Install: apt-get

Hi there,
I have a WD My Cloud PR4100 and I want it to back up using CrashPlan
I’ve seen Guide Installing CrashPlan but having trouble with apt-get. (in order to get java)
I get the following response:-sh: apt-get: not found

How do I install apt-get?

I think I need this, but not too sure on how to install as I’m having problems?
https://packages.debian.org/jessie/apt

Hello,

I’ve never tried this. Let’s see if an experienced user can comment on this.

I sure hope so!