NFS in Docker: exportfs: <path> does not support NFS export

I'm working on a docker NFS container, but running into trouble mounting the exported directories (even on localhost).

The problem

exportfs: <path> does not support NFS export

The setup

My container uses an entrypoint script to

• write directories (provided via command-line arguments) into /etc/exports,
• invokes rpcbind and service nfs-kernel-server start, and
• defers to inotifywait to remain running.

The Dockerfile is nothing special. I install inotify-tools and nfs-kernel-server, expose port 2049, and copy over the entrypoint script.

I'm using docker-machine on an El Capitan Macbook.

I map volumes from the host into the container to give the nfs server access to directories that I want to export.

Entrypoint script

modprobe nfs
modprobe nfsd

for x in ${@}; do
   echo -e "$x\t*(rw,sync,no_subtree_check,crossmnt,fsid=root,no_root_squash)" >> /etc/exports
done

source /etc/default/nfs-kernel-server
source /etc/default/nfs-common

rpcbind
service nfs-kernel-server start

exec inotifywait --monitor /exports

Debugging

Here's the setup for what I am trying to export.

%> ls $HOME/mounts
a
%> ls $HOME/mounts/a
asdf

Here's how I start the server.

%> docker run --privileged --rm --name=nfs-server --volume=$HOME/mounts/a/:/exports/a docker-nfs-server /exports/a
Exporting directories for NFS kernel daemon...exportfs: /exports/a does not support NFS export
.
Starting NFS kernel daemon: nfsd mountd.
Setting up watches.
Watches established.

And here's the debugging I've been doing while the container is running.

%> docker exec -it nfs-server bash
root@6056a33f061e:/# ls /exports
a
root@6056a33f061e:/# ls /exports/a
asdf
root@6056a33f061e:/# showmount -a
All mount points on 6056a33f061e:
root@6056a33f061e:/# exportfs -a
exportfs: /exports/a does not support NFS export
root@8ad67c951ecd:/# mount
none on / type aufs (rw,relatime,si=3ca85db062268b32,dio,dirperm1)
proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)
tmpfs on /dev type tmpfs (rw,nosuid,mode=755)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=666)
mqueue on /dev/mqueue type mqueue (rw,nosuid,nodev,noexec,relatime)
sysfs on /sys type sysfs (rw,nosuid,nodev,noexec,relatime)
tmpfs on /sys/fs/cgroup type tmpfs (rw,nosuid,nodev,noexec,relatime,mode=755)
cgroup on /sys/fs/cgroup/cpuset type cgroup (rw,nosuid,nodev,noexec,relatime,cpuset)
cgroup on /sys/fs/cgroup/cpu type cgroup (rw,nosuid,nodev,noexec,relatime,cpu)
cgroup on /sys/fs/cgroup/cpuacct type cgroup (rw,nosuid,nodev,noexec,relatime,cpuacct)
cgroup on /sys/fs/cgroup/blkio type cgroup (rw,nosuid,nodev,noexec,relatime,blkio)
cgroup on /sys/fs/cgroup/memory type cgroup (rw,nosuid,nodev,noexec,relatime,memory)
cgroup on /sys/fs/cgroup/devices type cgroup (rw,nosuid,nodev,noexec,relatime,devices)
cgroup on /sys/fs/cgroup/freezer type cgroup (rw,nosuid,nodev,noexec,relatime,freezer)
cgroup on /sys/fs/cgroup/net_cls type cgroup (rw,nosuid,nodev,noexec,relatime,net_cls)
cgroup on /sys/fs/cgroup/perf_event type cgroup (rw,nosuid,nodev,noexec,relatime,perf_event)
cgroup on /sys/fs/cgroup/net_prio type cgroup (rw,nosuid,nodev,noexec,relatime,net_prio)
cgroup on /sys/fs/cgroup/hugetlb type cgroup (rw,nosuid,nodev,noexec,relatime,hugetlb)
/dev/sda1 on /exports type ext4 (rw,relatime,data=ordered)
Users on /exports/a type vboxsf (rw,nodev,relatime)
/dev/sda1 on /etc/resolv.conf type ext4 (rw,relatime,data=ordered)
/dev/sda1 on /etc/hostname type ext4 (rw,relatime,data=ordered)
/dev/sda1 on /etc/hosts type ext4 (rw,relatime,data=ordered)
shm on /dev/shm type tmpfs (rw,nosuid,nodev,noexec,relatime,size=65536k)
nfsd on /proc/fs/nfsd type nfsd (rw,relatime)

What I know

Less than Jon Snow. I can identify a few variables that might each be responsible for my problem, but I don't know how to verify any of them:

• $HOME/mounts/a is on an OSX filesystem
• That filesystem is encrypted
• /exports/a is being mounted into the docker-machine VM

I don't have enough experience with NFS to know how to debug this effectively. Any assistance or information would be appreciated.

Update

It works in Parallels!

%> docker run --privileged --rm --name=nfs-server --volume=$HOME/mounts/a/:/exports/a docker-nfs-server /exports/a
%> docker exec -it nfs-server bash
root@3786d888f039:/# mkdir --parents /imports/a
root@3786d888f039:/# mount --types nfs --options nolock,proto=tcp,port=2049 localhost:/exports/a /imports/a
root@3786d888f039:/# ls /imports
a
root@3786d888f039:/# ls /imports/a
root@3786d888f039:/# ls /exports
a
root@3786d888f039:/# ls /exports/a
root@3786d888f039:/# touch /exports/a/asdf
root@3786d888f039:/# ls /exports/a
asdf
root@3786d888f039:/# ls /imports/a/
asdf

So that narrows down the problem to OSX/docker-machine or maybe even the encrypted filesystem on OSX.