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EXPORTS(5)                    File Formats Manual                   EXPORTS(5)

     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 RFC 1094, 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
     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.

     If you have modified the /etc/exports file, send the mountd a SIGHUP to
     make it re-read the /etc/exports file: "kill -HUP `cat

     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 -alldirs flag; this form allows the host(s) to
     mount at any point within the filesystem, including regular files.  Note
     that the -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 "." or
     ".." components.  Mount points for a filesystem may appear on multiple
     lines each with different sets of hosts and export options.

     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:

     -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 -kerb option specifies that the Kerberos authentication server should
     be used to authenticate and map client credentials.  This option is
     currently not implemented.

     The -ro option specifies that the filesystem should be exported read-only
     (default read/write).  The option -o is a synonym for -ro in an effort to
     be backward compatible with older export file formats.

     The -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.

     The -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.

     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 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 -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.

     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.  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.

     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 "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)).  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.

     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[/prefixlength] and optionally -mask=netmask.
     The netmask may be specified either by attaching a prefixlength to the
     -network option, or by using a separate -mask option.  If the mask is not
     specified, it will default to the mask for that network class (A, B or C;
     see inet(4)).

     Scoped IPv6 address must carry scope identifier as documented in
     inet6(4).  For example, "fe80::%ne2/10" is used to specify fe80::/10 on
     ne2 interface.

     For example:

           /usr /usr/local -maproot=0:10 friends
           /usr -maproot=daemon grumpy.cis.uoguelph.ca
           /usr -ro -mapall=nobody
           /u -maproot=bin: -network 131.104.48 -mask
           /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

     Given that /usr, /u, and /u2 are local filesystem 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 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 with "nobody".

     /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 and mapping all
     uids to credentials for the principal that is authenticated by a Kerberos

     /a is exported to the network, with a netmask of  However, the netmask length in the entry for /a is not
     specified through a -mask option, but through the /prefix notation.

     /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.

     /etc/exports  The default remote mount-point file.

     netgroup(5), mountd(8), nfsd(8), showmount(8)

     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.

     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.

NetBSD 10.99                    October 8, 2006                   NetBSD 10.99