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howtos:general_admin:task_scheduling [2015/06/24 14:39 (UTC)] tdrssb Added section on Interactive at (cmd) |
howtos:general_admin:task_scheduling [2015/06/24 19:36 (UTC)] (current) tdrssb |
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| Line 17: | Line 17: | ||
| </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. | ||
| Line 27: | Line 27: | ||
| 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===== | ||
| Line 52: | Line 84: | ||
| 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: | ||
| Line 71: | Line 112: | ||
| </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 ====== | ||
| Line 85: | Line 120: | ||
| * 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}} | ||
