Ubuntu Manpage: nfsref - manage NFS referrals

Provided by: nfs-kernel-server_2.8.2-2ubuntu1_amd64

NAME

       nfsref - manage NFS referrals

SYNOPSIS

       nfsref [-?d] [-t type] add pathname server export [ server export ... ]

       nfsref [-?d] [-t type] remove pathname

       nfsref [-?d] [-t type] lookup pathname

INTRODUCTION

       NFS version 4 introduces the concept of file system referrals to NFS.

       A  file  system referral is like a symbolic link (or, symlink) to another file system share, typically on
       another file server.  An NFS client, under the server's direction,  mounts  the  referred-to  NFS  export
       automatically when an application first accesses it.

       NFSv4  referrals  can  be  used  to  transparently  redirect clients to file systems that have been moved
       elsewhere, or to construct a single file name space across multiple file servers.  Because  file  servers
       control the shape of the whole file name space, no client configuration is required.

DESCRIPTION

A junction is a file system object on an NFS server that, when an NFS client encounters it, triggers a
referral. Similar to a symlink, a junction contains one or more target locations that the server sends
to clients in the form of an NFSv4 referral.

On Linux, an existing directory can be converted to a junction and back atomically and without the loss
of the directory contents. When a directory acts as a junction, it's local content is hidden from NFSv4
clients.

The nfsref(8) command is a simple way to get started managing junctions and their content.

Subcommands
Valid nfsref(8) subcommands are:

add Adds junction information to the directory named by pathname. The named directory must already
exist, and must not already contain junction information. Regular directory contents are obscured
to NFS clients by this operation.

A list of one or more file server and export path pairs is also specified on the command line.
When creating an NFS basic junction, this list is stored in an extended attribute of the
directory.

If junction creation is successful, the nfsref(8) command flushes the kernel's export cache to
remove previously cached junction information.

remove Removes junction information from the directory named by pathname. The named directory must
exist, and must contain junction information. Regular directory contents are made visible to NFS
clients again by this operation.

If junction deletion is successful, the nfsref(8) command flushes the kernel's export cache to
remove previously cached junction information.

lookup Displays junction information stored in the directory named by pathname. The named directory must
exist, and must contain junction information.

When looking up an NFS basic junction, the junction information in the directory is listed on
stdout.

Command line options
-d, --debug
Enables debugging messages during operation.

-t, --type=junction-type
Specifies the junction type for the operation. Valid values for junction-type are nfs-basic or
nfs-fedfs.

For the add subcommand, the default value if this option is not specified is nfs-basic. The nfs-
fedfs type is not used in this implementation.

For the remove and lookup subcommands, the --type option is not required. The nfsref(8) command
operates on whatever junction contents are available.

EXAMPLES

       Suppose you have two file servers, top.example.net and home.example.net.  You want all  your  clients  to
       mount top.example.net:/ and then see the files under home.example.net:/ automatically in top:/home.

       On top.example.net, you might issue this command as root:

              # mkdir /home
              # nfsref add /home home.example.net /
              Created junction /home.

AUTHOR