How to Add Debian Stretch Repository on Debian-Based Systems

Setting Up Repo

2. 2. Adding Repo

   Then to Add Debian Stretch Repository
   Simply Copy and Execute this Command:

   (And in case of “su: Authentication failure” try instead with “sudo su“)

   su -c "echo 'deb http://ftp.fr.debian.org/debian stretch main' >> /etc/apt/sources.list.d/stretch.list"

   Finally, to Enable also the Contrib and Non-free Repos Instead:
   (And in case of “su: Authentication failure” try instead with “sudo su“)

   su -c "echo 'deb http://ftp.fr.debian.org/debian stretch main contrib non-free' >> /etc/apt/sources.list.d/stretch.list"

   Possibly Change the Debian Mirror in base of your Location

   Debian Ftp Mirror List

   Debian Servers Worldwide List

   Finally, Ctrl+x to Save & Exit from nano Editor :)

3. 3. Pinning Apt

   Then to make Apt Pinning Setup
   (Optional if you need to install only some Packages and after you disable it)
   And this is Fundamental to Preserve the Stability of the System in Case of Updates/Upgrades!
   So then Edit the Apt Preferences File with:

   sudo nano /etc/preferences

   And for a Debian Stable Based Distro Append:

   Package: *
   Pin: release n=stable
   Pin-Priority: 700
   
   Package: *
   Pin: release n=oldstable
   Pin-Priority: 600
   

   Now you can Freely use both synonyms ‘oldstable‘ or ‘stretch‘ on the Setup.
   The same also in All other cases and so again with ‘stable‘/’buster‘.
   Instead, for a Debian Testing Based Distro:

   Package: *
   Pin: release n=testing
   Pin-Priority: 700
   
   Package: *
   Pin: release n=oldstable
   Pin-Priority: 600
   

   Finally, for Kali Rolling:

   Package: *
   Pin: release n=kali-rolling
   Pin-Priority: 700
   
   Package: *
   Pin: release n=oldstable
   Pin-Priority: 600
   

   Ctrl+Shift+v to Paste in Code.
   And finally, Ctrl+x to Save & Exit from nano.
   Possibly to Find What’s your actual Repo Base use the cat Command like:

   cat /etc/apt/sources.list

   Or again look into the sources Directory to find out eventual others Repos:

   cat /etc/apt/sources.list.d/*.list

4. 4. Enabling Repo

   Finally, to Re-Load Repositories
   Do:

   sudo apt update

5. 5. Installing Single Package

   Finally, to Install One Package from Stretch Repo
   Execute:

   sudo apt -t unstable install [MYCOOLPACKAGE]

   So for instance:

   sudo apt -t unstable install libgconfmm-2.6-1v5