3
$ sudo cat /etc/crontab
# ...comment lines elided... 
0 0,12 * * * root sleep 1347 && certbot renew -q --post-hook 'sudo reboot'

sudo crontab -e shows

13 0,12 * * * root sleep 1347 && certbot renew -q

This VM is a simple default-configured Google Compute Engine VM with Debian Buster. I am logged in as a user joshua, but note that sudo does not require entering a password.

Which one (or perhaps both?) shows what cron actually does? What is the recommended way to edit the cron config, crontab -e or directly editing some file, e.g. with sudo vi?

Joshua Fox
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  • Please [edit] your question and clarify. What is the first crontab you show? And are you sure the second is what you see with sudo crontab -e? There shouldn't be a user field in that file. It looks like both lines you show are actually from /etc/crontab. What do you mean by "what cron actually does"? Cron will run everything it is told to run. And no, sudo crontab -e will show root's user-crontab, not yours. – terdon Feb 10 '22 at 11:35
  • I edited it (the first line had been "swallowed" by triple tilde. – Joshua Fox Feb 10 '22 at 11:54
  • Thank you. Does "everything it is told to run" include both the configurations above? – Joshua Fox Feb 10 '22 at 11:56
  • Thanks! So, the output of sudo crontab -e is wrong, only /etc/crontab should have a user as the 6th field, so the line should be 13 0,12 * * * sleep 1347 && certbot renew -q. – terdon Feb 10 '22 at 11:57
  • "are you sure the second is what you see with sudo crontab -e?" Yes, I just retried. "There shouldn't be a user field" This is a simple default-configured Google Compute Engine VM, I am logged in as a user joshua, but note that sudo does not require entering a password – Joshua Fox Feb 10 '22 at 11:57
  • "sudo crontab -e will show root's user-crontab, not yours." OK, so what is the difference between these two configurations? – Joshua Fox Feb 10 '22 at 11:58
  • "the output of sudo crontab -e is wrong." OK, so that probably means that edited it-- wrongly. – Joshua Fox Feb 10 '22 at 11:59
  • crontab -e verifies your edits, refuses to install a crontab with errors, and signals the cron daemon that it should refresh its internal copy of the new file. vi crontab does none of those things, and is inviting disaster. Also, crontab -l will list your crontab file. Hint: crontab default editor is nano on my box -- EDITOR=vi crontab -e is my friend here. – Paul_Pedant Feb 10 '22 at 14:35
  • Thank you. So there is never a need to edit /etc/crontab – Joshua Fox Feb 10 '22 at 15:09

1 Answers1

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The commented lines in /etc/crontab will tell you:

# /etc/crontab: system-wide crontab
# Unlike any other crontab you don't have to run the `crontab'
# command to install the new version when you edit this file
# and files in /etc/cron.d. These files also have username fields,
# that none of the other crontabs do.

/etc/crontab and /etc/cron.d/* define the system-wide crons. They have a user field in front of the command to be executed.

With sudo crontab -e, you edit root's crontab file which is located at /var/spool/cron/crontabs/root (for debian, different location in other OS).

Note, that you should never edit the files directly, but use crontab -e command.

The user's crontab file should not include the user name, so it should read:

13 0,12 * * * sleep 1347 && certbot renew -q
terdon
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pLumo
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