utils/nfsref/nfsref.man

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.\" @file utils/nfsref/nfsref.man
.\" @brief man page for nfsref command
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.TH NFSREF 8 "9 Jan 2018"
.SH NAME
nfsref \- manage NFS referrals
.SH SYNOPSIS
.B nfsref
.RB [ \-?d ]
.RB [ \-t
.IB type ]
.B add
.I pathname server export
.RI [ " server"
.IR export " ... ]"
.P
.B nfsref
.RB [ \-?d ]
.RB [ \-t
.IB type ]
.B remove
.I pathname
.P
.B nfsref
.RB [ \-?d ]
.RB [ \-t
.IB type ]
.B lookup
.I pathname
.SH INTRODUCTION
NFS version 4 introduces the concept of
.I file system referrals
to NFS.
A file system referral is like a symbolic link on a file server
to another file system share, possibly on another file server.
On an NFS client, a referral behaves like an automounted directory.
The client, under the server's direction, mounts a new NFS export
automatically when an application first accesses that directory.
.P
Referrals are typically used to construct a single file name space
across multiple file servers.
Because file servers control the shape of the name space,
no client configuration is required,
and all clients see the same referral information.
.P
The Linux NFS server supports NFS version 4 referrals.
Administrators can specify the
.B refer=
export option in
.I /etc/exports
to configure a list of exports from which the client can choose.
See
.BR exports (5)
for details.
.P
.SH DESCRIPTION
The
.BR nfsref (8)
command is a simple way to get started managing junction metadata.
Other administrative commands provide richer access to junction information.
.SS Subcommands
Valid
.BR nfsref (8)
subcommands are:
.IP "\fBadd\fP"
Adds junction information to the directory named by
.IR 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.
.IP
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.
.IP
If junction creation is successful, the
.BR nfsref (8)
command flushes the kernel's export cache
to remove previously cached junction information.
.IP "\fBremove\fP"
Removes junction information from the directory named by
.IR pathname .
The named directory must exist,
and must contain junction information.
Regular directory contents are made visible to NFS clients again by this operation.
.IP
If junction deletion is successful, the
.BR nfsref (8)
command flushes the kernel's export cache
to remove previously cached junction information.
.IP "\fBlookup\fP"
Displays junction information stored in the directory named by
.IR pathname .
The named directory must exist,
and must contain junction information.
.IP
When looking up an NFS basic junction, the junction information
in the directory is listed on
.IR stdout .
.SS Command line options
.IP "\fB\-d, \-\-debug"
Enables debugging messages during operation.
.IP "\fB\-t, \-\-type=\fIjunction-type\fP"
Specifies the junction type for the operation.  Valid values for
.I junction-type
are
.B nfs-basic
or
.BR nfs-fedfs .
.IP
For the
.B add
subcommand, the default value if this option is not specified is
.BR nfs-basic .
For the
.B remove
and
.B lookup
subcommands, the
.B \-\-type
option is not required.  The
.BR nfsref (8)
command operates on whatever junction contents are available.
.SH EXAMPLES
Suppose you have two file servers,
.I top.example.net
and
.IR home.example.net .
You want all your clients to mount
.I top.example.net:/
and then see the files under
.I home.example.net:/
automatically in
.IR top:/home .
.P
On
.IR top.example.net ,
you might issue this command as root:
.RS
.sp
# mkdir /home
.br
# nfsref --type=nfs-basic add /home home.example.net /
.br
Created junction /home.
.sp
.RE
.SH FILES
.TP
.I /etc/exports
NFS server export table
.SH "SEE ALSO"
.BR exports (5)
.sp
RFC 5661 for a description of NFS version 4 referrals
.SH "AUTHOR"
Chuck Lever <chuck.lever@oracle.com>