Why won't this shutdown shell script work under root's crontab when the guest user is logged in? [closed]

Question

I've got a laptop running Lubuntu 13.04 and guest account enabled. People forget to shut it down every day so I figured I'd just put a one line script into root's cron to solve that. No dice. It shows up in the syslog every day like it ran, but the computer doesn't turn off. Is it not possible for root to shutdown the machine when another user (not in wheel) is logged in?

Shell script:

#!/bin/bash
shutdown -h now

Line in root's crontab:

34 18 * * * /root/shutdownDaily.sh

The script is executable:

-rwxr-xr-x 1 root root 28 Sep 9 17:47 shutdownDaily.sh*

Answer 1

"/sbin" is not in default cron PATH. So you need to add it there.

you can check it with:

*/2 * * * * /bin/echo "$PATH" > /home/myuser/my.log

Result:

[root@localhost vagrant]# cat my.log 
/usr/bin:/bin

Also you can see it in the mail headers sent by cron:

Content-Type: text/plain; charset=UTF-8
Auto-Submitted: auto-generated
X-Cron-Env: <SHELL=/bin/sh>
X-Cron-Env: <HOME=/root>
X-Cron-Env: <PATH=/usr/bin:/bin>
X-Cron-Env: <LOGNAME=root>
X-Cron-Env: <USER=root>