Appendix A. Managing your buster system before the upgrade

Basically this is no different from any other upgrade of buster you've been doing. The only difference is that you first need to make sure your package list still contains references to buster as explained in Section A.2, “Checking your APT source-list files”.

If you upgrade your system using a Debian mirror, it will automatically be upgraded to the latest buster point release.

If any of the lines in your APT source-list files (see sources.list(5)) contain references to “stable”, this is effectively pointing to bullseye already. This might not be what you want if you are not yet ready for the upgrade. If you have already run apt update, you can still get back without problems by following the procedure below.

If you have also already installed packages from bullseye, there probably is not much point in installing packages from buster anymore. In that case you will have to decide for yourself whether you want to continue or not. It is possible to downgrade packages, but that is not covered here.

As root, open the relevant APT source-list file (such as /etc/apt/sources.list) with your favorite editor, and check all lines beginning with deb http:, deb https:, deb tor+http:, deb tor+https:, URIs: http:, URIs: https:, URIs: tor+http: or URIs: tor+https: for a reference to “stable”. If you find any, change stable to buster.

If you have any lines starting with deb file: or URIs: file:, you will have to check for yourself if the location they refer to contains a buster or bullseye archive.

	Important
	Do not change any lines that begin with deb cdrom: or URIs: cdrom:. Doing so would invalidate the line and you would have to run apt-cdrom again. Do not be alarmed if a cdrom: source line refers to “unstable”. Although confusing, this is normal.

If you've made any changes, save the file and execute

# apt update

to refresh the package list.

Before upgrading your system to bullseye, it is recommended to remove old configuration files (such as *.dpkg-{new,old} files under /etc) from the system.