Use a Debian DVD iso as an upgrade source
Posted on 2025-08-17
When relying on Free/libre software, and the services provided by those projects, I try not to be a bother. I download distros using torrents, and seed when I can. So when they released Debian Trixie, I realized I have a lot of Debian machines to upgrade, and that would require hitting the Debian repositories an awful lot. Unless...
I had already downloaded the Debian Trixie DVD ISO via bittorrent. I knew that
installing Debian via a DVD image usually added a line to
/etc/apt/sources.list for the CD itself. It begs the question, could I use the
ISO image I downloaded as a repository for the upgrade?
...yes. Yes, you can. First, you need to mount the ISO file locally:
mkdir /tmp/debian_iso
sudo mount -o loop path/to/debian.iso /tmp/debian_iso
The next step is to add the mounted directory to /etc/apt/sources.list.
Replace "trixie" with the release name represented by the DVD ISO:
deb [trusted=yes] file:///tmp/debian_iso trixie main contrib
You need the trusted=yes option to prevent signing issues from blocking your
upgrade. Leave all of the main source listings as they are; apt will know enough
to pull packages from the DVD if possible, or download upgraded versions if they
are available. You can perform the upgrade as normal, and simply comment out the
DVD source line once you've finished.
Thanks to the following resources that helped me find the required pieces to get this working:
- "Debian Upgrading from an ISO File" by Warlord
- Prathu Baronia's answer to "Force update from unsigned repository" on StackOverflow