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====== AIX crontab / scheduling ======

===== Crontab in edition mode ===== 

You can use either **crontab -e <user>** or a file to overwrite the crontab

Add crontab
<cli prompt='#'>
[root@aixna001]/root# echo '* * * * * /usr/bin/perl /opt/lpar2rrd-agent/lpar2rrd-agent.pl lnxmonitor01 > /var/tmp/lpar2rrd-agent1.out 2>&1' > /tmp/cron_lpar2rrd
[root@aixna001]/root# su - lpar2rrd -c 'crontab  /tmp/cron_lpar2rrd'
</cli>

===== Check crontab ===== 

List crontab for a user
<cli prompt='>'>
[root@aixna001]/root> crontab -l lpar2rrd
0 1 * * * /usr/bin/perl /opt/lpar2rrd-agent/lpar2rrd-agent.pl lnxmonitor01 > /var/tmp/lpar2rrd-agent.out 2>&1
40 18 * * 1,2,3,4,5 ( . /home/lpar/.bash_profile ; /myscript/script01.sh ) >/dev/null 2>&1
</cli>

Check latest appied crontab
<cli prompt='>'>
[root@aixna001]/root> crontab -v lpar2rrd
Crontab file: lpar2rrd     Submission time: Thu Jan 11 09:32:45 CET 2024
</cli>

Fields description
  * minute:          0 through 59
  * hour:            0 through 23
  * day_of_month:    1 through 31
  * month:           1 through 12
  * weekday:         0 through 6 for Sunday through Saturday

FIXME
On linux (NOT AIX) you can also use for very 10 minutes, */10  
   0,10,20,30,40,50 6 * * 1-5 /usr/bin/calendar
   */10 * * 1-5 /usr/bin/calendar

==== Cron log ====

Default log output is located in**/var/adm/cron/log**

You can use logrotate mechanism to rotate this log, or choose the following steps

=== Crontab and log management ===

By default on AIX cron process use the file **/etc/cronlog.conf** to customize cronlog.\\
In this file you can easily rotate cron logfile.

To log information in directory /var/cronjobs, log file cron.out, size of 50k, total number of rotated files = 4, archive in /var/cronarch, archive files with compression, create the configuration file as follows:

<cli prompt='>'>
[root@aix001] /root> cat  /etc/cronlog.conf
...
logfile=/var/cronjobs/cron.out 
  size=50K 
  rotate=4 
  archive=/var/cronarch
  compress
</cli>

==== Errors ====

I found that the log is located in **/var/adm/log**. Further we are getting this error repeatedly ever since this date/time. How do I clear this max limit?
  c queue max run limit reached Fri Nov 25 21:52:00 2016
  ! rescheduling a cron job Fri Nov 25 21:52:00 2016
  
The cron daemon has a limit of how many jobs it can run simultaneously. By default it is 100 jobs. If a new job is scheduled to run, and the limit has already been reached, the job will be rescheduled at a later time (the default is 60 seconds later). Both the number of jobs and wait time are configured in the file **/var/adm/cron/queuedefs**.

To do this, add an entry to the bottom of the /var/adm/cron/queuedefs file using an editor such as vi. The entry should have the form:
  c.50j20n60w
where
  * c. = The "c" or cron queue, followed by a period separator.
  * Nj = The maximum number of jobs to be run simultaneously by cron, followed by the letter "j".
  * Nn = The "nice" value of the jobs to be run (default is 2), followed by the letter "n".
  * Nw = The time a job has to wait until the next attempt to run it, followed by the letter "w".

For example:
  This example would set the cron queue to a maximum of 200 jobs, with a nice value of 2, and a wait time of 60 seconds.
<cli prompt='#'>
root@orathal-test /var/tmp# cat /var/adm/cron/queuedefs
c.200j2n60w
</cli>

c.200j2n60w
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