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EXPORTS(5)                  BSD 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.

     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 white-
     space.  The second is to specify the pathname of the root of the filesys-
     tem followed by the -alldirs flag; this form allows the host(s) to mount
     at any point within the filesystem, including regular files.  The path-
     names 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 filesys-
     tem 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 spec-
     ify 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 com-
     patible 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 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 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
     ``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 speci-
     fied 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_addr(3)).

     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=
           /u2 -maproot=root friends
           /u2 -alldirs -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 GID 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 associ-
     ated 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.

     /etc/exports  default remote mount-point file

     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 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.

     Regarding -alldirs, because NFS mount filehandles are filesystem wide the
     -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 /export and you wished to export the

           /export/root/client -alldirs client.foo.com

     you must realize that this also allows mounts to be requested against
     other locations in the /export filesystem; thus the host client.foo.com
     is also permitted to mount the directory /export/root/client2 if it

BSD                             March 30, 2017                             BSD