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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, 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 or the	NFSv4 tree root	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
     or	the NFSv4 tree root 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 three forms of this specification.  The first is to
     list all mount points as absolute directory paths separated by white-
     space.  This list of directory paths should be considered an
     "administrative control", since it	is only	enforced by the	mountd(8) dae-
     mon and not the kernel.  As such, it only applies to NFSv2	and NFSv3
     mounts and	only with respect to the client's use of the mount protocol.
     The second	is to specify the pathname of the root of the file system fol-
     lowed 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).	 Because NFSv4 does not	use the	mount protocol,	the
     "administrative controls" are not applied.	 Thus, all the above export
     line(s) should be considered to have the -alldirs flag, even if the line
     is	specified without it.  The third form has the string ``V4:'' followed
     by	a single absolute path name, to	specify	the NFSv4 tree root.  This
     line does not export any file system, but simply marks where the root of
     the server's directory tree is for	NFSv4 clients.	The exported file sys-
     tems for NFSv4 are	specified via the other	lines in the exports(5)	file
     in	the same way as	for NFSv2 and NFSv3.  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 ex-
     ported 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.  For the NFSv4 tree root, the only	option
     that can be specified in this section is -sec.

     Export options are	specified as follows:

     -maproot=user The credential of the specified user	is used	for remote ac-
     cess 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 el-
     ements 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.

     -sec=flavor1:flavor2... specifies a colon separated list of acceptable
     security flavors to be used for remote access.  Supported security	fla-
     vors are sys, krb5, krb5i and krb5p.  If multiple flavors are listed,
     they should be ordered with the most preferred flavor first.  If this op-
     tion is not present, the default security flavor list of just sys is

     The -ro option specifies that the file system should be exported read-
     only (default read/write).	 The option -o is a synonym for	-ro in an ef-
     fort 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.  Note that only one	file
     system can	be WebNFS exported on a	server.

     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 er-
     ror 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 subnet-
     work.  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)).  See	the EXAMPLES section below.

     Scoped IPv6 address must carry scope identifier as	documented in
     inet6(4).	For example, "fe80::%re2/10" is	used to	specify	fe80::/10 on
     re2 interface.

     For the third form	which specifies	the NFSv4 tree root, the directory
     path specifies the	location within	the server's file system tree which is
     the root of the NFSv4 tree.  All entries of this form must	specify	the
     same directory path.  This	location can be	any directory and does not
     need to be	within an exported file	system.	If it is not in	an exported
     file system, a very limited set of	operations are permitted, so that an
     NFSv4 client can traverse the tree	to an exported file system.  Although
     parts of the NFSv4	tree can be non-exported, the entire NFSv4 tree	must
     consist of	local file systems capable of being exported via NFS.  NFSv4
     does not use the mount protocol and does permit clients to	cross server
     mount point boundaries, although not all clients are capable of crossing
     the mount points.

     The -sec option on	these line(s) specifies	what security flavors may be
     used for NFSv4 operations that do not use file handles. Since these oper-
     ations (SetClientID, SetClientIDConfirm, Renew, DelegPurge	and Release-
     LockOnwer)	allocate/modify	state in the server, it	is possible to re-
     strict some clients to the	use of the krb5[ip] security flavors, via this
     option.  See the EXAMPLES section below.  This third form is meaningless
     for NFSv2 and NFSv3 and is	ignored	for them.

     The mountd(8) utility can be made to re-read the exports file by sending
     it	a hangup signal	as follows:

	   /etc/rc.d/mountd reload

     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
	   /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	-network cis-net -mask cis-mask
	   /cdrom -alldirs,quiet,ro -network -mask
	   /private -sec=krb5i
	   /secret -sec=krb5p
	   V4: /   -sec=krb5:krb5i:krb5p -network 131.104.48 -mask
	   V4: /   -sec=sys:krb5:krb5i:krb5p

     Given that	/usr, /u, /a and /u2 are local file system mount points, the
     above example specifies the following:

     The file system rooted at /usr is exported	to hosts friends where friends
     is	specified in the netgroup file with users mapped to their remote cre-
     dentials 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 with users	mapped
     to	their remote credentials and root mapped to the	user and groups	asso-
     ciated 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

     The file system rooted at /u is exported to all hosts on the subnetwork
     131.104.48	with root mapped to the	UID for	"bin" and with no group	ac-

     The file system rooted at /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

     The file system rooted at /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 nota-

     The file system rooted at /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 ad-
     dresses, the -mask	option must not	be used.

     The file system rooted at /cdrom will be exported read-only to the	entire
     network, 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	sup-
     press the error message for this condition	that would normally be sys-
     logged.  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 op-
     tion, 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.

     The file system rooted at /private	will be	exported using Kerberos	5 au-
     thentication and will require integrity protected messages	for all	ac-
     cesses.  The file system rooted at	/secret	will also be exported using
     Kerberos 5	authentication and all messages	used to	access it will be en-

     For the experimental server, the NFSv4 tree is rooted at ``/'', and any
     client within the 131.104.48 subnet is permitted to perform NFSv4 state
     operations	on the server, so long as valid	Kerberos credentials are pro-
     vided.  The machine	is permitted to	perform	NFSv4
     state operations on the server using AUTH_SYS credentials,	as well	as
     Kerberos ones.

     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.

BSD				 July 12, 2011				   BSD


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