On Thu, Nov 02, 2023 at 04:56:59PM +0100, Martin wrote: > I have installed old distribution > # deb cdrom:[Debian GNU/Linux 9.1.0 _Stretch_ - Official amd64 DVD Binary-1 > 20170722-11:29]/ stretch contrib main non-free > (because that was newest distribution I had on DVD with me) > > I configured network and now I am trying to update the system to sid.
You *cannot* upgrade a Debian 9 system directly to current unstable. The current Debian release is Debian 12. In order to upgrade this system to unstable, you would first have to upgrade it to Debian 10, then to Debian 11, then to Debian 12, and then finally to unstable. I would not do that, however. Instead, I would reinstall the system using the Debian 12 installer, and then go from *there* to unstable, if for some reason you really truly need to run unstable. If you don't actually need to run unstable, just leave it on Debian 12.
