Debian Upgrade Buster To Bullseye

This article contains all problems that I encountered when upgrading Debian from 10/Buster to 11/Bullseye.

isc-dhcp-server failed to start

Unfortunately, all you see at first using systemctl status isc-dhcp-server is

Sep 30 20:51:28 host systemd[1]: isc-dhcp-server.service: Control process exited, code=exited, status=1/FAILURE
Sep 30 20:51:28 host systemd[1]: isc-dhcp-server.service: Failed with result 'exit-code'.
Sep 30 20:51:28 host systemd[1]: Failed to start LSB: DHCP server.

journalctl -xe contains relevant information:

Okt 01 09:22:26 host dhcpd[47376]: Server starting service.
Okt 01 09:22:28 host isc-dhcp-server[47361]: Starting ISC DHCPv4 server: dhcpd.
Okt 01 09:22:28 host isc-dhcp-server[47361]: Launching IPv6 server only.
Okt 01 09:22:28 host dhcpd[47388]: Wrote 0 NA, 0 TA, 0 PD leases to lease file.
Okt 01 09:22:28 host dhcpd[47388]: 
Okt 01 09:22:28 host dhcpd[47388]: No subnet6 declaration for vmnet (2001:0DB8::/32).
Okt 01 09:22:28 host dhcpd[47388]: ** Ignoring requests on vmnet.  If this is not what
Okt 01 09:22:28 host dhcpd[47388]:    you want, please write a subnet6 declaration
Okt 01 09:22:28 host dhcpd[47388]:    in your dhcpd.conf file for the network segment
Okt 01 09:22:28 host dhcpd[47388]:    to which interface vmnet is attached. **

The simple solution is to add the required subnet declaration in /etc/dhcp/dhcpd6.conf:

subnet6 2001:0DB8::/32 {
	range6 2001:0DB8::1 2001:0DB8::efff;
}

scanimage exits with "Out of memory" error

scanimage: open of device escl:http://127.0.0.1:60000 failed: Out of memory

It seems that version 1.0.31 has a bug that was fixed in 1.0.32, according to this bug report. Unfortunately, Debian only provides 1.0.31 to Debian 11 (there's no "updates" or "backports" package).

Providing scanimage in a chroot environment

mkdir bookworm
debootstrap --arch=amd64 bookworm bookworm/ https://deb.debian.org/debian/
mount -t proc proc bookworm/proc
mount -t devpts devpts bookworm/dev/pts
mount --bind /dev bookworm/dev
mount --bind /sys bookworm/sys
chroot bookworm/ /bin/bash --login
apt install locales
dpkg-reconfigure locales
LANG=en_US.UTF-8
echo "LANG=en_US.UTF-8" >> /etc/profile
apt install sane-utils