported withsubstantially different interfaces, although implementations are encouraged to provide comparable levels of functionality.</p><p>The default settings of the <i>HOME ,</i> <i>LOGNAME ,</i> <i>PATH ,</i> and <i>SHELL</i> variables that are given to thescheduled job are not affected by the settings of those variables when <i>crontab</i> is run; as stated, they are defaults. Thetext about "invoked as specified by this volume of IEEE Std 1003.1-2001" means that the implementation may provideextensions that allow these variables to be affected at runtime, but that the user has to take explicit action in order to accessthe extension, such as give a new option flag or modify the format of the crontab entry.</p><p>A typical user error is to type only <i>crontab</i>; this causes the system to wait for the new crontab entry on standard input.If end-of-file is typed (generally <control>-D), the crontab entry is replaced by an empty file. In this case, the usershould type the interrupt character, which prevents the crontab entry from being replaced.</p></blockquote><h4><a name="tag_04_28_17"></a>EXAMPLES</h4><blockquote><ol><li><p>Clean up <b>core</b> files every weekday morning at 3:15 am:</p><pre><tt>15 3 * * 1-5 find $HOME -name core 2>/dev/null | xargs rm -f</tt></pre></li><li><p>Mail a birthday greeting:</p><pre><tt>0 12 14 2 * mailx john%Happy Birthday!%Time for lunch.</tt></pre></li><li><p>As an example of specifying the two types of days:</p><pre><tt>0 0 1,15 * 1</tt></pre><p>would run a command on the first and fifteenth of each month, as well as on every Monday. To specify days by only one field, theother field should be set to <tt>'*'</tt> ; for example:</p><pre><tt>0 0 * * 1</tt></pre><p>would run a command only on Mondays.</p></li></ol></blockquote><h4><a name="tag_04_28_18"></a>RATIONALE</h4><blockquote><p>All references to a <i>cron</i> daemon and to <i>cron</i> <i>files</i> have been omitted. Although historical implementationshave used this arrangement, there is no reason to limit future implementations.</p><p>This description of <i>crontab</i> is designed to support only users with normal privileges. The format of the input is based onthe System V <i>crontab</i>; however, there is no requirement here that the actual system database used by the <i>cron</i> daemon(or a similar mechanism) use this format internally. For example, systems derived from BSD are likely to have an additional fieldappended that indicates the user identity to be used when the job is submitted.</p><p>The <b>-e</b> option was adopted from the SVID as a user convenience, although it does not exist in all historicalimplementations.</p></blockquote><h4><a name="tag_04_28_19"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_04_28_20"></a>SEE ALSO</h4><blockquote><p><a href="at.html"><i>at</i></a></p></blockquote><h4><a name="tag_04_28_21"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 2.</p></blockquote><h4><a name="tag_04_28_22"></a>Issue 6</h4><blockquote><p>This utility is marked as part of the User Portability Utilities option.</p><p>The normative text is reworded 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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