exports -- define remote mount points for NFS mount requests
The exports file specifies remote mount points for the NFS mount protocol
per the NFS server specification; see Network File System Protocol
Specification, RFC1094, Appendix A and NFS: Network File System Version 3
Specification, 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
file system for one or more hosts. A long line may be split over several
lines by ending all but the last line with a backslash (`\'). A host may
be specified only once for each local file system on the server and there
may be only one default entry for each server file system that applies to
all other hosts. The latter exports the file system to the ``world'' and
should be used only when the file system contains public information.
In a mount entry, the first field(s) specify the directory path(s) within
a server file system 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 file
system followed by the -alldirs flag; this form allows the host(s) to
mount at any point within the file system, including regular files if the
-r option is used on mountd(8). The pathnames must not have any symbolic
links in them and should not have any "." or ".." components. Mount
points for a file system may appear on multiple lines each with different
sets of hosts and export options.
The second component of a line specifies how the file system is to be
exported to the host set. The option flags specify whether the file system
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:
-maproot=user 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)). The user may be specified
by name or number.
-maproot=user:group1:group2:... 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.
-mapall=user or -mapall=user:group1:group2:... specifies a mapping for
all client uids (including root) using the same semantics as -maproot.
The option -r is a synonym for -maproot in an effort to be backward compatible
with older export file formats.
In the absence of -maproot and -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 -maproot option is given, remote
access by root will be mapped to that credential instead of -2:-2. If a
-mapall option is given, all users (including root) will be mapped to
that credential in place of their own.
The -ro option specifies that the file system should be exported readonly
(default read/write). The option -o is a synonym for -ro in an
effort to be backward compatible with older export file formats.
WebNFS exports strictly according to the spec (RFC 2054 and RFC 2055) can
be done with the -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 WebNFS export, use the -webnfs flag,
which implies -public, -mapall=nobody and -ro.
A -index=file 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 -index option is
specified, a directory filehandle will be returned as usual. The -index
option only makes sense in combination with the -public or -webnfs flags.
Specifying the -quiet option will inhibit some of the syslog diagnostics
for bad lines in /etc/exports. This can be useful to avoid annoying
error messages for known possible problems (see EXAMPLES below).
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
``dot'' addresses may be used in place of names.) The second way is to
specify a ``netgroup'' as defined in the netgroup file (see 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.
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 -network=netname and optionally -mask=netmask. If the
mask is not specified, it will default to the mask for that network class
(A, B or C; see inet(4)). See the EXAMPLES section below.
The mountd(8) utility can be made to re-read the exports file by sending
it a hangup signal as follows:
kill -s HUP `cat /var/run/mountd.pid`
After sending the SIGHUP, check the syslogd(8) output to see whether
mountd(8) logged any parsing errors in the exports file.
/etc/exports the default remote mount-point file
/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
/cdrom -alldirs,quiet,ro -network 192.168.33.0 -mask 255.255.255.0
Given that /usr, /u and /u2 are local file system mount points, the above
example specifies the following: /usr is exported to hosts 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 ``friends'' can mount either /usr or
/usr/local. It is exported to 188.8.131.52 and grumpy.cis.uoguelph.ca
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
/u is exported to all hosts on the subnetwork 131.104.48 with root mapped
to the uid for ``bin'' and with no group access.
/u2 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.
The file system rooted at /cdrom will exported read-only to the entire
network 192.168.33.0/24, including all its subdirectories. Since /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 file system with the
-alldirs option which is not allowed. The -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, mount(8)
will notify mountd(8) about this situation, and the /cdrom file system
will be exported as intended. Note that without using the -alldirs
option, the export would always succeed. While there is no CD-ROM medium
mounted under /cdrom, it would export the (normally empty) directory
/cdrom of the root file system instead.
netgroup(5), mountd(8), nfsd(8), showmount(8)
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 file system 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.
FreeBSD 5.2.1 March 29, 1995 FreeBSD 5.2.1 [ Back ]