It seems that it has finally worked. I followed the procedure described at the end of my previous post.
Step A
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1. I booted with the installation media (it was not live cd, only for installation) and have chosen to quit installation when the relevant screen showed.
2. I then made a directory ...

Thank you for the reply. I'll follow your suggestion, when I get some space on my /dev/sda to make an "original" hard disk installation. I hope this will be in the next couple of days. Your explanation of the problem is the best I have read till now, but it doesn't explain why I can indeed boot the ...

I wonder if there is a kernel (eg the one used for the installation), which contains the needed modules. I suppose the kernel used after the installation is a mofified one, offering modules needed to boot from usb. Is there any other difference between this kernel and the finally installed one? I ...

OK, thanks, I'll temporarily follow your suggestion for creating the boot usb stick. This is of course an intermediate solution, it makes things easier, but it doesn't address the reason why my boot procedure fails. Anyway, I'll be happy not to be forced to build an initrd everytime I want to boot ...

But after a couple of days, previous behaviour returned. It ends with:
ERROR: could not insert 'ext4': Exec format error
..........
..........
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mount: mounting /dev/sdd10 on /mnt failed: No such file or directory
ERROR: No /sbin/init found on rootdev (or not mounted). Trouble ahead ...

I just repeated the initrd procedure, and booted again, for three consequential times. I hope this time it lasts, but I'm afraid it won't. In this case I'll come back.

Thanks.

I did exactly what is described in this forum post you refer me to (changing the partition name of course to suit my installation), albeit not from a hard drive installation, but from salix's live media (cd) as per gapan's suggestion. It worked the first, maybe also the second time, but then I ...

After successfully booting from usb, following the procedure described in following post:
http://forum.salixos.org/viewtopic.php?f=16&t=4941
(borrowed from another salixos forum post), I encountered a problem with booting the second, third etc times. I repeated the initrd procedure (essentially I ...

I'd rather use a live medium for this with a graphical environment, to have access to the instructions, since in both cases the kernel will be different and has to be specified. Thanks.

Yes, this seems to be the best way to do the fix. Since I chroot, then the salix kernel & modules will be used, so thank you for the sound reminder gapan. And I've found the relevant instructions for chrooting from the salix forum (used to do it all the time, but now I had forgotten ).