Thanks for the quick response.
I’m leaning towards a fresh install - i have several RPI’s that I would like to convert.
Is there a list of s/w compatibility/issues between Buster and Bullseye with the dietpi-software catalogue I can look through? You mentioned PHP - this would be a concern for me, so I’d like to look to what degree…
There should be no issue on a fresh install.
For an upgrade some smaller task might be needed.
if you have time, you could read true a full blown journey Stretch => Buster => Bullseye 
https://github.com/MichaIng/DietPi/issues/4511
I have given it a try on my raspberry pi 4
Started with a clone of my SD and made a backup in Dietpi including the userdata to an external drive.
Next i have run the commands on by on (as in this post, except for the mosquito .list as i do not use that). The only thing asked was if i would like to replace the Samba config file. The total proces was done in about an hour. Everything works fine for a day now, no issues found 
By running $ cat /etc/os-release in command-line, result is PRETTY_NAME=“Debian GNU/Linux 11 (bullseye)”
Software installed
│ [ ] 1 Samba Client: access SMB/CIFS/Samba network shares
│ [ ] 5 ALSA: Advanced Linux Sound Architecture
│ [ ] 6 X.Org X Server: aka X11 - X Window System implementation
│ [ ] 7 FFmpeg: Audio & video codec libary and programs
│ [ ] 17 Git: Clone and manage Git repositories locally
│ [ ] 25 Xfce: lightweight desktop
│ [ ] 41 Emby: web interface media streaming server
│ [ ] 50 Syncthing: backup and sync server with web interface
│ [ ] 67 Firefox: web browser for desktop
│ [ ] 73 Fail2Ban: prevents brute-force attacks with ip ban
│ [ ] 96 Samba Server: Feature-rich SMB/CIFS server
│ [ ] 103 DietPi-RAMlog: Makes /var/log a RAM disk, preserves file structure on reboot
│ [ ] 104 Dropbear: Lightweight SSH server
│ [ ] 115 Webmin: web interface system management
│ [ ] 117 PiVPN: openvpn/wireguard server install & management tool
│ [ ] 126 AdGuard Home: powerful network-wide ads & trackers blocking DNS server
│ [ ] 149 NZBGet: nzb download manager
│ [ ] 170 UnRAR: unarchiver for .rar files
│ [ ] 172 WireGuard: an extremely simple yet fast and modern VPN
│ [ ] 174 GIMP: mspaint on steroids
│ [ ] 195 youtube-dl: Download videos from YouTube and other video sites
great.
For someone running NextCloud, Owncloud or other web server based apps, additional task might be needed.
On my Pi 2B, I get these errors during apt update:
Err:2 https://packages.sury.org/php bullseye InRelease
The following signatures were invalid: EXPKEYSIG B188E2B695BD4743 DEB.SURY.ORG Automatic Signing Key <deb@sury.org>
Reading package lists... Done
W: GPG error: https://packages.sury.org/php bullseye InRelease: The following signatures were invalid: EXPKEYSIG B188E2B695BD4743 DEB.SURY.ORG Automatic Signing Key <deb@sury.org>
E: The repository 'https://packages.sury.org/php bullseye InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: Skipping acquire of configured file 'ui/binary-armhf/Packages' as repository 'https://archive.raspberrypi.org/debian bullseye InRelease' doesn't have the component 'ui' (component misspelt in sources.list?)
Did you update from Stretch directly or was it Buster before. You have an old PHP repository that was used on Stretch.
It is possible that system was upgraded from stretch. Anyway, I deleted it from sources.list, because dietpi-upgrade failed too after the upgrade to bullseye. After I deleted it, dietpi-upgrade worked again.
basically you could have fixed the repository https://github.com/MichaIng/DietPi/issues/4219
But it’s fine to have it removed as well.
Hello Joulinar, on given mqtt link bullseye file available now. please guide me step by step to upgrade my mqtt broker also to bullseye system. please guide me what thing i have to edit to deactivate old model (buster) & upgrade to newer model(bullseye) without any interruption. thanks
you are looking for the Mosquitto upgrade only? Rest of system is already on Bullseye?
i have followed the above procedure to migrate from buster to bullseye. all of my system works on bullseye. I think with this command
sed -i ‘s/bullseye/buster/’ /etc/apt/sources.list.d/mosquitto.list
we override the buster image off mqtt broker on bullseye system. as now bullseye component available for mqtt broker so we have to correct this command so that system will pick bullseye file.
basically just change the command and switch buster <> bullseye
sed -i 's/buster/bullseye/' /etc/apt/sources.list.d/*mosquitto*.list
apt update
apt upgrade
but it should be same version of mosquitto. They just added Bullseye repository without changes on mosquitto themselves
Thanks,
Hey guys, one of my Dietpi images is currently running on an Orange Pi Zero SBC (I followed these steps: https://github.com/MichaIng/DietPi/issues/1285#issue-280771944), but I’m not sure if the upgrade from Buster to Bullseye is supported on that board.
I wanted to check with you just in case if the guide on the blog (https://dietpi.com/blog/?p=811) would work for manually upgrading the system before doing anything.
Thanks as usual!
usually the guide should work same as it is not specified for specific devices. However we are not able to test the process on all SBC available. Therefore we recommend to do a full backup of the system before. Best would be to clone the SD card.
Got it, I’ll try then. Thanks Joulinar 