NFS client fails with “Protocol not supported” even though the protocol is listed as available

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NFS client fails with “Protocol not supported” even though the protocol is listed as available – Managing your servers can streamline the performance of your team by allowing them to complete complex tasks faster. Plus, it can enable them to detect problems early on before they get out of hand and compromise your business. As a result, the risk of experiencing operational setbacks is drastically lower.

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I set up an NFS serve for Proxmox to remotely backup VM images there. For some reason the Proxmox box won’t connect to the NFS server. I tested connecting with another the NFS client on a different server and it worked fine. I’m not sure what’s wrong because as far as the client’s commands say, it does support these connection types (version 3 and 4). I’m not sure what I’m missing here.

IPs replaced with SERVER_IP and CLIENT_IP for simplicity

List of mounts:

root@client:~# showmount SERVER_IP -e
Export list for SERVER_IP:
/export/backups CLIENT_IP/32
/export         CLIENT_IP/32

List of supported protocols:

root@client:~# rpcinfo -p SERVER_IP | egrep "service|nfs"
   program vers proto   port  service
    100003    3   tcp   2049  nfs
    100003    4   tcp   2049  nfs
    100003    3   udp   2049  nfs
    100003    4   udp   2049  nfs

Trying to mount the remote export:

root@client: mkdir -p /nfs/backups
root@client:~# mount SERVER_IP:/export/backups /nfs/backups -vv
mount.nfs: timeout set for Wed Apr 27 17:55:34 2016
mount.nfs: trying text-based options 'vers=4,addr=SERVER_IP,clientaddr=CLIENT_IP'
mount.nfs: mount(2): Protocol not supported
mount.nfs: trying text-based options 'addr=SERVER_IP'
mount.nfs: prog 100003, trying vers=3, prot=6
mount.nfs: trying SERVER_IP prog 100003 vers 3 prot TCP port 2049
mount.nfs: prog 100005, trying vers=3, prot=17
mount.nfs: trying SERVER_IP prog 100005 vers 3 prot UDP port 38873
mount.nfs: mount(2): Protocol not supported
mount.nfs: Protocol not supported

My /etc/exports on the server:

/export CLIENT_IP/32(rw,sync,no_subtree_check,sec=sys,fsid=0)
/export/backups CLIENT_IP/32(rw,sync,no_subtree_check,all_squash,anonuid=1010,anongid=1010)

/export/backups is mount --rbind /home/backups /export/backups. 1010 is the uid and gid for the backups user.

The only edited setting in /etc/conf.d/nfs:

OPTS_RPC_NFSD="8 -N 2 -V 3 -V 4 -V 4.1"

Does anyone have any ideas? Thanks in advance.

Solution :

Reboot server as per Zacq’s comment

Not the solution anyone wants to hear on a production Proxmox server, but it works. There must be an /etc/init.d/[something] restart type fix.

Had exactly the same symptoms as OP.

In addition client was complaining in dmesg

nfsv3: disagrees about version of symbol nlmclnt_proc
nfsv3: disagrees about version of symbol nfs_alloc_client
nfsv3: disagrees about version of symbol nfs_access_zap_cache
nfsv3: disagrees about version of symbol nfs_submount
nfsv3: disagrees about version of symbol nfs_create_server
nfsv3: disagrees about version of symbol nfs_post_op_update_in$
nfsv3: disagrees about version of symbol nfs_mkdir
nfsv3: disagrees about version of symbol nfs_get_client
nfsv3: disagrees about version of symbol nfs_file_operations
nfsv3: disagrees about version of symbol nfs_lookup
nfsv3: disagrees about version of symbol nfs_getattr
nfsv3: disagrees about version of symbol register_nfs_version
nfsv3: disagrees about version of symbol nfs_setattr
nfsv3: disagrees about version of symbol unregister_nfs_version
nfsv3: disagrees about version of symbol nfs_sops
nfsv3: disagrees about version of symbol nfs_link
nfsv3: disagrees about version of symbol nfs_try_mount
nfsv3: disagrees about version of symbol nfs_close_context
nfsv3: disagrees about version of symbol nfs_symlink
nfsv3: disagrees about version of symbol nfs_clone_server
nfsv3: disagrees about version of symbol nlmclnt_proc
nfsv3: Unknown symbol nfs_writeback_update_inode (err -22)
nfsv3: Unknown symbol nfs_dentry_operations (err -22)

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