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howtos:general_admin:task_scheduling [2015/06/24 14:39 (UTC)] – Added section on Interactive at (cmd) tdrssbhowtos:general_admin:task_scheduling [2015/06/24 19:36 (UTC)] (current) – tdrssb
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 </code> </code>
  
-======Interactive at======+=====Interactive at=====
 Using the command **//at//** with standard input (keyboard) is a little more complicated than typing one line in at the prompt. The command uses an internal "sub-shell" to gather the required information. Once the command information entry is complete, <key>Ctrl-D</key> (EOT) will signify entry completion. The **//-m//** flag specifies a mail message will be sent to the user when the job is finished, regardless if any output was created. Using the command **//at//** with standard input (keyboard) is a little more complicated than typing one line in at the prompt. The command uses an internal "sub-shell" to gather the required information. Once the command information entry is complete, <key>Ctrl-D</key> (EOT) will signify entry completion. The **//-m//** flag specifies a mail message will be sent to the user when the job is finished, regardless if any output was created.
  
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 job 4 at 2015-06-22 12:01  job 4 at 2015-06-22 12:01 
 darkstar:~%  darkstar:~% 
 +</code>
 +
 +=====File-driven at=====
 +Commands can also be contained within a file and run by **//at//**:
 +<code>
 +darkstar:~% at 12:32 -m -f /usr/local/bin/my_script.sh
 +warning: commands will be executed using (in order) a) $SHELL b) login shell c) /bin/sh
 +job 8 at 2015-06-22 12:10
 +</code>
 +The **-m** flag will email the user after completion of the command; the **-f** flag specifies the command will read the job from a file, not from standard input. After the command is typed in (and the appropriate warning is displayed), the **//at//** job number((As distinct from a process ID (PID) known to the operating system)) is displayed.
 +
 +=====at Internal Scheduling=====
 +The job numbers provided after a command is typed in, or when a file is read, allow the user to know which internal job will be run in sequential order. If a user wants to delete a specific task, all that needs to be known is this internal job number. To remove the job, the command **//atrm//** (**__at__ __r__e__m__ove**) is used:
 +
 +<code>
 +darkstar:~%  at -l
 +7      2015-06-22 12:10 p tux
 +8      2015-06-22 12:15 p root
 +</code>
 +
 +The command **//atq//** (**__at__ __q__ueue**) is the same as **//at -l//**:
 +
 +<code>
 +darkstar:~%  atq
 +7      2015-06-22 12:10 p tux
 +8      2015-06-22 12:15 p root
 +</code>
 +
 +To remove the user job, use **//atrm//** with the job number:
 +<code>
 +darkstar:~%  atrm 7
 +</code>
  
 =====Using cron===== =====Using cron=====
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 The //crontab// file syntax is: The //crontab// file syntax is:
  
-minute(0-59) hour(0-23) day(1-31) month(1-12) weekday(0-6) command+<code> 
 + # * * * * *  command to execute 
 + # │ │ │ │ │ 
 + # │ │ │ │ │ 
 + # │ │ │ │ └───── day of week (0 - 6) (Sun(0) /Mon (1)/Tue (2)/Wed (3)/Thu (4)/Fri (5)/Sat (6)) 
 + # │ │ │ └────────── month (1 - 12) 
 + # │ │ └─────────────── day of month (1 - 31) 
 + # │ └──────────────────── hour (0 - 23) 
 + # └───────────────────────── min (0 - 59) 
 +</code>
  
 Using an asterisk in any placeholder location, will match any value. For example, the following will run //example_script.sh// at noon (1200) everyday during the first three months of the year: Using an asterisk in any placeholder location, will match any value. For example, the following will run //example_script.sh// at noon (1200) everyday during the first three months of the year:
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 </note> </note>
  
- +**//anacron//** is unique from **//cron//** in the respect that it does not expect the operating system to be running continuously like a 24x7 server. If the time of execution passes while the system is turned off, **//anacron//** executes the command automatically when the machine is turned back on. The reverse is **not** true for **//cron//** - if the computer is turned off during the time of scheduled execution, **//cron//** will not execute the job. Another key difference between **//anacron//** and **//cron//** is the minimum chronological "granularity" - **//anacron//** can only execute jobs by //day//, versus the ability of **//cron//** to execute by the //minute//. Finally, **//anacron//** can __only__ be used by root, while **//cron//** can be used by root and normal users.
- +
-<note> +
-The links in red are to non-existent articles. +
- +
-If you are experienced with those tools, please feel free to write the articles. +
-</note>+
  
 ====== Sources ====== ====== Sources ======
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   * Originally written by [[wiki:user:vharishankar | vharishankar]]   * Originally written by [[wiki:user:vharishankar | vharishankar]]
   * Contrbutions by [[wiki:user:mfillpot |mfillpot]], [[wiki:user:tdrssb |tdrssb]]   * Contrbutions by [[wiki:user:mfillpot |mfillpot]], [[wiki:user:tdrssb |tdrssb]]
 +  * Example crontab example modified from [[en.wikipedia.org/wiki/cron]]
 <!-- Please do not modify anything below, except adding new tags.--> <!-- Please do not modify anything below, except adding new tags.-->
 <!-- You must also remove the tag-word "template" below. Otherwise your page will not show up in the Table of Contents --> <!-- You must also remove the tag-word "template" below. Otherwise your page will not show up in the Table of Contents -->
 {{tag>howtos task_scheduling needs_attention author_vharishankar author_mfillpot}} {{tag>howtos task_scheduling needs_attention author_vharishankar author_mfillpot}}
  

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