It is 100000 actually and even with 777 rights it still fails.

I might have to heed to your warnings. The nfs share is actually a mirror RAID hosted on an OMV VM on the same host. It would be just easier to spin up bookstack image on that VM itself. Thanks

That sounds a bit too convoluted for my needs. Even if it works, I am not sure if I will be able to maintain such a setup. But thanks for your inputs.

This is the case with bookstack image. I specify the uid and gid as environment variables and it is expected that the ids remain compatible with the lxc and the host. But I am having trouble writing to the mount even from the lxc with the uid 1000 which is mapped to 101000 on the host.