exports.5

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.\"     @(#)exports.5	8.3 (Berkeley) 3/29/95
.\" $FreeBSD: src/sbin/mountd/exports.5,v 1.10.2.8 2002/09/28 16:31:45 markm Exp $
.\"
.Dd March 14, 2018
.Dt EXPORTS 5
.Os
.Sh NAME
.Nm exports
.Nd define remote mount points for
.Tn NFS
mount requests
.Sh SYNOPSIS
.Nm
.Sh DESCRIPTION
The
.Nm
file specifies remote mount points for the
.Tn NFS
mount protocol per the
.Tn 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 #)
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.
This list of directory paths should be considered an
.Dq administrative control ,
since it is only enforced by the
.Xr mountd 8
daemon and not the kernel.
As such, it only applies to NFSv2 and NFSv3 mounts and only
with respect to the client's use of the mount protocol.
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 if the
.Fl r
option is used on
.Xr mountd 8 .
The pathnames must not have any symbolic links in them and should not have
any
.Dq Pa \&.
or
.Dq Pa ..
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 Li = Sy 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 Li = Sy 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 Li = Sy user
.Sm on
or
.Sm off
.Fl mapall Li = Sy 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 65534:65533.
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 65534:65533.
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
.Tn 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 file system, 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
.Tn WebNFS
export,
use the
.Fl webnfs
flag, which implies
.Fl public ,
.Sm off
.Fl mapall No = Sy nobody
.Sm on
and
.Fl ro .
.Pp
A
.Sm off
.Fl index No = Sy 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
.Pq Tn 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
Specifying the
.Fl quiet
option will inhibit some of the syslog diagnostics for bad lines in
.Pa /etc/exports .
This can be useful to avoid annoying error messages for known possible
problems (see
.Sx EXAMPLES
below).
.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 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
.Pa 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 Li = Sy netname Op Li / Ar prefixlength
.Sm on
and optionally
.Sm off
.Fl mask No = Sy 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 ) .
See the
.Sx EXAMPLES
section below.
.Pp
The
.Xr mountd 8
utility can be made to re-read the
.Nm
file by sending it a hangup signal as follows:
.Bd -literal -offset indent
/etc/rc.d/mountd reload
.Ed
.Pp
After sending the
.Dv SIGHUP ,
check the
.Xr syslogd 8
output to see whether
.Xr mountd 8
logged any parsing errors in the
.Nm
file.
.Sh FILES
.Bl -tag -width /etc/exports -compact
.It Pa /etc/exports
the default remote mount-point file
.El
.Sh EXAMPLES
.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
/u2 -maproot=root friends
/u2 -alldirs -network cis-net -mask cis-mask
/cdrom -alldirs,quiet,ro -network 192.168.33.0 -mask 255.255.255.0
.Ed
.Pp
Given that
.Pa /usr ,
.Pa /u ,
.Pa /a
and
.Pa /u2
are
local filesystem mount points, the above example specifies the following:
.Pp
The file system rooted at
.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
The file system rooted at
.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
The file system rooted at
.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.
.Pp
The file system rooted at
.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
.Pa /a
is not specified through a
.Fl mask
option, but through the
.Li / Ns Ar prefix
notation.
.Pp
The filesystem rooted at
.Pa /cdrom
will exported read-only to the entire network 192.168.33.0/24, including
all its subdirectories.
Since
.Pa /cdrom
is the conventional mountpoint for a CD-ROM device, this export will
fail if no CD-ROM medium is currently mounted there since that line
would then attempt to export a subdirectory of the root filesystem
with the
.Fl alldirs
option which is not allowed.
The
.Fl quiet
option will then suppress the error message for this condition that
would normally be syslogged.
As soon as an actual CD-ROM is going to be mounted,
.Xr mount 8
will notify
.Xr mountd 8
about this situation, and the
.Pa /cdrom
filesystem will be exported as intended.
Note that without using the
.Fl alldirs
option, the export would always succeed.
While there is no CD-ROM medium mounted under
.Pa /cdrom ,
it would export the (normally empty) directory
.Pa /cdrom
of the root filesystem instead.
.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.