Shell script not running with Cron, but runs manually

Question

I feel like I have tried everything, my search history is about 20 pages deep on google trying to fix this and nothing works. Basically I have a script that checks if my tun0 interface exists, and if it is missing, the computer will restart. Here's the code:

#!/bin/bash
. /etc/profile
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
if echo `ifconfig` | grep -q "tun0"
then echo ""
else
    reboot
fi

The script itself runs fine if I invoke it at a terminal using its path:

/scripts/vpnrestart1.sh

I've added this at the top of crontab -e:

SHELL=/bin/bash
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

My cron task looks like this:

* * * * * /scripts/vpnrestart1.sh

Permissions are all fine on the script itself and it can be executed without using sudo. As I mentioned, it runs from the terminal just fine and works as designed. But if I put it in cron and remove the tun0 interface, nothing ever happens.

Answer 1

Have you ever try debugging your script to see what happens when executed by cron? Insert below code into your script:

# log stdout and stderr to two different files
exec >>/var/log/looog.log 2>>/var/log/looog.err.log

# ...and log every command we try to execute to stderr (aka looog.err.log)
set -x

Once you script is executed those two files will be generated and you will be able to see what is happening.

Answer 2

If running reboot directly as a non-root user works when you're logged in, it's because your system is configured to allow users who are physically logged in to reboot the system. This works via Polkit.

From a crontab, you aren't in a logged-in session. A cron job that reboots the system would have to run as root.

I don't think rebooting is the solution to create a network interface. Just call whatever you do normally to bring up the VPN. And you'll probably need to be root to do that (you need to be root to set up a network interface, so either vpnrestart1.sh must run as root, or it gets root permissions via a setuid program such as sudo for the critical parts, or it delegates to NetworkManager which may use Polkit to allow some user sessions to affect the system configuration).

Answer 3

Use full path instead of relative path in your shell script. This solved my issue.