define remote mount points for NFS mount
file specifies remote mount
points for the NFS mount protocol per the NFS server specification; see
Network File System Protocol Specification,
Appendix A and NFS: Network File System Version 3
RFC 1813, Appendix I.
Each line in the file (other than comment lines that begin with a
“#”) specifies the mount point(s) and export flags within one
local server filesystem for one or more hosts. A host may be specified only
once for each local filesystem on the server and there may be only one default
entry for each server filesystem that applies to all other hosts. The latter
exports the filesystem to the “world” and should be used only
when the filesystem contains public information.
In a mount entry, the first field(s) specify the directory path(s) within a
server filesystem that can be mounted on by the corresponding client(s). There
are two forms of this specification. The first is to list all mount points as
absolute directory paths separated by whitespace. The second is to specify the
pathname of the root of the filesystem followed by the
flag; this form allows the host(s)
to mount at any point within the filesystem, including regular files. The
pathnames must not have any symbolic links in them and should not have any
“.” or “..” components. Mount points for a
filesystem may appear on multiple lines each with different sets of hosts and
The second component of a line specifies how the filesystem is to be exported to
the host set. The option flags specify whether the filesystem is exported
read-only or read-write and how the client UID is mapped to user credentials
on the server.
Export options are specified as follows:
The credential of the specified user is used for remote access by root. The
credential includes all the groups to which the user is a member on the local
machine (see id(1)
may be specified by name or number.
The colon separated list is used to specify the precise credential to be used
for remote access by root. The elements of the list may be either names or
numbers. Note that user: should be used to distinguish a credential containing
no groups from a complete credential for that user.
Specifies a mapping for all client UIDs (including root) using the same
is a synonym for
in an effort to be backward
compatible with older export file formats.
In the absence of
options, remote accesses by root
will result in using a credential of -2:-2. All other users will be mapped to
their remote credential. If a
option is given, remote access by root will be mapped to that credential
instead of -2:-2. If a
given, all users (including root) will be mapped to that credential in place
of their own.
option specifies that the filesystem
should be exported read-only (default read/write). The option
is a synonym for
in an effort to be backward compatible
with older export file formats.
The third component of a line specifies the host set to which the line applies.
The set may be specified in three ways. The first way is to list the host
name(s) separated by whitespace. (Standard internet “dot”
addresses may be used in place of names.) The second way is to specify a
“netgroup” as defined in the netgroup file (see
). The third way is
to specify an internet subnetwork using a network and network mask that is
defined as the set of all hosts with addresses within the subnetwork. This
latter approach requires less overhead within the kernel and is recommended
for cases where the export line refers to a large number of clients within an
The first two cases are specified by simply listing the name(s) separated by
whitespace. All names are checked to see if they are “netgroup”
names first and are assumed to be hostnames otherwise. Using the full domain
specification for a hostname can normally circumvent the problem of a host
that has the same name as a netgroup. The third case is specified by the flag
. If the mask is not specified, it
will default to the mask for that network class (A, B or C; see
/usr /usr/local -maproot=0:10 friends
/usr -maproot=daemon grumpy.cis.uoguelph.ca 126.96.36.199
/usr -ro -mapall=nobody
/u -maproot=bin: -network=131.104.48 -mask=255.255.255.0
/u2 -maproot=root friends
/u2 -alldirs -network=cis-net -mask=cis-mask
Given that /usr
are local filesystem mount points, the
above example specifies the following: /usr
is exported to hosts friends
is specified in the netgroup file with
users mapped to their remote credentials and root mapped to UID 0 and GID 10.
It is exported read-write and the hosts in “friends” can mount
. It is exported to
with users mapped to their
remote credentials and root mapped to the user and groups associated with
“daemon”; it is exported to the rest of the world as read-only
with all users mapped to the user and groups associated with
is exported to all hosts on the subnetwork
with root mapped to the UID for
“bin” and with no group access.
is exported to the hosts in
“friends” with root mapped to UID and groups associated with
“root”; it is exported to all hosts on network
“cis-net” allowing mounts at any directory within /u2.
- default remote mount-point file
The export options are tied to the local mount points in the kernel and must be
non-contradictory for any exported subdirectory of the local server mount
point. It is recommended that all exported directories within the same server
filesystem be specified on adjacent lines going down the tree. You cannot
specify a hostname that is also the name of a netgroup. Specifying the full
domain specification for a hostname can normally circumvent the problem.
, because NFS mount
filehandles are filesystem wide the
option applies to exports of the
entire filesystem — even mountpoints that are higher up elsewhere in
the directory hierarchy. Hence if the server has a filesystem
and you wished to export the
/export/root/client -alldirs client.foo.com
you must realize that this also allows mounts to be requested against other
locations in the /export
the host client.foo.com is also permitted to mount the directory
if it exists.