cron table mailx caused empty content

Question

I'm using centos 7.0/6.5. The content of /etc/cron.hourly/mail.cron

#!/bin/sh
log=/var/log/mail.cron.log
echo "`hostname` `date`" >> $log 2>&1
mailx -s "test mail" [e-mail] < $log

The result of /var/log/mail.cron.log

myhost Mon Jul 28 11:01:01 CST 2014

But, I got a empty e-mail, with correct subject. So, I test this cron manually. I got the correct e-mail content.

myhost Mon Jul 28 11:01:01 CST 2014
myhost Mon Jul 28 11:30:29 CST 2014

Here is the related log /var/log/cron

Jul 28 11:01:01 myhost run-parts(/etc/cron.hourly)[24577]: starting mail.cron
Jul 28 11:01:02 myhost run-parts(/etc/cron.hourly)[24605]: finished mail.cron

I'm wonder how to debug this problem.

Answer 1

A few things to try.

1. !/bin/sh -xv

2. Try redirecting stderr with two greater than signs, 2>>&1 .

The first will give you step-by-step output of your script. I'd try it first without redirecting stderr to your log file. Cron should mail you a copy of the output. You can see exactly where it goes wrong.

The second. Maybe you have an error that's clobbering your stdout? (Probably not, it works as you have it in CentOS 6.5.)

You could also check for unprintable characters using cat.

cat -vet /etc/cron.hourly/mail.cron

Still another thing to try is to use absolute paths to your commands, /bin/echo instead of echo, /bin/date instead of date, /bin/hostname instead of hostname. (ymmv) Jim is absolutely correct in cron doesn't always use the exact environment as the same interactive user.

Answer 2

You are sure the cron job works, as per your comments - however, you have tested it manually running the job while you are logged-in. The thing is that the jobs ran by cron do not take into account the settings and environment variables you have with your current user, so you probably need to source the .bash_profile settings file for the user as a step prior to sending the email in your script.

Change your script to this:

#!/bin/sh
source $HOME/.bash_profile     # or whatever profile file or setting you are using
log=/var/log/mail.cron.log
echo "$(hostname) $(date)" >> $log
mailx -s "test mail" [e-mail] < $log

cron knows nothing about your shell - it is started by the system, so it has a minimal environment. If you want it to be able to find your programs or run utilities installed in your system, you have to let it know where those are in the first place, and you can do that by setting the .profile variables at the beginning of your script.

Some useful links:

• How can I run a cron command with existing environmental variables?
• Where can I set environment variables that crontab will use?
• Crontab Job Does NOT Get the Environment Variables Set in .bashrc File

Answer 3

I saw that you got some answers but not a clear working answer. What worked for me was to set the cron this way:

*/5 * * * * /fullpath/cron.sh | ( body="$(cat)"; if [[ -n $body ]]; then echo "$body" | mail -s "Cron script output" [e-mail]; fi)

this captures the output and sends it to mail without it I get an empty email even when running in a script. (thanks to colucix)