Unable to boot freshly installed Byzantium on Macbook

I have a 2013 MacBookAir on which I used to co-habitate MacOS and Ubuntu. MacOS was on the 1st partition (followed by Mac Recovery partition), then there were the two Ubuntu partitions: boot and root filesystems (LUKs encrupted). It worked nicely: by holding the Option key at turn-on it was possible to select either MacOS or Ubuntu. It was also possible to set which one will boot by default.

That Ubuntu has long gone, and the Mac has long been used for MacOS only.

But now I want to get back to the same original dual-boot scheme but with PureOS instead of Ubuntu. So I sized the MacOS partition (at the start of the disk) down to leave plenty of space for PureOS, put the last PureOS live image on a USB stick, booted it and started installation. Selected the big empty partition for PureOS, set LUKs encryption.

It all went fine until the last step: where the black screen tells us to eject the installation media and press Enter, I did so, and saw an endless stream of error messages like this:

SQUASHFS error: Unable to read page/data ...

Those errors didn’t seem to be ending, so I just turned the machine off. And started trying to boot the fresh installation.

It starts booting seemingly fine: opens the encrypted disk, shows the blue screen with the list of kernel options, then the usual PureOS grey progress bar on black background. But eventually it falls into the dreadful BusyBox (initramfs) console.

After typing exit and hitting Enter I see:

Gave up waiting for root file system device. Common problems:
ALERT: /dev/mapper/luks-............. does not exist. Dropping to a shell!

What can possibly be wrong? Why would the rootfs LUKs device be missing?

For fault isolation it may make sense to see whether you can reinstate Ubuntu.

I’ve managed to resolve this. The key was to choose “Manual partitioning” (instead of “Replace a partition”) and create just one encrypted root partition without creating a separate one for /boot.

Otherwise the “Replace a partition” option will create two new encrypted partitions: one for /boot, another for /. The latter didn’t seem to unlock during boot, only the former.

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