There are quite a few workrounds on the Tails page for laptops with dual graphic adaptors, but none of them worked for me.
The ZBook seems to boot in Intel HD graphics and then switch to Radeon graphics on login.
The display is then only active for a few seconds before crashing to the boot text. All you can do then is press the power button to shut down.
Failsafe mode wasn't really acceptable as it seems to be software driven and was very slow, so, after a bit of experimentation I found hitting TAB on the Grub boot screen and appending 'radeon.modeset=0' (without the quotes) allowed Tails to boot into a stable, fast desktop. I know it's only using the Intel graphics now, but I don't think Tails needs the high power Radeon adaptor anyway.
I then tried to find a way to make this permanent.
After more experimentation I found that you could remount the boot media with a read-write flag and then change the appropriate .cfg files with:
- sudo mount -o remount,rw /lib/live/mount/medium
- sudo vi /lib/live/mount/medium/syslinux/liveamd64.cfg
- sudo vi /lib/live/mount/medium/EFI/BOOT/liveamd64.cfg
- sudo mount -o remount,ro /lib/live/mount/medium
To use use sudo, you need to set a password on boot with the 'More Options' dialog, and you have to append the 'radeon.modeset=0" manually the first time you boot to be able to do the above.