Failing to install Stretch on QNAP TS-420

[Mark Duggan <mduggan@gmail.com>]

In attempting to install Stetch on QNAP TS-420 I seem to fail at the same step every time. At the end of the "Installing the base system" the installer fails to install a kernel and throws the error message "No installable kernel was found in defined APT sources". There is some further text about installing a kernel manually later, but that that is recommended for experts etc.

Here's what is showing in the logs just before the issue is encountered.

Feb 18 19:43:16 base-installer: warning: apt update failed: 139

Feb 18 19:43:18 in-target: Reading package lists...

Feb 18 19:43:18 localechooser: error: the command 'validlocale' is not available

Feb 18 19:43:23 base-installer: info: Found kernels ''

I've tried continuing but it hits other issues later, which I'm not sure but presume are related to this

Any insight on how to fix this or even if I can increase the debugging level would be useful

Thanks

Mark