SAGA installation in QGIS 2.8 on debian linux

I install QGIS 2.8 in debian (linux) through nightly jessie (qgis testing) and I see that SAGA is not in processing toolbox, so I install saga gis software but still it doesn't appear in processing.

How do I run SAGA in processing toolbox?

UPDATE:

This problem is resolved through the line commands:

sudo add-apt-repository ppa:johanvdw/saga-gis

sudo apt-get update

sudo apt-get install saga

But in my case (Debian Jessie) instead of sudo add-apt-repository ppa:johanvdw/saga-gis I went to http://ift.tt/18GN7UA and in Technical details about this PPA I choose Trusty version, copy the lines and paste in sources.list. It works!!!