The nfsd filesystem is a special filesystem which provides access to the
Linux NFS server. Writing to files in this filesystem can affect the server.
Reading from them can provide information about the server.
As well as this filesystem, there are a collection of files in the procfs
filesystem (normally mounted at /proc) which are used to control the NFS server.
The exportfs and mountd programs (part of the nfs-utils package) expect to find
this filesystem mounted at /proc/fs/nfsd or /proc/fs/nfs.