Notes on Debian's sources.list
written March 17, 2025 by Time Traveler
Category: BlogEntry Tags: Debian; apt; sources.list; package management;    #58
 

We had a question from a customer regarding what happens after you do a full install of Debian from the Debian USB Complete Collection.

If you don't do anything but step throught the install, your /etc/apt/sources.list looks something like this like this:

deb cdrom:[Debian GNU/Linux 12.9.0 _Bookworm_ - Official amd64 DVD Binary-1 with firmware 20250111-10:55]/ bookworm contrib main non-free-firmware

If you boot the installed OS from your hard drive, and try to update/install any packages, you'll get a warning about the missing disc. If wish to use the USB for updates and your source (repository) for your pacakges, you want to use the mountusb.sh script in the USB_Boot/boot/mountusb folder. Refer to the notes, details, and links below (section labeled "Running without internet, want to use packages on USB").

However, if you want to use the internet for updates going forward, you will need to change the soures.list file

For a good discussion, overview, and examples, you can see the Debian wiki:

Debian SourcesList (info on the /etc/apt/sources.list)

About 40% down the page, you'll find the actual text you want for updates of both Debian and the Debian source. Note you can skip the deb-src lines if you will not want any source code updates.

deb https://deb.debian.org/debian bookworm main non-free-firmware
deb-src https://deb.debian.org/debian bookworm main non-free-firmware

deb https://security.debian.org/debian-security bookworm-security main non-free-firmware
deb-src https://security.debian.org/debian-security bookworm-security main non-free-firmware

deb https://deb.debian.org/debian bookworm-updates main non-free-firmware
deb-src https://deb.debian.org/debian bookworm-updates main non-free-firmware


Example (as super user/root user at the command prompt):

cd /etc/apt
nano sources.list
-or-
kate sources.list
-or-
gedit sources.list
-or-
YourFavoriteTextEditor sources.list

Comment out the existing line, add a comment, and you get:

#Commented out, use internet sources below
#deb cdrom:[Debian GNU/Linux 12.9.0 _Bookworm_ - Official amd64 DVD Binary-1 with firmware 20250111-10:55]/ bookworm contrib main non-free-firmware

deb https://deb.debian.org/debian bookworm main non-free-firmware
deb-src https://deb.debian.org/debian bookworm main non-free-firmware

deb https://security.debian.org/debian-security bookworm-security main non-free-firmware
deb-src https://security.debian.org/debian-security bookworm-security main non-free-firmware

deb https://deb.debian.org/debian bookworm-updates main non-free-firmware
deb-src https://deb.debian.org/debian bookworm-updates main non-free-firmware


Save these change, return to command line, and then run apt update

Running without internet, want to use packages on USB