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           The  file  /etc/exports contains a table of local physical file systems
           on an NFS server that are accessible to NFS clients.  The  contents  of
           the file are maintained by the server's system administrator.
           Each file system in this table has a list of options and an access con-
           trol list.  The table is used by exportfs(8)  to  give  information  to
           The  file  format  is similar to the SunOS exports file. Each line con-
           tains an export  point  and  a  whitespace-separated  list  of  clients
           allowed  to mount the file system at that point. Each listed client may
           be immediately followed by a  parenthesized,  comma-separated  list  of
           export  options  for  that client. No whitespace is permitted between a
           client and its option list.
           Also, each line may have one or more specifications for default options
           after  the path name, in the form of a dash ("-") followed by an option
           list. The option list is used for all subsequent exports on  that  line
           Blank  lines  are  ignored.  A pound sign ("#") introduces a comment to
           the end of the line. Entries may be continued across newlines  using  a
           backslash.  If an export name contains spaces it should be quoted using
           double quotes. You can also specify spaces or other  unusual  character
           in  the export name using a backslash followed by the character code as
           three octal digits.
           To apply changes to this file,  run  exportfs-ra  or  restart  the  NFS
       Machine Name Formats
           NFS clients may be specified in a number of ways:
           single host
                  You  may specify a host either by an abbreviated name recognized
                  be the resolver,  the  fully  qualified  domain  name,  an  IPv4
                  address,  or  an IPv6 address. IPv6 addresses must not be inside
                  square brackets in /etc/exports lest they be confused with char-
                  acter-class wildcard matches.
           IP networks
                  You  can  also  export  directories to all hosts on an IP (sub-)
                  network simultaneously. This is done by specifying an IP address
                  and  netmask  pair  as  address/netmask where the netmask can be
                  specified in dotted-decimal format,  or  as  a  contiguous  mask
                  length.   For example, either '/' or '/22' appended
                  to the network base IPv4 address results  in  identical  subnet-
                  works with 10 bits of host. IPv6 addresses must use a contiguous
                  mask length and must not be inside square brackets to avoid con-
                  fusion  with character-class wildcards. Wildcard characters gen-
                  each netgroup members is consider in  checking  for  membership.
                  Empty  host  parts  or  those  containing  a single dash (-) are
                  This is specified by a single * character (not  to  be  confused
                  with the wildcard entry above) and will match all clients.
           If a client matches more than one of the specifications above, then the
           first match from the above list order takes precedence - regardless  of
           the  order they appear on the export line. However, if a client matches
           more than one of the same type of specification (e.g.  two  netgroups),
           then  the  first  match  from  the order they appear on the export line
           takes precedence.
       RPCSEC_GSS security
           You may use the special strings "gss/krb5", "gss/krb5i", or "gss/krb5p"
           to restrict access to clients using rpcsec_gss security.  However, this
           syntax is deprecated; on linux kernels since 2.6.23, you should instead
           use the "sec=" export option:
           sec=   The  sec= option, followed by a colon-delimited list of security
                  flavors, restricts the export to clients  using  those  flavors.
                  Available  security flavors include sys (the default--no crypto-
                  graphic security), krb5 (authentication only), krb5i  (integrity
                  protection),  and  krb5p (privacy protection).  For the purposes
                  of security flavor negotiation, order counts: preferred  flavors
                  should  be  listed  first.   The  order  of the sec= option with
                  respect to the other options does not matter,  unless  you  want
                  some options to be enforced differently depending on flavor.  In
                  that case you may include multiple sec= options,  and  following
                  options will be enforced only for access using flavors listed in
                  the immediately preceding sec= option.  The  only  options  that
                  are  permitted  to  vary in this way are ro, rw, no_root_squash,
                  root_squash, and all_squash.
       General Options
           exportfs understands the following export options:
           secure This option requires that requests originate on an Internet port
                  less  than IPPORT_RESERVED (1024). This option is on by default.
                  To turn it off, specify insecure.
           rw     Allow both read and write  requests  on  this  NFS  volume.  The
                  default is to disallow any request which changes the filesystem.
                  This can also be made explicit by using the ro option.
           async  This option allows the NFS server to violate  the  NFS  protocol
                  and  reply  to  requests before any changes made by that request
                  have been committed to stable storage (e.g. disc drive).
                  This option has no effect if async is also set.  The NFS  server
                  will  normally delay committing a write request to disc slightly
                  if it suspects that another related  write  request  may  be  in
                  progress  or  may  arrive  soon.   This  allows  multiple  write
                  requests to be committed to disc with the  one  operation  which
                  can improve performance.  If an NFS server received mainly small
                  unrelated requests, this behaviour could actually reduce perfor-
                  mance,  so  no_wdelay  is available to turn it off.  The default
                  can be explicitly requested with the wdelay option.
           nohide This option is based on the option of the same name provided  in
                  IRIX  NFS.  Normally, if a server exports two filesystems one of
                  which is mounted on the other, then  the  client  will  have  to
                  mount  both filesystems explicitly to get access to them.  If it
                  just mounts the parent, it will see an empty  directory  at  the
                  place where the other filesystem is mounted.  That filesystem is
                  Setting the nohide option on a filesystem causes it  not  to  be
                  hidden,  and  an appropriately authorised client will be able to
                  move from the parent to that  filesystem  without  noticing  the
                  However,  some  NFS clients do not cope well with this situation
                  as, for instance, it is then possible for two files in  the  one
                  apparent filesystem to have the same inode number.
                  The  nohide  option  is  currently only effective on single host
                  exports.  It does not work reliably with  netgroup,  subnet,  or
                  wildcard exports.
                  This option can be very useful in some situations, but it should
                  be used with due care, and only after confirming that the client
                  system copes with the situation effectively.
                  The option can be explicitly disabled with hide.
                  This  option  is  similar to nohide but it makes it possible for
                  clients to move from the  filesystem  marked  with  crossmnt  to
                  exported  filesystems mounted on it.  Thus when a child filesys-
                  tem "B" is mounted on a parent "A", setting crossmnt on "A"  has
                  the same effect as setting "nohide" on B.
                  This  option  disables subtree checking, which has mild security
                  implications, but can improve reliability in some circumstances.
                  If  a  subdirectory  of  a filesystem is exported, but the whole
                  filesystem isn't then whenever a NFS request arrives, the server
                  As  a  general guide, a home directory filesystem, which is nor-
                  mally exported at the root and may see  lots  of  file  renames,
                  should be exported with subtree checking disabled.  A filesystem
                  which is mostly readonly, and at least  doesn't  see  many  file
                  renames  (e.g. /usr or /var) and for which subdirectories may be
                  exported,  should  probably  be  exported  with  subtree  checks
                  The  default of having subtree checks enabled, can be explicitly
                  requested with subtree_check.
                  From release 1.1.0 of nfs-utils onwards,  the  default  will  be
                  no_subtree_check  as  subtree_checking tends to cause more prob-
                  lems than it is worth.  If you genuinely require subtree  check-
                  ing,  you should explicitly put that option in the exports file.
                  If you put neither option,  exportfs  will  warn  you  that  the
                  change is pending.
                  This  option (the two names are synonymous) tells the NFS server
                  not to require authentication of locking requests (i.e. requests
                  which  use  the  NLM  protocol).   Normally  the NFS server will
                  require a lock request to hold a credential for a user  who  has
                  read  access  to the file.  With this flag no access checks will
                  be performed.
                  Early NFS client implementations did not send  credentials  with
                  lock  requests,  and  many current NFS clients still exist which
                  are based on the old implementations.  Use this flag if you find
                  that you can only lock files which are world readable.
                  The  default  behaviour  of  requiring  authentication  for  NLM
                  requests can be explicitly requested with either of the  synony-
                  mous auth_nlm, or secure_locks.
           no_acl On  some  specially patched kernels, and when exporting filesys-
                  tems that support ACLs, this option tells  nfsd  not  to  reveal
                  ACLs  to  clients, so they will see only a subset of actual per-
                  missions on the given file system.   This  option  is  safe  for
                  filesystems  used  by  NFSv2  clients and old NFSv3 clients that
                  perform access decisions locally.  Current NFSv3 clients use the
                  ACCESS  RPC to perform all access decisions on the server.  Note
                  that the no_acl option only  has  effect  on  kernels  specially
                  patched  to  support it, and when exporting filesystems with ACL
                  support.  The default is to export with  ACL  support  (i.e.  by
                  default, no_acl is off).
                  NFS  needs  to  be  able  to  identify  each  filesystem that it
                  exports.  Normally it will use a UUID for the filesystem (if the
                  filesystem  has such a thing) or the device number of the device
                  holding the filesystem (if  the  filesystem  is  stored  on  the
                  As  not  all  filesystems  are  stored  on  devices, and not all
                  filesystems have UUIDs, it is sometimes necessary to  explicitly
                  tell  NFS  how  to identify a filesystem.  This is done with the
                  fsid= option.
                  For NFSv4, there is a distinguished filesystem which is the root
                  of all exported filesystem.  This is specified with fsid=root or
                  fsid=0 both of which mean exactly the same thing.
                  Other filesystems can be identified with a small integer,  or  a
                  UUID  which  should contain 32 hex digits and arbitrary punctua-
                  Linux kernels version 2.6.20 and earlier do not  understand  the
                  UUID  setting  so a small integer must be used if an fsid option
                  needs to be set for such kernels.  Setting both a  small  number
                  and a UUID is supported so the same configuration can be made to
                  work on old and new kernels alike.
                  A client referencing the export point will be directed to choose
                  from  the given list an alternative location for the filesystem.
                  (Note that the server must have a mountpoint here, though a dif-
                  ferent filesystem is not required; so, for example, mount --bind
                  /path /path is sufficient.)
                  If the client asks for  alternative  locations  for  the  export
                  point,  it  will  be given this list of alternatives. (Note that
                  actual replication of the filesystem must be handled elsewhere.)
       User ID Mapping
           nfsd bases its access control to files on the server machine on the uid
           and gid provided in each NFS RPC request. The normal  behavior  a  user
           would expect is that she can access her files on the server just as she
           would on a normal file system. This requires that  the  same  uids  and
           gids  are used on the client and the server machine. This is not always
           true, nor is it always desirable.
           Very often, it is not desirable that the root user on a client  machine
           is also treated as root when accessing files on the NFS server. To this
                  equally sensitive, such as user bin or group staff.
                  Turn  off root squashing. This option is mainly useful for disk-
                  less clients.
                  Map all uids and gids to the anonymous  user.  Useful  for  NFS-
                  exported  public  FTP  directories, news spool directories, etc.
                  The opposite option is no_all_squash, which is the default  set-
           anonuid and anongid
                  These  options  explicitly  set the uid and gid of the anonymous
                  account.  This option is primarily useful  for  PC/NFS  clients,
                  where you might want all requests appear to be from one user. As
                  an example, consider the export entry for /home/joe in the exam-
                  ple  section below, which maps all requests to uid 150 (which is
                  supposedly that of user joe).
       Extra Export Tables
           After reading /etc/exports exportfs reads files  under  /etc/exports.d.
           directory  as  extra export tables.  exportfs regards only a file which
           name is ended with .exports and not started with .  as an extra  export
           file. A file which name is not met this condition is just ignored.  The
           format for extra export tables is the same as /etc/exports


           # sample /etc/exports file
           /               master(rw) trusty(rw,no_root_squash)
           /projects       proj*.local.domain(rw)
           /usr            *.local.domain(ro) @trusted(rw)
           /home/joe       pc001(rw,all_squash,anonuid=150,anongid=100)
           /pub            *(ro,insecure,all_squash)
           /srv/www        -sync,rw server @trusted @external(ro)
           /foo            2001:db8:9:e54::/64(rw)
           /build          buildhost[0-9].local.domain(rw)
           The first line exports the entire filesystem  to  machines  master  and
           trusty.   In  addition to write access, all uid squashing is turned off
           for host trusty. The second and third entry show examples for  wildcard
           hostnames and netgroups (this is the entry '@trusted'). The fourth line
           shows the entry for the PC/NFS client discussed above. Line  5  exports
           the  public  FTP  directory  to  every host in the world, executing all
           requests under the nobody account. The insecure option  in  this  entry
           also  allows clients with NFS implementations that don't use a reserved
           port for NFS.  The sixth line exports a  directory  read-write  to  the
           machine  'server'  as well as the '@trusted' netgroup, and read-only to
           netgroup '@external', all three mounts with the 'sync' option  enabled.
           The  seventh  line exports a directory to both an IPv6 and an IPv4 sub-
           net. The eighth line demonstrates a character class wildcard match.

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