Lab 14.6. Scheduling a Periodic Task with cron
Hi,
From previous knowledge, I so far created any coronjobs with the "crontab -e" command. According to the solution in Lab 14.6. I'm supposed to create a crontab file named "mycrontab". But where do I have to create this file? In /etc/crontab.d/?
Thnaks.
Answers
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Hi @albiurs,
But where do I have to create this file? In /etc/crontab.d/?
Crontab can read a file and create a crontab based on the instructions of it. So, in this case we are using a file called "mycrontab" to store and pass instructions to crontab. For that reason it can be anywhere, because it will be read just once, then a new crontab file will be created in the appropriate place.
Regards,
Luis.0 -
Hi Luis,
Thanks a lot for your replay and sorry for the late response.
I still do not fully understand. For example if I create a new file like ~/Documents/mycrontab with vim, and add some cronjob direction to it, it will not do anything yet. Somehow I have to tell the OS that this file must be read and interpreted by cron. So this has to be done with the
crontabcommand likecrontab path/to/file, right? But what happens then? Do I still need the original the original mycrontab file and where will the final file be crated? And what about the /etc/cron.* directories? If I do anls -l /etc/cron.{d,hourly,daily,weekly,monthly}I see that there are already a lot of files inside these folders:┌──(alu@qtwixnb)-[~] └─$ ls -l /etc/cron.{d,hourly,daily,weekly,monthly} /etc/cron.d: total 20 -rw-r--r-- 1 root root 285 Jan 10 2023 anacron -rw-r--r-- 1 root root 201 Mar 5 2023 e2scrub_all -rw-r--r-- 1 root root 396 Dec 4 2022 sysstat -rw-r--r-- 1 root root 158 Mar 23 21:08 timeshift-boot -rw-r--r-- 1 root root 137 Mar 23 21:08 timeshift-hourly /etc/cron.daily: total 56 -rwxr-xr-x 1 root root 311 Jan 10 2023 0anacron -rwxr-xr-x 1 root root 1478 May 25 2023 apt-compat -rwxr-xr-x 1 root root 314 Aug 17 2021 aptitude -rwxr-xr-x 1 root root 123 Mar 27 2023 dpkg -rwxr-xr-x 1 root root 4722 Sep 29 2023 exim4-base lrwxrwxrwx 1 root root 37 Sep 10 03:08 google-chrome -> /opt/google/chrome/cron/google-chrome -rwxr-xr-x 1 root root 2211 Feb 10 2018 locate -rwxr-xr-x 1 root root 377 Dec 14 2022 logrotate -rwxr-xr-x 1 root root 1395 Mar 12 2023 man-db lrwxrwxrwx 1 root root 41 Sep 5 02:26 microsoft-edge -> /opt/microsoft/msedge/cron/microsoft-edge -rwxr-xr-x 1 root root 7175 Sep 12 06:33 opera-browser -rwxr-xr-x 1 root root 518 Dec 4 2022 sysstat /etc/cron.hourly: total 0 /etc/cron.monthly: total 4 -rwxr-xr-x 1 root root 313 Jan 10 2023 0anacron /etc/cron.weekly: total 8 -rwxr-xr-x 1 root root 312 Jan 10 2023 0anacron -rwxr-xr-x 1 root root 1055 Mar 12 2023 man-dbThanks.
Regards,
Urs0 -
Hi Urs,
I still do not fully understand. For example if I create a new file like ~/Documents/mycrontab with vim, >and add some cronjob direction to it, it will not do anything yet.
That's right.
Somehow I have to tell the OS that this file must be read and interpreted by cron. So this has to be >done with the crontab command like crontab path/to/file , right?
Exactly.
But what happens then? Do I still need the original the original mycrontab file and where will the final >file be crated? And what about the /etc/cron.* directories?
You don't need the original file anymore, because the content of the file has been stored already. It's in the following directory:
/var/spool/cron/crontabs
So, the crontab file will be the user's name that you are working with. And if you look into the file, you will see the crontab's data:
cat /var/spool/cron/crontabs/ubuntu
DO NOT EDIT THIS FILE - edit the master and reinstall.
(mycrontab installed on Mon Sep 16 10:09:06 2024)
(Cron version -- $Id: crontab.c,v 2.13 1994/01/17 03:20:37 vixie Exp $)
0 10 * * * /tmp/myjob.sh
In my case the user's name is ubuntu.
I hope that helps!
Many regards,
Luis.0 -
Hi Luis,
Thank you very much. I got it now. I was just confused because I always edited the crontab directly and never used an input file to create / overwrite the crontab.
Best wishes,
Urs1 -
It's a pleasure, Urs!
Regards,
Luis.0
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