NetBSD-5.0.2/usr.sbin/mountd/exports.5

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.\"     @(#)exports.5	8.3 (Berkeley) 3/29/95
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.Dd October 8, 2006
.Dt EXPORTS 5
.Os
.Sh NAME
.Nm exports
.Nd define remote mount points for
.Tn NFS
mount requests
.Sh SYNOPSIS
.Nm exports
.Sh DESCRIPTION
The
.Nm exports
file specifies remote mount points for the
.Tn NFS
mount protocol per the
.Tn NFS
server specification; see
.%T "Network File System Protocol Specification \\*(tNRFC\\*(sP 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
.Sq # )
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
If you have modified the
.Pa /etc/exports
file, send the mountd a SIGHUP to make it re-read the
.Pa /etc/exports
file:
.Dq kill -HUP `cat /var/run/mountd.pid` .
.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.
Note that the
.Fl alldirs
option should not be used as a security measure to make clients mount
only those subdirectories that they should have access to.
A client
can still access the whole filesystem via individual RPCs if it
wanted to, even if just one subdirectory has been mounted.
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 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 kerb
option specifies that the Kerberos authentication server should be
used to authenticate and map client credentials.
This option is currently not implemented.
.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
.Fl noresvport
option specifies that NFS RPC calls for the filesystem do not have to come
from reserved ports.
Normally, clients are required to use reserved ports for operations.
Using this option decreases the security of your system.
.Pp
The
.Fl noresvmnt
option specifies that mount RPC requests for the filesystem do not have
to come from reserved ports.
Normally, clients are required to use reserved ports for mount requests.
Using this option decreases the security of your system.
.Pp
WebNFS exports strictly according to the spec (RFC 2054 and RFC 2055) can
be done with the
.Fl public
flag.
However, this flag in itself allows r/w access to all files in
the filesystem, not requiring reserved ports and not remapping uids.
It is only provided to conform to the spec, and should normally
not be used.
For a WebNFS export,
use the
.Fl webnfs
flag, which implies
.Fl public ,
.Sm off
.Fl mapall No = Ar nobody
.Sm on
and
.Fl ro .
.Pp
A
.Sm off
.Fl index No = Ar file
.Sm on
option can be used to specify a file whose handle will be returned if
a directory is looked up using the public filehandle (WebNFS).
This is to mimic the behavior of URLs.
If no
.Fl index
option is specified, a directory filehandle will be returned as usual.
The
.Fl index
option only makes sense in combination with the
.Fl public
or
.Fl webnfs
flags.
.Pp
.Bf -symbolic
Warning: exporting a filesystem both using WebNFS and read/write in
the normal way to other hosts should be avoided in an environment
that is vulnerable to IP spoofing.
.Ef
WebNFS enables any client to get filehandles to the exported filesystem.
Using IP spoofing, a client could then pretend to be a host to which
the same filesystem was exported read/write, and use the handle to
gain access to that filesystem.
.Pp
The third component of a line specifies the host set to which the line applies.
If no host set is specified, the filesystem is exported to everyone.
The set may be specified in three ways.
The first way is to list the host name(s) separated by white space.
(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 ) .
A netgroup that contains an item that does have a host entry
is treated like an error.
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 Op No / Ar prefixlength
.Sm on
and optionally
.Sm off
.Fl mask No = Ar netmask .
.Sm on
The netmask may be specified either by attaching a
.Ar prefixlength
to the
.Fl network
option, or by using a separate
.Fl mask
option.
If the mask is not specified, it will default to the mask for that network
class (A, B or C; see
.Xr inet 4 ) .
.Pp
Scoped IPv6 address must carry scope identifier as documented in
.Xr inet6 4 .
For example,
.Dq fe80::%ne2/10
is used to specify fe80::/10 on ne2 interface.
.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
/a -network 192.168.0/24
/a -network 3ffe:1ce1:1:fe80::/64
/u2 -maproot=root friends
/u2 -alldirs -kerb -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 friends is specified in the netgroup file
with users mapped to their remote credentials and
root mapped to uid 0 and group 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 and mapping all uids to credentials for the principal
that is authenticated by a Kerberos ticket.
.Pp
.Pa /a
is exported to the network 192.168.0.0, with a netmask of 255.255.255.0.
However, the netmask length in the entry for /a is not specified through
a -mask option, but through the /prefix notation.
.Pp
.Pa /a
is also exported to the IPv6 network 3ffe:1ce1:1:fe80:: address, using
the upper 64 bits as the prefix.
Note that, unlike with IPv4 network addresses, the specified network
address must be complete, and not just contain the upper bits.
With IPv6 addresses, the -mask option must not
be used.
.Sh FILES
.Bl -tag -width /etc/exports -compact
.It Pa /etc/exports
The default remote mount-point file.
.El
.Sh SEE ALSO
.Xr netgroup 5 ,
.Xr mountd 8 ,
.Xr nfsd 8 ,
.Xr showmount 8
.Sh CAVEATS
Don't re-export NFS-mounted filesystems unless you are sure of the
implications.
NFS has some assumptions about the characteristics of the file
systems being exported, e.g. when timestamps are updated.
Re-exporting should work to some extent and can even be useful in
some cases, but don't expect it works as well as with local file
systems.
.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.