Linux – Is it bad to edit cron file manually

cronlinuxscheduled-task

It is usually instructed to introduce new cron jobs through command lines; but I found it easier (with a better control of current cron tasks) to manually edit (in text editor) the user cron file like /var/spool/cron/crontabs/root.

Is it dangerous to edit the file in text editor?

The comments in the default file is confusing. The first line says

# DO NOT EDIT THIS FILE - edit the master and reinstall.

But the fourth line says

# Edit this file to introduce tasks to be run by cron.

Best Answer

If you modify the user file under crontabs, it should work. However, there are two issues to take into consideration:

If you mistyped the cron entry in the file, you will not be warned as opposed to using crontab -e command.
You can not edit your user file under crontabs directly without login as root or using sudo. You will get permission denied error.

Edit

One more point to add. When you edit the file directly, you may be warned by the text editor if you opened the file twice (two users accessing the same file). However, the cron list will be overwritten when using crontab -e from two different shell sessions of the same user. This is another difference.

Related Solutions

Cron Job – How to Run a Cron Job Manually and Immediately

Here's what I did, and it seems to work in this situation. At least, it shows me an error, whereas running from the command line as the user doesn't show the error.

Step 1: I put this line temporarily in the user's crontab:

* * * * *   /usr/bin/env > /home/username/tmp/cron-env

then took it out once the file was written.

Step 2: Made myself a little run-as-cron bash script containing:

#!/bin/bash
/usr/bin/env -i $(cat /home/username/tmp/cron-env) "$@"

So then, as the user in question, I was able to

run-as-cron /the/problematic/script --with arguments --and parameters

This solution could obviously be expanded to make use of sudo or such for more flexibility.

Hope this helps others.

Bash – What’s the advantage of using a bash script for cron jobs

It depends on what you're doing with the job.

cron does not give you a real scripting environment, so, if you're doing something more complicated than simply calling a couple of commands, you probably want to use cron to call a script. You can also deal with things like variable expansion in a script, which can be difficult if not impossible to do in cron's environment.

The temporary file that you see when you run crontab -e is just that: a temporary file that will be cleaned up after you exit the editor session. The actual crontabs that you edit through this method wind up in /var/spool/cron.

Actually, since these are relatively basic unix-specific questions, there's the unix.stackexchange.com side of things, which may be more helpful.

Best Answer

Related Solutions

Cron Job – How to Run a Cron Job Manually and Immediately

Bash – What’s the advantage of using a bash script for cron jobs

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