Debian – What shell is used by cron

crondebian

cron runs shell commands from crontabs.

But having just got caught out by the differences between zsh and bash, I'm now concerned that I don't know which shell cron uses to interpret crontab commands? Obviously the simple case where the cron entry just points to a script file is handled by the #!/path/to/interpreter on the first line, but what when you have something more complex in cron?

I looked in /etc/cron* and can't see anything that might allow this to be set or changed?

Best Answer

You can put SHELL=/bin/bash in your crontab - you can also point to a .bashrc using BASH_ENV="/root/.bashrc". That should get you going. I actually don't know what happens if you don't have SHELL defined, but adding it to crontab makes it easy to tell what is what.

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Linux – bash script returns “out of memory” in cron, but not in shell

Even though limits.conf is commented out, I suggest that you test just to make sure. One way would be to create a cronjob that just contains something like "ulimit -a | Mail -s 'limits' me@example.com" to have the info emailed to you. Once you know what the limits are, then you can just reset them in the shell script that actually runs the rsync:

#!/bin/bash
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Bash – Problem using BASH in cron (FreeBSD)

A few things occur to me while reading this.

If you are running bash echoing the value of $BASH should expand to the full path and filename of the bash executable in use.

How are you calling date in your script. Are you calling it with the full path name or as "date". The later case can result in the use of function, aliases, or whatever happens to be first in the path rather than the date program you expect.

Bash will behave differently in some cases depending on the environment. You may want to dump the environment to a file from the script and look at it running from the command-line and from cron. You may find that the PATH is different or that some other environment variable is set differently. You should be able to dump this to a file in /tmp by putting a line like "env > /tmp/environment.$$" in the script. Each time the script is run it will print out the environment to a file named environment.(pid of script)

You can set also the shell for the entire crontab to whichever shell you want by using "SHELL=/path/to/new/shell" on a line by itself.

Best Answer

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