Command works fine in CLI but not in cron

Entropy1024 · 10-31-2015, 06:51 AM

The command I use to make a backup of the cron file is:

Code:

crontab -l > ~/readynas/Tim/IT/p5e/cron_$(date +%Y%m%d_%H%M).bak

Which when executed manually from the CLI generates a file called cron_20151031_1234.bak (depending on date & TOD of course) in the ~/readynas/Tim/IT/p5e folder. No issue whatsoever.
However when I put this in cron to execute this at midnight each night, nothing gets generated. extract from cron file below

Code:

# Backup Cron daily at midnight
0 0 * * * * crontab -l > ~/readynas/Tim/IT/p5e/cron_$(date +%Y%m%d_%H%M).bak

It's the exact same bit of code, but I am unsure why it's not being executed from the cron job. Do you know why this is not working please?

Kind regards
Tim

ondoho · 10-31-2015, 07:46 AM

all i know about cron is that it doesn't use $PATH, so you have to give absolute paths to everything.

i would change '~' to /home/yourusername and 'date' to '/usr/bin/date' (although date is possibly located elsewhere).

Entropy1024 · 10-31-2015, 10:11 AM

Quote:

Originally Posted by ondoho

all i know about cron is that it doesn't use $PATH, so you have to give absolute paths to everything.

i would change '~' to /home/yourusername and 'date' to '/usr/bin/date' (although date is possibly located elsewhere).

Thanks for the reply. It did not fix the issue unfortunately. Perhaps I can copy the file itself, do you know where it is stored?

Many thanks
Tim

Emerson · 10-31-2015, 10:22 AM

First, cron does not log in, thus there are no environment variables set for it, it certainly is not aware of your user environment. Thus the need to use full paths. Second, for the very same reason it will not be able to access remote shares by default.

michaelk · 10-31-2015, 11:17 AM

Check out the gotchas in the following link. Should help you find the answer to your problem.
http://www.pantz.org/software/cron/croninfo.html

A users crontab does have a very limited default environment but can be changed easily. For example:

Quote:

HOME=/home/user
LOGNAME=user
PATH=/usr/bin:/bin
LANG=en_US.UTF-8
SHELL=/bin/sh
PWD=/home/user

Entropy1024 · 10-31-2015, 11:46 AM

Quote:

Originally Posted by michaelk

Check out the gotchas in the following link. Should help you find the answer to your problem.
http://www.pantz.org/software/cron/croninfo.html

A users crontab does have a very limited default environment but can be changed easily. For example:

OK great thanks. Got it working now. Was an interesting issue. Good to find out why it was not playing ball.