Docker fails to mount -v volume from NFS-mounted directory

Docker Engine General
23

Hi. I found that NFS shares with the following server config (/etc/exports) do not work:

*(rw,sync,no_subtree_check,no_all_squash)

while the ones with the following do:

*(rw,sync,no_root_squash,no_subtree_check)

RedHat does not recommend using the no_root_squash, however.

I think docker initially starts with the root user and tries to bind-mount the directories with that user (even when running docker run --user=$UID:UID -v /etc/passwd:/etc/passwd -v /etc/group:/etc/group). It then drops into the requested user (the one specified with the UID).

The initial mount however is always unsuccessful.

Update: Seems this comment says the same thing.

Update2 [Solution]:

This worked to access files on an NFS share with non-root Docker and *(rw,sync,no_subtree_check,no_all_squash) (user permissions enforced).

$ export NFS_VOL_NAME=mynfs
$ export NFS_LOCAL_MNT=/mnt/foo
$ export NFS_SERVER=bambam.local
$ export NFS_SHARE=/mnt/swap
$ export NFS_OPTS=vers=4,soft

$ docker run --rm -it --mount \
  "src=$NFS_VOL_NAME,dst=$NFS_LOCAL_MNT,volume-opt=device=:$NFS_SHARE,\"volume-opt=o=addr=$NFS_SERVER,$NFS_OPTS\",type=volume,volume-driver=local,volume-opt=type=nfs" \
  --user $UID:$UID -v /etc/passwd:/etc/passwd -v /etc/group:/etc/group \
  busybox ls $NFS_LOCAL_MNT

On the server:

$ cat /etc/exports
/mnt/swap *(rw,sync,no_subtree_check,no_all_squash)
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