I was testing a new instance of Debian Jessie with a new cloud provider scaleway and was struggling to find the issue why one of the bash script is not running on the startup
Digging through the /var/messages log I noticed the following error
Oct 28 13:20:37 sky net.agent: ERROR: /sbin/ifup not found. You need to install the ifupdown package.
Which gave me a hint then I tried
apt-get install ifupdown
and voila the script started working
Maybe this post will help someone