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doc:howto:cron [2016/04/06 20:00] – [Adding and editing cron jobs] Clarified Sunday is 0. Adapted example to show this. Berninidocs:guide-user:base-system:cron [2023/08/08 11:30] – Added my cronjob to keep last N snapshots of config torxgewinde
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-====== Cron and crontab ======+====== Scheduling tasks with cron ====== 
 +{{section>meta:infobox:howto_links#basic_skills&noheader&nofooter&noeditbutton}}
  
-[[wp>Cron]] allows to run jobs (programs, scripts) at specified times.+===== Introduction ===== 
 +  * OpenWrt can run scheduled tasks using [[wp>Cron|cron]] service. 
 +  * This how-to describes the method for setting up cron jobs
 +  * See also [[docs:guide-user:advanced:watchcat|Watchcat]] to reboot based on schedule or connectivity.
  
-OpenWrt comes with cron system by default, provided by busybox.+===== Goals ===== 
 +  * Run programs or scripts at specific time. 
 +  * Automate scheduled task management.
  
-===== Adding and editing cron jobs =====+===== Web interface instructions ===== 
 +Set up cron jobs using web interface. 
 +  - Navigate to **LuCI -> System -> Scheduled Tasks**. 
 +  - Edit the configuration and click the **Save** button. 
 + 
 +===== Command-line instructions ===== 
 +Set up cron jobs using command-line interface.
  
-You can edit the current config with: 
 <code bash>  <code bash> 
 +# Edit configuration
 crontab -e  crontab -e 
-</code> 
  
-:!: There should be a end-of-line character on the last line of the crontab file.  If in doubt, just leave an empty line at the end.+# Show configuration 
 +crontab -l
  
-Example of time specification: +# Apply changes 
-  +/etc/init.d/cron restart 
-^  min\\ 0-59  ^  hour\\ 0-23  ^  day/month\\ 1-31  ^  month\\ 1-12  ^  day/week\\ 0-6  ^ Description +</code>
-|   */5      *        *    |      |     | every 5 minutes  | +
-|   12    |   */3  |      *    |      |     | every 3 hours at 12 minutes +
-|   57    |   11       15    | 1,6,12 |     | At 11:57 Hrs  on 15th of Jan, June & Dec.  | +
-|   25    |    6        *    |    *    1-5  | At 6:25 AM every weekday (Mon-Fri) +
-|          0    4,12,26  |    *       | At midnight on 4th, 12th and 26th of every month  | +
-|  5,10    9,14  |    10        *    0,4  | At 9:05AM, 9:10AM, 2:05PM and 2:10PM every Sunday and Thursday  |+
  
-<WRAP left round tip 70%> +This will edit the configuraion ''/etc/crontabs/root'' file in [[docs:guide-user:base-system:user.beginner.cli#editing_files|vi editor]].
-0 (zero) is treated as Sunday. If you set the day of the week to 7, busybox will go bonkers and run your command every day. +
-</WRAP> +
-===== Activating cron =====+
  
-Cron is not enabled by default, so your jobs won'be run To activate cron:+:!: There should be a EOL character on the last line of the crontab file. 
 +Just leave an empty line at the end to be sure.
  
-<code bash+===== Task specification ===== 
-/etc/init.d/cron start +Each line is a separate task written in the specification: 
-/etc/init.d/cron enable+ 
 +<code> 
 +* * * * * command to execute 
 +- - - - - 
 +| | | | | 
 +| | | | ----- Day of week (0 - 6) (Sunday =0) 
 +| | | ------- Month (1 - 12) 
 +| | --------- Day (1 - 31) 
 +| ----------- Hour (0 - 23) 
 +------------- Minute (0 - 59)
 </code> </code>
  
-:!: If there is no crontab defined (i.e. ''/etc/crontabs/'' is empty), then cron won't start!  Make sure you already defined cron jobs before trying to start cron.+Examples of time specification:
  
-===== References =====+^  min\\ 0-59  ^  hour\\ 0-23  ^  day/month\\ 1-31  ^  month\\ 1-12  ^  day/week\\ 0-6  ^ Description ^ 
 +|  */5  |  *  |  *  |  *  |  *  | Every 5 minutes | 
 +|  12  |  */3  |  *  |  *  |  *  | Every 3 hours at 12 minutes | 
 +|  57  |  11  |  15  | 1,6,12 |  *  | At 11:57 Hrs on 15th of Jan, June & Dec | 
 +|  25  |  6  |  *  |  *  |  1-5  | At 6:25 AM every weekday (Mon-Fri) | 
 +|  0  |  0  |  4,12,26  |  *  |  *  | At midnight on 4th, 12th and 26th of every month | 
 +|  5,10  |  9,14  |  10  |  *  |  0,4  | At 9:05AM, 9:10AM, 2:05PM and 2:10PM every Sunday and Thursday |
  
-  * [[http://linux.die.net/man/5/crontab|crontab manpage]] +:!0 (zero) is treated as Sunday
-  * [[http://adminschoice.com/crontab-quick-reference]] +If you set the day of the week to 7, BusyBox will go bonkers and run your command every day.
-  * see [[http://www.busybox.net/downloads/BusyBox.html]] for options of the Busybox implementation+
  
-===== Tips and tricks =====+**Table of shortcuts:**
  
-==== Check that the jobs are run ====+^ Shortcut ^ Equivalent ^ Description ^ 
 +| ''@yearly'' | ''0 0 1 1 *'' | Every year | 
 +| ''@annually'' | ''0 0 1 1 *'' | Every year | 
 +| ''@monthly'' | ''0 0 1 * *'' | Every month | 
 +| ''@weekly'' | ''0 0 * * 0'' | Every week | 
 +| ''@daily'' | ''0 0 * * *'' | Every day | 
 +| ''@midnight'' | ''0 0 * * *'' | Every day | 
 +| ''@hourly'' | ''0 * * * *'' | Every hour |
  
-Each time a job is run by cron, a line is printed in OpenWrt logs.  Run ''logread'' to check whether your jobs are correctly run.+:!:  Time shortcuts are not enabled by default. Shortcuts require compiling busybox with FEATURE_CROND_SPECIAL_TIMES enabled in the busybox compile options.
  
-==== Periodic reboot of a router ====+===== Troubleshooting ===== 
 +You can read log messages with:
  
-A simple solution for some hard-to-solve problems (memory leak, performance degradation, ...) is to reboot the router periodically, for instance every night.+<code bash> 
 +logread -e cron 
 +</code>
  
-Howeverthis is not as simple as it seems, becomes router usually have no real-time clock.  This could lead to a never-ending loop of reboot.+Not all messages are loggedto increase logging change ''[[docs:guide-user:base-system:system_configuration|cronloglevel]]'' option.
  
-In the boot process the clock is initially set by ''sysfixtime'' to the most recent timestamp of any file found in /etcThe most recent file is possibly a status file or config file, modified maybe 30 seconds before the reboot initiated by cronSo, in the boot process the clock gets set backwards a few seconds to that file's timestampThen cron starts and notices a few seconds later that the required boot moment has again arrived and reboots again... (At the end of the boot process ntpd starts, and it may also take a while before ntpd gets and sets the correct time, so cron may start the reboot in between.)+===== Extras ===== 
 +==== References ==== 
 +  * [[man>crontab(1)]], [[man>crontab(5)]] 
 +  * [[https://busybox.net/downloads/BusyBox.html#crontab|BusyBox crontab]] 
 +  * [[http://adminschoice.com/crontab-quick-reference|Crontab quick reference]]
  
-One solution for cron is to use a delay and touch a file in /etc before reboot:+==== Periodic reboot ==== 
 +A simple workaround for some hard-to-solve problems (memory leak, performance degradation, ...) is to reboot the router periodically, for instance every night.
  
-<code>+However, this is not as simple as it seems, because the router usually does not have a real-time clock. 
 +This could lead to a never-ending loop of reboots. 
 + 
 +In the boot process the clock is initially set by ''sysfixtime'' to the most recent timestamp of any file found in /etc. 
 +The most recent file is possibly a status file or config file, modified maybe 30 seconds before the reboot initiated by cron. 
 +So, in the boot process the clock gets set backwards a few seconds to that file's timestamp. 
 +Then cron starts and notices a few seconds later that the required boot moment has again arrived and reboots again... 
 +At the end of the boot process ntpd starts, and it may also take a while before ntpd gets and sets the correct time, so cron may start the reboot in between. 
 + 
 +One solution for cron is to use a delay and touch a file in ''/etc'' before reboot. 
 + 
 +<code bash>
 # Reboot at 4:30am every day # Reboot at 4:30am every day
 # Note: To avoid infinite reboot loop, wait 70 seconds # Note: To avoid infinite reboot loop, wait 70 seconds
Line 68: Line 112:
 </code> </code>
  
-:!: On many platforms ''shutdown'' does not work; it will just halt the CPU but it won't power off the device. There is usually no programmable circuitry to actually power off the unit. ''reboot'' does work, in case you should want to reboot the router periodically.+:!: On many platforms ''shutdown'' does not work; it will just halt the CPU but it won't power off the device. 
 +There is usually no programmable circuitry to actually power off the unit. 
 +''reboot'' does work, in case you should want to reboot the router periodically.
  
-==== Alarm clock ====+==== Periodic network restart ==== 
 +A simple solution for restart all your network (lan, wan and wifi) every 10 minutes is this:
  
-If you have [[wp>Daylight saving time]] you could write yourself a nice alarm clock ;-)+<code bash> 
 +*/10 * * * * /etc/init.d/network restart 
 +</code> 
 + 
 +==== Alarm clock ==== 
 +If you have [[wp>Daylight saving time|DST]] you could write yourself a nice alarm clock.
 When DST starts in central Europe, clocks advance from 02:00 CET to 03:00 CEST on last Sunday in March. When DST starts in central Europe, clocks advance from 02:00 CET to 03:00 CEST on last Sunday in March.
-Six day before that, you could make your WOL wake you 10 minutes earlier. Later won't work, you'll be late ;-)+Six day before that, you could make your WoL wake you 10 minutes earlier. 
 +Later won't work, you'll be late.
 When DST ends in central Europe, clocks retreat from 03:00 CEST to 02:00 CET on last Sunday in October. When DST ends in central Europe, clocks retreat from 03:00 CEST to 02:00 CET on last Sunday in October.
  
 <code bash> <code bash>
-#min hour day month dayofweek command +# min hour day month dayofweek command 
-59 05 * * 1 /usr/bin/wol -h 192.168.1.255 xx:xx:xx:xx:xx:xx # Mo +59 05 * * 1 /usr/bin/wol -h 192.168.1.255 xx:xx:xx:xx:xx:xx 
-#crontab must (as fstab) end with the last line as space or a comment+# crontab must end with the last line as space or a comment 
 +</code> 
 + 
 +==== Keep number of configs / snapshots of config ==== 
 +To keep a number N of configurations/settings at the directory "/root", you can also use cron. This way you can access and restore configurations of the past 100 days. The cronjob can easily be extended to copy the config to another device, to be able to replicate a broken OpenWRT device from scratch. 
 + 
 +<code bash> 
 +#Make a new backup/configurations snapshot at nighttime 00:01 am, keep last N=100 snapshots 
 +#01 00 * * * sysupgrade -b "/root/backup-${HOSTNAME}.tar.gz" # <-- keep just one config 
 +01 00 * * * find "/root" -type f -name "backup-*.tar.gz" | sort -r | awk 'NR > 100' | xargs rm -f; sysupgrade -b "/root/backup-${HOSTNAME}-$(date +\%Y-\%m-\%d-\%H-\%M-\%S).tar.gz"
 </code> </code>
  
  • Last modified: 2023/10/14 06:55
  • by vgaetera