exportfs returns error "does not support NFS export"

SUSE Linux Enterprise Server 15

A SLES system has one or more of the following file systems mounted:

1. CIFS share, mounted from another host.
2. NFS share, mounted from another host.
3. exfat file system, mounted from local disk.
4. ecryptfs file system, mounted from local disk.

Examples:

//big-storage/export_cifs on /export/e1/e2/cifs type cifs ... 
big-storage:/exports/big-nfs-server on /export/e1/from_big_nfs type nfs4 
/dev/mapper/export-exfat_export on /export/e1/exfat type exfat ...
/export/my_encrypted_files on /export/my_encrypted_files type ecryptfs ... 

Then, if an attempt is made to export any of these via NFS, an error is returned:

exportfs: <PATH> does not support NFS export

Specific to the attempt to reexport the NFS share, this message also appears:

exportfs: /export/e1/from_big_nfs/ requires fsid= for NFS export

NOTE:  Various versions of the linux kernel and or the exportfs command may react differently to these attempts.

Some file systems cannot be exported via NFS.  Additionally, even when the kernel may allow certain file systems to be exported, SUSE’s support organization may not support it.

For example, SUSE does not support "daisy chain" or "reexport" scenarios, where a mounted NFS or CIFS share is exported again via NFS or CIFS.  As a general rule, only export natively local file systems.  Even then, not every type of local file system is allowed to be exported.  For example, exfat and ecryptfs are not exportable.

As suggested by the “...requires fsid=...” message above, adding an fsid parameter to the export syntax may allow NFS reexport of an NFS mount to proceed.  However, there are still features of NFS which cannot function correctly in a reexport scenario, so SUSE does not officially support this practice.

Besides introducing potential for known limitations (aka malfunctions) to occur, reexporting typically doubles the number of failure points possible while using the NFS file system, and could introduce additional performance bottlenecks as well.

NFS export requires specific support from the underlying file system, including the ability to provide a filehandle for each file and to locate the file using that filehandle.  Not all file systems provide this necessary functionality, and attempting to export a file system without this support will result in the "does not support NFS export" error.  CIFS, in particular, lacks required NFS export functionality.

Despite the above explanation, lack of a “does not support NFS export” message only means that the attempt has passed certain criteria.  It does not guarantee that the export is fully supported in every way.

If issues are encountered while using an NFS reexport, reproducing the issue without reexport may be necessary before obtaining assistance (advice, analysis, troubleshooting, fixes) from SUSE.

If using SLES 15 SP6 (or newer), SUSE may be willing to investigate some issues that arise from NFS reexport of an NFS mount.  However, SUSE does not guarantee how far that investigation will go, nor that fixes will be provided.  This practice is not fully supported, and any efforts will be at SUSE’s sole discretion.

There is a Linux kernel community article which discusses the possibility but known limitations (malfunctions) of NFS reexports, at the link below. Keep in mind, however, that the list of limitations may not be complete.  Furthermore, that discussion is pertinent to very recent kernels.  Most enterprise Linux distributions contain less-recent kernels and may have additional limitations.

https://docs.kernel.org/filesystems/nfs/reexport.html