Ubuntu 16.04 nfs-kernel-server won't start

Question

After a system reboot, nfs-kernel-server was inactive. When I try to start I get

nfs-server.service: Job nfs-server.service/start failed with result 'dependency'.

which is echoed in journalctl -xe. I am using Ubuntu 16.04.2. Tried a reinstall, and received the same message.

The only flag I can see is that a

systemctl list-dependencies nfs-kernel-server

gives nfs-mountd.service as failed, while

systemctl list-dependencies nfs-mountd.service

shows nfs-server.service as failed.

Output of systemctl status:

nfs-server.service - NFS server and services
Loaded: loaded (/lib/systemd/system/nfs-server.service; enabled; 
vendor preset: enabled)
Active: inactive (dead)

while when I try to start the service (journalctl -f),

Failed to start NFS Mount Daemon
Dependency failed for NFS server and services.
nfs-server.service: Job nfs-server.service/start failed with result 
'dependency'.

Answer 1

Is your Ubuntu server a linux container (lxc) ?

If yes, you need to set something like explained here:

mount fstype=rpc_pipefs, mount fstype=nfsd,

Answer 2

Ubuntu 20.04

My file /etc/exportfs had an entry to export a not mounted mount point. Deleting that entry followed by the commands exportfs -rav | sort; service nfs-kernel-server restart; solved the problem.