Debian: Move from buster (old testing) to bullseye (new testing)

Debian 10 “buster” was released and now it is “stable release”. Future “bullseye” release is now being developed and marked as “testing”. But we still stay on “buster” marked as “testing which is wrong.

See also: Debian: From stretch (old stable) to buster (new stable)

But in /etc/apt/apt.conf.d/99defaultrelease we have “testing” as our default release (If you have that file). This is why when apt update performed we can see the following error messages:

N: Repository 'http://ftp.uk.debian.org/debian buster InRelease' changed its 'Version' value from '' to '10.0'                                                                        
E: Repository 'http://ftp.uk.debian.org/debian buster InRelease' changed its 'Suite' value from 'testing' to 'stable'
N: This must be accepted explicitly before updates for this repository can be applied. See apt-secure(8) manpage for details.
Do you want to accept these changes and continue updating from this repository? [y/N]

It’s time to switch to new “bullseye” development branch. Open /etc/sources.list:

sudo apt edit-sources
# OR open sources.list directly:
nano /etc/apt/sources.list

We should see something like that:

deb http://ftp.uk.debian.org/debian/ buster main contrib non-free
deb-src http://ftp.uk.debian.org/debian/ buster main contrib non-free

deb http://security.debian.org/debian-security buster/updates main
deb-src http://security.debian.org/debian-security buster/updates main

Replace “buster” with “bullseye” and “bullseye-security” for security updates. Now it should look like the following way:

deb http://ftp.uk.debian.org/debian/ bullseye main contrib non-free
deb-src http://ftp.uk.debian.org/debian/ bullseye main contrib non-free

deb http://security.debian.org/debian-security bullseye-security/updates main
deb-src http://security.debian.org/debian-security bullseye-security/updates main

Update the system package database. New package versions will be available:

sudo apt update

Now it is possible to install new packages.

If we want to make full upgrade of the system perform distribution upgrade. Stop all the programs that can write important (for you) information to the disk, some system applications will stop by apt:

sudo apt upgrade
sudo apt dist-upgrade

Reboot the system. The system will start with new versions of the kernel and services.

If we don’t want to upgrade the whole system, we can update one package (it contains codename and version of the system):

sudo apt update
sudo apt install base-files

Then lsb_release -a will output fresh information:

lsb_release -a
...
Distributor ID:	Debian
Description:	Debian GNU/Linux bullseye/sid
Release:	testing
Codename:	bullseye