Comment # 13 on bug 1188110 from Ignaz Forster

I see the problem now: Transaction->getRoot() returns the path to the directory
of the root file system. This path is then set as the root path for DNF
directly.

The problem is that /usr/sbin/grub2-install requires to have a dedicated mount
point and not just a directory, so tukit is also creating a temporary bind
mount and executes commands it receives on that bind mount instead of the root
directory. However libdnf-plugin-txnupd is using the root path directly.

I guess the best solution would be to return the bind path for
Transaction->getRoot() instead. If one needs the real root path one can use
Snapshot->getRoot() then (the Snapshot class will become public with
transactional-update 4.0 anyway).