1028 lines
13 KiB
HTML
1028 lines
13 KiB
HTML
<HTML
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><HEAD
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>Scheduling Commands to run in the background</TITLE
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>GNU/Linux Command-Line Tools Summary</TH
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><TD
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WIDTH="10%"
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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CLASS="CHAPTER"
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><H1
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><A
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NAME="SCHEDULING"
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></A
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>Chapter 18. Scheduling Commands to run in the background</H1
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><P
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>There are two main tools used to perform <A
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NAME="AEN10869"
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></A
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>scheduled <A
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NAME="AEN10871"
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></A
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>tasks, <SPAN
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CLASS="emphasis"
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><I
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CLASS="EMPHASIS"
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>at</I
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></SPAN
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> and <SPAN
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CLASS="emphasis"
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><I
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CLASS="EMPHASIS"
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>cron</I
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></SPAN
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>. You may also like to try <A
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HREF="http://anacron.sourceforge.net"
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TARGET="_top"
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>anacron</A
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><A
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NAME="AEN10876"
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></A
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> if your computer <A
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NAME="AEN10878"
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></A
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>does not run continuously, as cron <A
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NAME="AEN10880"
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></A
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>will only work if your computer is left on (anacron can catch <A
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NAME="AEN10882"
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></A
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>up with the scheduled <A
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NAME="AEN10884"
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></A
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>tasks the next time the computer is on...).</P
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><P
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></P
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><DIV
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CLASS="VARIABLELIST"
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><DL
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><DT
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>at</DT
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><DD
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><P
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><A
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NAME="AEN10891"
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></A
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>'at' executes a command once on a particular <A
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NAME="AEN10893"
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></A
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>day,<A
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NAME="AEN10895"
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></A
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> at <A
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NAME="AEN10897"
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></A
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>a particular time.<A
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NAME="AEN10899"
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></A
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> <SPAN
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CLASS="emphasis"
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><I
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CLASS="EMPHASIS"
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>at</I
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></SPAN
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> will add <A
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NAME="AEN10902"
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></A
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>a particular command to be executed.</P
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><P
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>Examples:</P
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><PRE
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CLASS="SCREEN"
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>at 21:30</PRE
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><P
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>You then type the commands you want executed then press <A
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NAME="AEN10907"
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></A
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>the end-of-file<A
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NAME="AEN10909"
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></A
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> key <A
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NAME="AEN10911"
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></A
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>(normally
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<B
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CLASS="KEYCAP"
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>CTRL</B
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>-<B
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CLASS="KEYCAP"
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>D</B
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>
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<A
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NAME="AEN10916"
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></A
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>
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). Also try:</P
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><PRE
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CLASS="SCREEN"
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>at now + time</PRE
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><P
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>This will run at the current time + the hours/mins/seconds you specify<A
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NAME="AEN10920"
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></A
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> (use<SPAN
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CLASS="emphasis"
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><I
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CLASS="EMPHASIS"
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> at <A
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NAME="AEN10923"
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></A
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>now + 1 hour <A
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NAME="AEN10925"
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></A
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></I
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></SPAN
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>to have command(s) run in 1 hour from now...)</P
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><P
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>You can also use the <SPAN
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CLASS="emphasis"
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><I
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CLASS="EMPHASIS"
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>-f<A
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NAME="AEN10929"
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></A
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></I
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></SPAN
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> option to have at <A
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NAME="AEN10931"
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></A
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>execute a particular <A
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NAME="AEN10933"
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></A
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>file (a shell <A
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NAME="AEN10935"
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></A
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>script).</P
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><PRE
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CLASS="SCREEN"
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>at -f shell_script now + 1 hour</PRE
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><P
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>This would run the shell <A
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NAME="AEN10939"
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></A
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>script 1 hour <A
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NAME="AEN10941"
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></A
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>from now.</P
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></DD
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><DT
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>atq</DT
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><DD
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><P
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><A
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NAME="AEN10947"
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></A
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>Will list jobs currently in queue <A
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NAME="AEN10949"
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></A
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>for the user who executed it, if root<A
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NAME="AEN10951"
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></A
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> executes at <A
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NAME="AEN10953"
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></A
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>it will list <A
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NAME="AEN10955"
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></A
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>all jobs <A
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NAME="AEN10957"
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></A
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>in queue <A
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NAME="AEN10959"
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></A
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>for the at <A
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NAME="AEN10961"
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></A
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>daemon. Doesn't need or take any options.<A
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NAME="AEN10963"
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></A
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></P
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></DD
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><DT
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>atrm</DT
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><DD
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><P
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><A
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NAME="AEN10969"
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></A
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>Will remove <A
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NAME="AEN10971"
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></A
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>a job <A
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NAME="AEN10973"
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></A
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>from the 'at' queue.<A
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NAME="AEN10975"
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></A
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></P
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><P
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>Command syntax:</P
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><PRE
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CLASS="SCREEN"
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>atrm job_no</PRE
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><P
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>Will delete <A
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NAME="AEN10980"
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></A
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>the job <A
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NAME="AEN10982"
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></A
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>“job_no” (use <SPAN
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CLASS="emphasis"
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><I
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CLASS="EMPHASIS"
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>atq</I
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></SPAN
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> to find out the number <A
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NAME="AEN10985"
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></A
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>of the job)</P
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></DD
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><DT
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>cron<SPAN
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CLASS="emphasis"
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><I
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CLASS="EMPHASIS"
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></I
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></SPAN
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></DT
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><DD
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><P
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>cron<A
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NAME="AEN10992"
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></A
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> can be used to schedule <A
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NAME="AEN10994"
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></A
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>a particular <A
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NAME="AEN10996"
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></A
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>function <A
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NAME="AEN10998"
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></A
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>to occur every minute,<A
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NAME="AEN11000"
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></A
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> hour,<A
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NAME="AEN11002"
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></A
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> day,<A
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NAME="AEN11004"
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></A
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> week, or month.<A
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NAME="AEN11006"
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></A
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> </P
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><P
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>It's normal <A
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NAME="AEN11009"
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></A
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>to use the crontab <A
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NAME="AEN11011"
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></A
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>to perform the editing <A
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NAME="AEN11013"
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></A
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>functions as this automates <A
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NAME="AEN11015"
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></A
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>the process <A
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NAME="AEN11017"
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></A
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>for the cron <A
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NAME="AEN11019"
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></A
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>daemon <A
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NAME="AEN11021"
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></A
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>and makes it easier for normal<A
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NAME="AEN11023"
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></A
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> users to use cron.<A
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NAME="AEN11025"
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></A
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></P
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><DIV
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CLASS="TIP"
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><BLOCKQUOTE
|
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CLASS="TIP"
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><P
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><B
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>Anacron: </B
|
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><SPAN
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CLASS="emphasis"
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><I
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CLASS="EMPHASIS"
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>anacron</I
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></SPAN
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> is another tool designed for systems which are not always on, such as home computers</P
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><P
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>While <SPAN
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CLASS="emphasis"
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><I
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CLASS="EMPHASIS"
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>cron </I
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></SPAN
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>will not run if the computer is off, <SPAN
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CLASS="emphasis"
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><I
|
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CLASS="EMPHASIS"
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>anacron </I
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></SPAN
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>will simply run the command when the computer is next on (it catches up with things).</P
|
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></BLOCKQUOTE
|
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></DIV
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><P
|
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></P
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></DD
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><DT
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>crontab</DT
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><DD
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><P
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><A
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NAME="AEN11039"
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></A
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><SPAN
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CLASS="emphasis"
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><I
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CLASS="EMPHASIS"
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>crontab</I
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></SPAN
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> is used to edit,<A
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NAME="AEN11042"
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></A
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> read and remove <A
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NAME="AEN11044"
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></A
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>the files which the cron <A
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NAME="AEN11046"
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></A
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>daemon <A
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NAME="AEN11048"
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></A
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>reads.<A
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NAME="AEN11050"
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></A
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> </P
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><P
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>Options <A
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NAME="AEN11053"
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></A
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>for crontab <A
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NAME="AEN11055"
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></A
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>(use<SPAN
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CLASS="emphasis"
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><I
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CLASS="EMPHASIS"
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> crontab <A
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NAME="AEN11058"
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></A
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>-option(s)</I
|
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></SPAN
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>):</P
|
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><P
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></P
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><UL
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><LI
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><P
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><SPAN
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CLASS="emphasis"
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><I
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CLASS="EMPHASIS"
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>-e<A
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NAME="AEN11064"
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></A
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></I
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></SPAN
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> --- to edit the file.</P
|
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></LI
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><LI
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><P
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><SPAN
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CLASS="emphasis"
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><I
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CLASS="EMPHASIS"
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>-l<A
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NAME="AEN11069"
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></A
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> </I
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></SPAN
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>--- to list the contents <A
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NAME="AEN11071"
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></A
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>of the file.</P
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></LI
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><LI
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><P
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><SPAN
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CLASS="emphasis"
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><I
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CLASS="EMPHASIS"
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>-u <A
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NAME="AEN11076"
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></A
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>username </I
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></SPAN
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>--- use the <SPAN
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CLASS="emphasis"
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><I
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CLASS="EMPHASIS"
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>-u</I
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></SPAN
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> with a username <A
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NAME="AEN11079"
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></A
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>argument <A
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NAME="AEN11081"
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></A
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>to work with another users crontab <A
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NAME="AEN11083"
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></A
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>file.</P
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></LI
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></UL
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><P
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>When using <SPAN
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CLASS="emphasis"
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><I
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CLASS="EMPHASIS"
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> crontab -e <A
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NAME="AEN11087"
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></A
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></I
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></SPAN
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>you have a number of fields <A
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NAME="AEN11089"
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></A
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>(6) what they mean is listed <A
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NAME="AEN11091"
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></A
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>below:</P
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><P
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><DIV
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CLASS="INFORMALTABLE"
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><A
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NAME="AEN11094"
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></A
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><P
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></P
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><TABLE
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BORDER="1"
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CLASS="CALSTABLE"
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><TBODY
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><TR
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><TD
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WIDTH="50%"
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ALIGN="CENTER"
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VALIGN="TOP"
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><P
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>Field</P
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></TD
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><TD
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WIDTH="50%"
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ALIGN="CENTER"
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VALIGN="TOP"
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><P
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>Allowed Values</P
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></TD
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></TR
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><TR
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><TD
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WIDTH="50%"
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ALIGN="CENTER"
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VALIGN="TOP"
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><P
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>minute</P
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></TD
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><TD
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WIDTH="50%"
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ALIGN="CENTER"
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VALIGN="TOP"
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><P
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>0-59</P
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></TD
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></TR
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><TR
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><TD
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WIDTH="50%"
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ALIGN="CENTER"
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VALIGN="TOP"
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><P
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>hour</P
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></TD
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><TD
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WIDTH="50%"
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ALIGN="CENTER"
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VALIGN="TOP"
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><P
|
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>0-23</P
|
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></TD
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></TR
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><TR
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><TD
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WIDTH="50%"
|
|
ALIGN="CENTER"
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VALIGN="TOP"
|
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><P
|
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>day of month</P
|
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></TD
|
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><TD
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WIDTH="50%"
|
|
ALIGN="CENTER"
|
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VALIGN="TOP"
|
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><P
|
|
>1-31</P
|
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></TD
|
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></TR
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><TR
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><TD
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WIDTH="50%"
|
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ALIGN="CENTER"
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VALIGN="TOP"
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><P
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>month</P
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></TD
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><TD
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WIDTH="50%"
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ALIGN="CENTER"
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VALIGN="TOP"
|
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><P
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>1-12 (or names, see below)</P
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></TD
|
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></TR
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><TR
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><TD
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WIDTH="50%"
|
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ALIGN="CENTER"
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VALIGN="TOP"
|
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><P
|
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>day of week</P
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></TD
|
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><TD
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WIDTH="50%"
|
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ALIGN="CENTER"
|
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VALIGN="TOP"
|
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><P
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>0-7 (0 or 7 is Sun, or use three letter names)</P
|
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></TD
|
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></TR
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></TBODY
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></TABLE
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><P
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></P
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></DIV
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></P
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><P
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>There are also a number of shortcut <A
|
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NAME="AEN11130"
|
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></A
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>methods for common <A
|
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NAME="AEN11132"
|
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></A
|
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>tasks, including:<A
|
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NAME="AEN11134"
|
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></A
|
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><A
|
|
NAME="AEN11136"
|
|
HREF="#FTN.AEN11136"
|
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><SPAN
|
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CLASS="footnote"
|
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>[1]</SPAN
|
|
></A
|
|
></P
|
|
><P
|
|
></P
|
|
><UL
|
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><LI
|
|
><P
|
|
><SPAN
|
|
CLASS="emphasis"
|
|
><I
|
|
CLASS="EMPHASIS"
|
|
>@reboot</I
|
|
></SPAN
|
|
> --- run <A
|
|
NAME="AEN11143"
|
|
></A
|
|
>command at <A
|
|
NAME="AEN11145"
|
|
></A
|
|
>reboot </P
|
|
></LI
|
|
><LI
|
|
><P
|
|
><SPAN
|
|
CLASS="emphasis"
|
|
><I
|
|
CLASS="EMPHASIS"
|
|
>@yearly</I
|
|
></SPAN
|
|
> --- same as 0 0 1 1 * </P
|
|
></LI
|
|
><LI
|
|
><P
|
|
><SPAN
|
|
CLASS="emphasis"
|
|
><I
|
|
CLASS="EMPHASIS"
|
|
>@annually</I
|
|
></SPAN
|
|
> --- same as @yearly </P
|
|
></LI
|
|
><LI
|
|
><P
|
|
><SPAN
|
|
CLASS="emphasis"
|
|
><I
|
|
CLASS="EMPHASIS"
|
|
>@monthly</I
|
|
></SPAN
|
|
> --- same as 0 0 1 * * </P
|
|
></LI
|
|
><LI
|
|
><P
|
|
><SPAN
|
|
CLASS="emphasis"
|
|
><I
|
|
CLASS="EMPHASIS"
|
|
>@weekly</I
|
|
></SPAN
|
|
> --- same as 0 0 * * 0 </P
|
|
></LI
|
|
><LI
|
|
><P
|
|
><SPAN
|
|
CLASS="emphasis"
|
|
><I
|
|
CLASS="EMPHASIS"
|
|
>@daily</I
|
|
></SPAN
|
|
> --- same as 0 0 * * * </P
|
|
></LI
|
|
><LI
|
|
><P
|
|
><SPAN
|
|
CLASS="emphasis"
|
|
><I
|
|
CLASS="EMPHASIS"
|
|
>@midnight</I
|
|
></SPAN
|
|
> --- same as @daily </P
|
|
></LI
|
|
><LI
|
|
><P
|
|
><SPAN
|
|
CLASS="emphasis"
|
|
><I
|
|
CLASS="EMPHASIS"
|
|
>@hourly</I
|
|
></SPAN
|
|
> --- same as 0 * * * * </P
|
|
></LI
|
|
></UL
|
|
><P
|
|
><A
|
|
NAME="AEN11169"
|
|
HREF="#FTN.AEN11169"
|
|
><SPAN
|
|
CLASS="footnote"
|
|
>[2]</SPAN
|
|
></A
|
|
></P
|
|
><P
|
|
>Note that * (asterisk) is used to mean anything (similar to the wildcard). For example if you leave the day <A
|
|
NAME="AEN11173"
|
|
></A
|
|
>part (the 5th place) with an asterisk<A
|
|
NAME="AEN11175"
|
|
></A
|
|
> it would mean everyday.<A
|
|
NAME="AEN11177"
|
|
></A
|
|
></P
|
|
><P
|
|
>Lists <A
|
|
NAME="AEN11180"
|
|
></A
|
|
>are allowed.<A
|
|
NAME="AEN11182"
|
|
></A
|
|
> A list is a set <A
|
|
NAME="AEN11184"
|
|
></A
|
|
>of numbers <A
|
|
NAME="AEN11186"
|
|
></A
|
|
>(or ranges) separated <A
|
|
NAME="AEN11188"
|
|
></A
|
|
>by commas.<A
|
|
NAME="AEN11190"
|
|
></A
|
|
> Examples:<A
|
|
NAME="AEN11192"
|
|
></A
|
|
> ``1,2,5,9'', ``0-4,8-12”.</P
|
|
><P
|
|
>Step <A
|
|
NAME="AEN11195"
|
|
></A
|
|
>values <A
|
|
NAME="AEN11197"
|
|
></A
|
|
>can be used in conjunction <A
|
|
NAME="AEN11199"
|
|
></A
|
|
>with ranges.<A
|
|
NAME="AEN11201"
|
|
></A
|
|
> Following <A
|
|
NAME="AEN11203"
|
|
></A
|
|
>a range <A
|
|
NAME="AEN11205"
|
|
></A
|
|
>with ``/<number>'' specifies <A
|
|
NAME="AEN11207"
|
|
></A
|
|
>skips of the number's value<A
|
|
NAME="AEN11209"
|
|
></A
|
|
> through the range. For example, ``0-23/2'' can be used in the hours <A
|
|
NAME="AEN11211"
|
|
></A
|
|
>field <A
|
|
NAME="AEN11213"
|
|
></A
|
|
>to specify <A
|
|
NAME="AEN11215"
|
|
></A
|
|
>command execution <A
|
|
NAME="AEN11217"
|
|
></A
|
|
>every other hour <A
|
|
NAME="AEN11219"
|
|
></A
|
|
>(the alternative <A
|
|
NAME="AEN11221"
|
|
></A
|
|
>in the V7 <A
|
|
NAME="AEN11223"
|
|
></A
|
|
>standard is ``0,2,4,6,8,10,12,14,16,18,20,22''). Steps <A
|
|
NAME="AEN11225"
|
|
></A
|
|
>are also permitted <A
|
|
NAME="AEN11227"
|
|
></A
|
|
>after an asterisk,<A
|
|
NAME="AEN11229"
|
|
></A
|
|
> so if you want to say ``every two hours'', just use ``*/2''.</P
|
|
><P
|
|
>When writing <A
|
|
NAME="AEN11232"
|
|
></A
|
|
>a crontab <A
|
|
NAME="AEN11234"
|
|
></A
|
|
>entry <A
|
|
NAME="AEN11236"
|
|
></A
|
|
>you simply type in six <A
|
|
NAME="AEN11238"
|
|
></A
|
|
>fields separated <A
|
|
NAME="AEN11240"
|
|
></A
|
|
>by spaces,<A
|
|
NAME="AEN11242"
|
|
></A
|
|
> the first five <A
|
|
NAME="AEN11244"
|
|
></A
|
|
>are those listed in the table <A
|
|
NAME="AEN11246"
|
|
></A
|
|
>(using numbers <A
|
|
NAME="AEN11248"
|
|
></A
|
|
>or letters <A
|
|
NAME="AEN11250"
|
|
></A
|
|
>and numbers <A
|
|
NAME="AEN11252"
|
|
></A
|
|
>as appropriate), the 6th field <A
|
|
NAME="AEN11254"
|
|
></A
|
|
>is the command to be executed and any options, cron <A
|
|
NAME="AEN11256"
|
|
></A
|
|
>will read everything <A
|
|
NAME="AEN11258"
|
|
></A
|
|
>up until the newline.<A
|
|
NAME="AEN11260"
|
|
></A
|
|
></P
|
|
><P
|
|
>Example:</P
|
|
><PRE
|
|
CLASS="SCREEN"
|
|
>5 4 * * sun echo "run at 5 after 4 every sunday"</PRE
|
|
><P
|
|
>This would run the echo <A
|
|
NAME="AEN11265"
|
|
></A
|
|
>command with the string <A
|
|
NAME="AEN11267"
|
|
></A
|
|
>shown at 4:05 every Sunday.</P
|
|
></DD
|
|
></DL
|
|
></DIV
|
|
><P
|
|
></P
|
|
></DIV
|
|
><H3
|
|
CLASS="FOOTNOTES"
|
|
>Notes</H3
|
|
><TABLE
|
|
BORDER="0"
|
|
CLASS="FOOTNOTES"
|
|
WIDTH="100%"
|
|
><TR
|
|
><TD
|
|
ALIGN="LEFT"
|
|
VALIGN="TOP"
|
|
WIDTH="5%"
|
|
><A
|
|
NAME="FTN.AEN11136"
|
|
HREF="c10866.htm#AEN11136"
|
|
><SPAN
|
|
CLASS="footnote"
|
|
>[1]</SPAN
|
|
></A
|
|
></TD
|
|
><TD
|
|
ALIGN="LEFT"
|
|
VALIGN="TOP"
|
|
WIDTH="95%"
|
|
><P
|
|
>This information has come from (without editing) a post on the LinuxChix techtalk mailing list, please see [16] in the <A
|
|
HREF="b12722.htm"
|
|
><I
|
|
>Bibliography</I
|
|
></A
|
|
> for further information.</P
|
|
></TD
|
|
></TR
|
|
><TR
|
|
><TD
|
|
ALIGN="LEFT"
|
|
VALIGN="TOP"
|
|
WIDTH="5%"
|
|
><A
|
|
NAME="FTN.AEN11169"
|
|
HREF="c10866.htm#AEN11169"
|
|
><SPAN
|
|
CLASS="footnote"
|
|
>[2]</SPAN
|
|
></A
|
|
></TD
|
|
><TD
|
|
ALIGN="LEFT"
|
|
VALIGN="TOP"
|
|
WIDTH="95%"
|
|
><P
|
|
>This information comes from the cron manual page with small additions (no changes to original content), refer to [13] in the <A
|
|
HREF="b12722.htm"
|
|
><I
|
|
>Bibliography</I
|
|
></A
|
|
> for further information.</P
|
|
></TD
|
|
></TR
|
|
></TABLE
|
|
><DIV
|
|
CLASS="NAVFOOTER"
|
|
><HR
|
|
ALIGN="LEFT"
|
|
WIDTH="100%"><TABLE
|
|
SUMMARY="Footer navigation table"
|
|
WIDTH="100%"
|
|
BORDER="0"
|
|
CELLPADDING="0"
|
|
CELLSPACING="0"
|
|
><TR
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="left"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="c10694.htm"
|
|
ACCESSKEY="P"
|
|
>Prev</A
|
|
></TD
|
|
><TD
|
|
WIDTH="34%"
|
|
ALIGN="center"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="book1.htm"
|
|
ACCESSKEY="H"
|
|
>Home</A
|
|
></TD
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="right"
|
|
VALIGN="top"
|
|
><A
|
|
HREF="c11270.htm"
|
|
ACCESSKEY="N"
|
|
>Next</A
|
|
></TD
|
|
></TR
|
|
><TR
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="left"
|
|
VALIGN="top"
|
|
>Working with MS-DOS files</TD
|
|
><TD
|
|
WIDTH="34%"
|
|
ALIGN="center"
|
|
VALIGN="top"
|
|
> </TD
|
|
><TD
|
|
WIDTH="33%"
|
|
ALIGN="right"
|
|
VALIGN="top"
|
|
>Miscellaneous</TD
|
|
></TR
|
|
></TABLE
|
|
></DIV
|
|
></BODY
|
|
></HTML
|
|
> |