How to fix a Solaris boot archive

After an update it might happen, that the bootarchive is invalid/damaged. To fix this, boot into the failsafe mode (usually second option in GRUB) and let the system automatically repair it. If that is not offered or unsuccessfull, mount the old root partition to /a (usually offered by the system) and run

bootadm update-archive -vR /a

Then reboot (or umount /a and then reboot)

If that does not help, the system might need to recreate the boot archive from scratch:

cd /a/platform/i86pc/
mv boot_archive boot_archive.disable
bootadm update-archive -vR /a
umount /a

and again reboot the system - usally that is all it takes.