exportfs



exportfs(8)                                                        exportfs(8)




NAME

       exportfs - maintain list of NFS exported file systems


SYNOPSIS

       /usr/sbin/exportfs [-avi] [-o options,..] [client:/path ..]
       /usr/sbin/exportfs -r [-v]
       /usr/sbin/exportfs [-av] -u [client:/path ..]
       /usr/sbin/exportfs [-v]
       /usr/sbin/exportfs -f


DESCRIPTION

       The  exportfs command is used to maintain the current table of exported
       file systems for NFS. This list  is  kept  in  a  separate  file  named
       /var/lib/nfs/xtab  which  is read by mountd when a remote host requests
       access to mount a file tree, and parts of the list which are active are
       kept in the kernel’s export table.

       Normally  this  xtab file is initialized with the list of all file sys-
       tems named in /etc/exports by invoking exportfs -a.

       However, administrators can choose to add and  delete  individual  file
       systems without modifying /etc/exports using exportfs.

       exportfs  and  it’s  partner program mountd work in one of two modes, a
       legacy mode which applies to 2.4 and earlier versions of the Linux ker-
       nel,  and  a new mode which applies to 2.6 and later versions providing
       the nfsd virtual  filesystem  has  been  mounted  at  /proc/fs/nfsd  or
       /proc/fs/nfs.   If  this  filesystem  is not mounted in 2.6, the legacy
       mode is used.

       In the new mode, exportfs does not give any information to  the  kernel
       but  only  provides  it  to  mountd through the /var/lib/nfs/xtab file.
       mountd will listen to requests from the kernel and will provide  infor-
       mation as needed.

       In  the legacy mode, any export requests which identify a specific host
       (rather than a subnet or netgroup etc) are entered  directly  into  the
       kernel’s  export  table  as well as being written to /var/lib/nfs/xtab.
       Further, any mount points listed in /var/lib/nfs/rmtab  which  match  a
       non host-specific export request will cause an appropriate export entry
       for the host given in rmtab to be entered into the kernel’s export  ta-
       ble.


OPTIONS

       -a     Export or unexport all directories.

       -o options,...
              Specify  a  list  of  export  options  in  the same manner as in
              exports(5).

       -i     Ignore the /etc/exports file, so that only default  options  and
              options given on the command line are used.

       -r     Reexport all directories. It synchronizes /var/lib/nfs/xtab with
              /etc/exports. It removes entries in /var/lib/nfs/xtab which  are
              deleted  from /etc/exports, and remove any entries from the ker-
              nel export table which are no longer valid.

       -u     Unexport one or more directories.

       -f     In ’new’ mode, flush everything out of the kernels export table.
              Any clients that are active will get new entries added by mountd
              when they make their next request.

       -v     Be verbose. When exporting or unexporting, show what’s going on.
              When  displaying  the current export list, also display the list
              of export options.


DISCUSSION

   Exporting Directories
       The first synopsis shows how to invoke  the  command  when  adding  new
       entries  to  the export table.  When using exportfs -a, all directories
       in exports(5) are added to xtab and the resulting list is  pushed  into
       the kernel.

       The  host:/path  argument  specifies the directory to export along with
       the host or hosts to export it to. All formats described in  exports(5)
       are  supported;  to  export  a  directory  to the world, simply specify
       :/path.

       The export options for a particular  host/directory  pair  derive  from
       several  sources.  There is a set of default options which can be over-
       ridden by entries in /etc/exports (unless the -i option is given).   In
       addition,  the administrator may overide any options from these sources
       using the -o argument which takes a comma-separated list of options  in
       the  same  fashion  as  one  would  specify  them in exports(5).  Thus,
       exportfs can also be used to modify the export options  of  an  already
       exported directory.

       Modifications  of  the  kernel  export table used by nfsd(8) take place
       immediately after parsing the command line and updating the xtab  file.

       The default export options are sync,ro,root_squash,no_delay.

   Unexporting Directories
       The  third synopsis shows how to unexported a currently exported direc-
       tory.  When using exportfs -ua, all entries listed in xtab are  removed
       from  the  kernel  export  tables, and the file is cleared. This effec-
       tively shuts down all NFS activity.

       To remove individial export entries, one can specify a host:/path pair.
       This  deletes the specified entry from xtab and removes the correspond-
       ing kernel entry (if any).


   Dumping the Export Table
       Invoking exportfs without further options shows  the  current  list  of
       exported  file  systems.   When giving the -v option, the list of flags
       pertaining to each export are shown in addition.


EXAMPLES

       The  following  adds  all  directories  listed   in   /etc/exports   to
       /var/lib/nfs/xtab and pushes the resulting export entries into the ker-
       nel:

       # exportfs -a

       To export the /usr/tmp directory to host djando, allowing  asynchronous
       writes, one would do this:

       # exportfs -o async django:/usr/tmp


DEPENDENCIES

       Exporting  to  IP networks, DNS and NIS domains does not enable clients
       from these groups to access NFS immediately;  rather,  these  sorts  of
       exports  are  hints to mountd(8) to grant any mount requests from these
       clients.  This is usually not  a  big  problem,  because  any  existing
       mounts are preserved in rmtab across reboots.

       When unexporting a network or domain entry, any current exports to mem-
       bers of this group will be checked against the remaining valid  exports
       and if they themselves are nolonger valid they will be removed.



SEE ALSO

       exports(5), mountd(8)


AUTHORS

       Olaf Kirch, <okir@monad.swb.de>
       Neil Brown, <neilb@cse.unsw.edu.au>




                                 18 July 2003                      exportfs(8)

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