path: root/sbin/mountd/exports.5

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.\"     @(#)exports.5	8.3 (Berkeley) 3/29/95
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.Dd $Mdocdate: May 9 2014 $
.Dt EXPORTS 5
.Os
.Sh NAME
.Nm exports
.Nd define remote mount points for NFS mount requests
.Sh SYNOPSIS
.Nm exports
.Sh DESCRIPTION
The
.Nm
file specifies remote mount points for the NFS
mount protocol per the NFS server specification; see
.%T "Network File System Protocol Specification RFC 1094, Appendix A"
and
.%T "NFS: Network File System Version 3 Specification, Appendix I" .
.Pp
Each line in the file
(other than comment lines that begin with a
.Dq # )
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
.Dq world
and should
be used only when the filesystem contains public information.
.Pp
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
.Fl alldirs
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
.Dq \&.
or
.Dq \&.\&.
components.
Mount points for a filesystem may appear on multiple lines each with
different sets of hosts and export options.
.Pp
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.
.Pp
Export options are specified as follows:
.Pp
.Sm off
.Fl maproot No = Ar user
.Sm on
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
.Xr id 1 ) .
The
.Ar user
may be specified by name or number.
.Pp
.Sm off
.Fl maproot No = Ar user:group1:group2:...
.Sm on
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.
.Pp
.Sm off
.Fl mapall No = Ar user
.Sm on
or
.Sm off
.Fl mapall No = Ar user:group1:group2:...
.Sm on
Specifies a mapping for all client UIDs (including root)
using the same semantics as
.Fl maproot .
.Pp
The option
.Fl r
is a synonym for
.Fl maproot
in an effort to be backward compatible with older export file formats.
.Pp
In the absence of
.Fl maproot
and
.Fl mapall
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
.Fl maproot
option is given,
remote access by root will be mapped to that credential instead of -2:-2.
If a
.Fl mapall
option is given,
all users (including root) will be mapped to that credential in
place of their own.
.Pp
The
.Fl ro
option specifies that the filesystem should be exported read-only
(default read/write).
The option
.Fl o
is a synonym for
.Fl ro
in an effort to be backward compatible with older export file formats.
.Pp
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
.Dq dot
addresses may be used in place of names.)
The second way is to specify a
.Dq netgroup
as defined in the netgroup file (see
.Xr netgroup 5 ) .
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 administrative subnet.
.Pp
The first two cases are specified by simply listing the name(s) separated
by whitespace.
All names are checked to see if they are
.Dq 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
.Sm off
.Fl network No = Ar netname
.Sm on
and optionally
.Sm off
.Fl mask No = Ar netmask .
.Sm on
If the mask is not specified, it will default to the mask for that network
class (A, B or C; see
.Xr inet_addr 3 ) .
.Pp
For example:
.Bd -literal -offset indent
/usr /usr/local -maproot=0:10 friends
/usr -maproot=daemon grumpy.cis.uoguelph.ca 131.104.48.16
/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
.Ed
.Pp
Given that
.Pa /usr ,
.Pa /u
and
.Pa /u2
are
local filesystem mount points, the above example specifies the following:
.Pa /usr
is exported to hosts
.Em friends
where
.Em 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
.Dq friends
can mount either
.Pa /usr
or
.Pa /usr/local .
It is exported to
.Em 131.104.48.16
and
.Em grumpy.cis.uoguelph.ca
with users mapped to their remote credentials and
root mapped to the user and groups associated with
.Dq daemon ;
it is exported to the rest of the world as read-only with
all users mapped to the user and groups associated with
.Dq nobody .
.Pp
.Pa /u
is exported to all hosts on the subnetwork
.Em 131.104.48
with root mapped to the UID for
.Dq bin
and with no group access.
.Pp
.Pa /u2
is exported to the hosts in
.Dq friends
with root mapped to UID and groups
associated with
.Dq root ;
it is exported to all hosts on network
.Dq cis-net
allowing mounts at any
directory within /u2.
.Sh FILES
.Bl -tag -width /etc/exports -compact
.It Pa /etc/exports
default remote mount-point file
.El
.Sh SEE ALSO
.Xr netgroup 5 ,
.Xr mountd 8 ,
.Xr nfsd 8 ,
.Xr showmount 8
.Sh BUGS
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.
.Pp
Regarding
.Fl alldirs ,
because NFS mount filehandles are filesystem wide the
.Fl alldirs
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
.Pa /export
and you wished to export the sub-directory
.Bd -literal -offset indent
/export/root/client -alldirs client.foo.com
.Ed
.Pp
you must realize that this also allows mounts to be requested
against other locations in the
.Pa /export
filesystem; thus the host client.foo.com is also permitted to
mount the directory
.Pa /export/root/client2
if it exists.