Debian – Dropbear terminates before LUKS password prompt on Debian Jessie

I got this same problem a few weeks ago (Debian Wheezy 7.6) and after some days of troubleshooting I found out that there was a config file missing which was preventing to the cryptroot script on init-top to run correctly, hence it was not stopping to ask the password via ssh, killing the dropbear at the end of the sequence (init-bottom).

The config file is called cryptroot and should be under /etc/initramfs-tools/conf.d/ If I am not mistaken that config file should have been created automatically during install (I have read just one tutorial talking about that config file) but somehow it did not (tested in a physical server and in a VM, same OS and versions)

It took me a couple of tries to configure it properly, since I could not find the proper syntax at that time. My cryptroot config file is as follows:

target=crypt-root,source=/dev/vg0/root,lvm=root

Once created the config file just update the initramfs and try again:

update-initramfs -u

You need to add that script to your initramfs. On Debian (I suspect Mint is the same), it appears that the password prompt comes from /usr/share/initramfs-tools/scripts/local-top/cryptroot. That script arranges itself to be called last out of the local-top scripts. There is a parallel set of directories in /etc intended for local customization. So you just need to plop a file that looks something like:

#!/bin/sh
PREREQ=""
prereqs()
{
     echo "$PREREQ"
}

case $1 in
prereqs)
     prereqs
     exit 0
     ;;
esac

echo 50 > /sys/class/backlight/acpi_video0/brightness

into either /etc/initramfs-tools/scripts/local-top or /etc/initramfs-tools/scripts/init-premount. The file name doesn't matter, though I'd pick something like local-backlight-brightness to make sure it doesn't conflict with some package-provided script. (The prereqs boilerplate comes straight from the initramfs-tools manpage.)

Then, run update-initramfs -u.