Here is a list of known issues and bugs with Debian on QNAP TS-41x/TS-42x:
Debian 10 (buster)
On QNAP devices with 1 GB of RAM (i.e. TS-420U, TS-421 and TS-421U), the installer fails because of a kernel issue. Messages in
BUG: Bad rss-counter stateand
Unhandled fault: external abort on linefetch. You can set the RAM size to 768 MB as a workaround.
The initramfs might not fit in flash. You can try to use XZ compression to make it fit.
There are some reports that LED lights don't work correctly on some QNAP models (they always show red).
There are some reports that Wake-on-LAN (WOL) no longer works.
There are problems setting the clock (RTC).
Debian 11 (bullseye)
- Debian 10 (buster) is the last release to support this device. There's no support in Debian 11 (bullseye).