3 .TH exports 5 "31 December 2009"
5 exports \- NFS server export table
9 contains a table of local physical file systems on an NFS server
10 that are accessible to NFS clients.
11 The contents of the file are maintained by the server's system
14 Each file system in this table has a list of options and an
18 to give information to
21 The file format is similar to the SunOS
23 file. Each line contains an export point and a whitespace-separated list
24 of clients allowed to mount the file system at that point. Each listed
25 client may be immediately followed by a parenthesized, comma-separated
26 list of export options for that client. No whitespace is permitted
27 between a client and its option list.
29 Also, each line may have one or more specifications for default options
30 after the path name, in the form of a dash ("\-") followed by an option
31 list. The option list is used for all subsequent exports on that line
34 Blank lines are ignored. A pound sign ("#") introduces a comment to the
35 end of the line. Entries may be continued across newlines using a
36 backslash. If an export name contains spaces it should be quoted using
37 double quotes. You can also specify spaces or other unusual character in
38 the export name using a backslash followed by the character code as three
41 To apply changes to this file, run
43 or restart the NFS server.
45 .SS Machine Name Formats
46 NFS clients may be specified in a number of ways:
48 You may specify a host either by an
49 abbreviated name recognized be the resolver, the fully qualified domain
50 name, an IPv4 address, or an IPv6 address.
52 You can also export directories to all hosts on an IP (sub-) network
53 simultaneously. This is done by specifying an IP address and netmask pair
56 where the netmask can be specified in dotted-decimal format, or as a
57 contiguous mask length.
58 For example, either `/255.255.252.0' or `/22' appended
59 to the network base IPv4 address results in identical subnetworks with 10 bits
60 of host. IPv6 addresses must use a contiguous mask length. Wildcard characters
61 generally do not work on IP addresses, though they
62 may work by accident when reverse DNS lookups fail.
64 Machine names may contain the wildcard characters \fI*\fR and \fI?\fR.
65 This can be used to make the \fIexports\fR file more compact; for instance,
66 \fI*.cs.foo.edu\fR matches all hosts in the domain
67 \fIcs.foo.edu\fR. As these characters also match the dots in a domain
68 name, the given pattern will also match all hosts within any subdomain
71 NIS netgroups may be given as
73 Only the host part of each
74 netgroup members is consider in checking for membership. Empty host
75 parts or those containing a single dash (\-) are ignored.
77 This is specified by a single
79 character (not to be confused with the
81 entry above) and will match all clients.
84 '''This is a special ``hostname'' that identifies the given directory name
85 '''as the public root directory (see the section on WebNFS in
87 '''for a discussion of WebNFS and the public root handle). When using this
90 '''must be the only entry on this line, and must have no export options
91 '''associated with it. Note that this does
93 '''actually export the named directory; you still have to set the exports
94 '''options in a separate entry.
96 '''The public root path can also be specified by invoking
99 '''.B \-\-public\-root
100 '''option. Multiple specifications of a public root will be ignored.
102 If a client matches more than one of the specifications above, then
103 the first match from the above list order takes precedence - regardless of
104 the order they appear on the export line. However, if a client matches
105 more than one of the same type of specification (e.g. two netgroups),
106 then the first match from the order they appear on the export line takes
108 .SS RPCSEC_GSS security
109 You may use the special strings "gss/krb5", "gss/krb5i", or "gss/krb5p"
110 to restrict access to clients using rpcsec_gss security. However, this
111 syntax is deprecated; on linux kernels since 2.6.23, you should instead
112 use the "sec=" export option:
115 The sec= option, followed by a colon-delimited list of security flavors,
116 restricts the export to clients using those flavors. Available security
117 flavors include sys (the default--no cryptographic security), krb5
118 (authentication only), krb5i (integrity protection), and krb5p (privacy
119 protection). For the purposes of security flavor negotiation, order
120 counts: preferred flavors should be listed first. The order of the sec=
121 option with respect to the other options does not matter, unless you
122 want some options to be enforced differently depending on flavor.
123 In that case you may include multiple sec= options, and following options
124 will be enforced only for access using flavors listed in the immediately
125 preceding sec= option. The only options that are permitted to vary in
126 this way are ro, rw, no_root_squash, root_squash, and all_squash.
130 understands the following export options:
133 This option requires that requests originate on an Internet port less
134 than IPPORT_RESERVED (1024). This option is on by default. To turn it
139 Allow both read and write requests on this NFS volume. The
140 default is to disallow any request which changes the filesystem.
141 This can also be made explicit by using
146 This option allows the NFS server to violate the NFS protocol and
147 reply to requests before any changes made by that request have been
148 committed to stable storage (e.g. disc drive).
150 Using this option usually improves performance, but at the cost that
151 an unclean server restart (i.e. a crash) can cause data to be lost or
156 Reply to requests only after the changes have been committed to stable
161 In releases of nfs-utils up to and including 1.0.0, the
164 default. In all releases after 1.0.0,
168 must be explicitly requested if needed.
169 To help make system administrators aware of this change,
171 will issue a warning if neither
178 This option has no effect if
180 is also set. The NFS server will normally delay committing a write request
181 to disc slightly if it suspects that another related write request may be in
182 progress or may arrive soon. This allows multiple write requests to
183 be committed to disc with the one operation which can improve
184 performance. If an NFS server received mainly small unrelated
185 requests, this behaviour could actually reduce performance, so
187 is available to turn it off.
188 The default can be explicitly requested with the
192 This option is based on the option of the same name provided in IRIX
193 NFS. Normally, if a server exports two filesystems one of which is
194 mounted on the other, then the client will have to mount both
195 filesystems explicitly to get access to them. If it just mounts the
196 parent, it will see an empty directory at the place where the other
197 filesystem is mounted. That filesystem is "hidden".
201 option on a filesystem causes it not to be hidden, and an
202 appropriately authorised client will be able to move from the parent to
203 that filesystem without noticing the change.
205 However, some NFS clients do not cope well with this situation as, for
206 instance, it is then possible for two files in the one apparent
207 filesystem to have the same inode number.
211 option is currently only effective on
213 exports. It does not work reliably with netgroup, subnet, or wildcard
216 This option can be very useful in some situations, but it should be
217 used with due care, and only after confirming that the client system
218 copes with the situation effectively.
220 The option can be explicitly disabled with
224 This option is similar to
226 but it makes it possible for clients to move from the filesystem marked
227 with crossmnt to exported filesystems mounted on it. Thus when a child
228 filesystem "B" is mounted on a parent "A", setting crossmnt on "A" has
229 the same effect as setting "nohide" on B.
232 This option disables subtree checking, which has mild security
233 implications, but can improve reliability in some circumstances.
235 If a subdirectory of a filesystem is exported, but the whole
236 filesystem isn't then whenever a NFS request arrives, the server must
237 check not only that the accessed file is in the appropriate filesystem
238 (which is easy) but also that it is in the exported tree (which is
239 harder). This check is called the
242 In order to perform this check, the server must include some
243 information about the location of the file in the "filehandle" that is
244 given to the client. This can cause problems with accessing files that
245 are renamed while a client has them open (though in many simple cases
248 subtree checking is also used to make sure that files inside
249 directories to which only root has access can only be accessed if the
250 filesystem is exported with
252 (see below), even if the file itself allows more general access.
254 As a general guide, a home directory filesystem, which is normally
255 exported at the root and may see lots of file renames, should be
256 exported with subtree checking disabled. A filesystem which is mostly
257 readonly, and at least doesn't see many file renames (e.g. /usr or
258 /var) and for which subdirectories may be exported, should probably be
259 exported with subtree checks enabled.
261 The default of having subtree checks enabled, can be explicitly
265 From release 1.1.0 of nfs-utils onwards, the default will be
267 as subtree_checking tends to cause more problems than it is worth.
268 If you genuinely require subtree checking, you should explicitly put
271 file. If you put neither option,
273 will warn you that the change is pending.
279 This option (the two names are synonymous) tells the NFS server not to require authentication of
280 locking requests (i.e. requests which use the NLM protocol). Normally
281 the NFS server will require a lock request to hold a credential for a
282 user who has read access to the file. With this flag no access checks
285 Early NFS client implementations did not send credentials with lock
286 requests, and many current NFS clients still exist which are based on
287 the old implementations. Use this flag if you find that you can only
288 lock files which are world readable.
290 The default behaviour of requiring authentication for NLM requests can
291 be explicitly requested with either of the synonymous
297 On some specially patched kernels, and when exporting filesystems that
298 support ACLs, this option tells
300 not to reveal ACLs to clients, so
301 they will see only a subset of actual permissions on the given file
302 system. This option is safe for filesystems used by NFSv2 clients and
303 old NFSv3 clients that perform access decisions locally. Current
304 NFSv3 clients use the ACCESS RPC to perform all access decisions on
305 the server. Note that the
307 option only has effect on kernels specially patched to support it, and
308 when exporting filesystems with ACL support. The default is to export
309 with ACL support (i.e. by default,
315 '''This makes everything below the directory inaccessible for the named
316 '''client. This is useful when you want to export a directory hierarchy to
317 '''a client, but exclude certain subdirectories. The client's view of a
318 '''directory flagged with noaccess is very limited; it is allowed to read
319 '''its attributes, and lookup `.' and `..'. These are also the only entries
320 '''returned by a readdir.
323 '''Convert absolute symbolic links (where the link contents start with a
324 '''slash) into relative links by prepending the necessary number of ../'s
325 '''to get from the directory containing the link to the root on the
326 '''server. This has subtle, perhaps questionable, semantics when the file
327 '''hierarchy is not mounted at its root.
330 '''Leave all symbolic link as they are. This is the default operation.
336 This option makes it possible to only export a directory if it has
337 successfully been mounted.
338 If no path is given (e.g.
339 .IR mountpoint " or " mp )
340 then the export point must also be a mount point. If it isn't then
341 the export point is not exported. This allows you to be sure that the
342 directory underneath a mountpoint will never be exported by accident
343 if, for example, the filesystem failed to mount due to a disc error.
345 If a path is given (e.g.
346 .IR mountpoint= "/path or " mp= /path)
347 then the nominated path must be a mountpoint for the exportpoint to be
351 .IR fsid= num|root|uuid
352 NFS needs to be able to identify each filesystem that it exports.
353 Normally it will use a UUID for the filesystem (if the filesystem has
354 such a thing) or the device number of the device holding the
355 filesystem (if the filesystem is stored on the device).
357 As not all filesystems are stored on devices, and not all filesystems
358 have UUIDs, it is sometimes necessary to explicitly tell NFS how to
359 identify a filesystem. This is done with the
363 For NFSv4, there is a distinguished filesystem which is the root of
364 all exported filesystem. This is specified with
368 both of which mean exactly the same thing.
370 Other filesystems can be identified with a small integer, or a UUID
371 which should contain 32 hex digits and arbitrary punctuation.
373 Linux kernels version 2.6.20 and earlier do not understand the UUID
374 setting so a small integer must be used if an fsid option needs to be
375 set for such kernels. Setting both a small number and a UUID is
376 supported so the same configuration can be made to work on old and new
380 .IR refer= path@host[+host][:path@host[+host]]
381 A client referencing the export point will be directed to choose from
382 the given list an alternative location for the filesystem.
383 (Note that the server must have a mountpoint here, though a different
384 filesystem is not required; so, for example,
385 .IR "mount --bind" " /path /path"
388 .IR replicas= path@host[+host][:path@host[+host]]
389 If the client asks for alternative locations for the export point, it
390 will be given this list of alternatives. (Note that actual replication
391 of the filesystem must be handled elsewhere.)
396 bases its access control to files on the server machine on the uid and
397 gid provided in each NFS RPC request. The normal behavior a user would
398 expect is that she can access her files on the server just as she would
399 on a normal file system. This requires that the same uids and gids are
400 used on the client and the server machine. This is not always true, nor
401 is it always desirable.
403 Very often, it is not desirable that the root user on a client machine
404 is also treated as root when accessing files on the NFS server. To this
405 end, uid 0 is normally mapped to a different id: the so-called
408 uid. This mode of operation (called `root squashing') is the default,
409 and can be turned off with
414 '''tries to obtain the anonymous uid and gid by looking up user
416 '''in the password file at startup time. If it isn't found, a uid and gid
418 chooses a uid and gid
419 of 65534 for squashed access. These values can also be overridden by
421 .IR anonuid " and " anongid
424 '''In addition to this,
426 '''lets you specify arbitrary uids and gids that should be mapped to user
428 Finally, you can map all user requests to the
429 anonymous uid by specifying the
430 .IR all_squash " option.
432 Here's the complete list of mapping options:
435 Map requests from uid/gid 0 to the anonymous uid/gid. Note that this does
436 not apply to any other uids or gids that might be equally sensitive, such as
443 Turn off root squashing. This option is mainly useful for diskless clients.
446 Map all uids and gids to the anonymous user. Useful for NFS-exported
447 public FTP directories, news spool directories, etc. The opposite option
450 which is the default setting.
452 .IR anonuid " and " anongid
453 These options explicitly set the uid and gid of the anonymous account.
454 This option is primarily useful for PC/NFS clients, where you might want
455 all requests appear to be from one user. As an example, consider the
458 in the example section below, which maps all requests to uid 150 (which
459 is supposedly that of user joe).
460 .SS Extra Export Tables
466 directory as extra export tables.
468 regards only a file which name is ended with
473 as an extra export file. A file which name
474 is not met this condition is just ignored.
475 The format for extra export tables is the same as
483 # sample /etc/exports file
484 / master(rw) trusty(rw,no_root_squash)
485 /projects proj*.local.domain(rw)
486 /usr *.local.domain(ro) @trusted(rw)
487 /home/joe pc001(rw,all_squash,anonuid=150,anongid=100)
488 /pub *(ro,insecure,all_squash)
489 /srv/www \-sync,rw server @trusted @external(ro)
490 /foo 2001:db8:9:e54::/64(rw) 192.0.2.0/24(rw)
491 '''/pub/private (noaccess)
494 The first line exports the entire filesystem to machines master and trusty.
495 In addition to write access, all uid squashing is turned off for host
496 trusty. The second and third entry show examples for wildcard hostnames
497 and netgroups (this is the entry `@trusted'). The fourth line shows the
498 entry for the PC/NFS client discussed above. Line 5 exports the
499 public FTP directory to every host in the world, executing all requests
500 under the nobody account. The
502 option in this entry also allows clients with NFS implementations that
503 don't use a reserved port for NFS.
504 The sixth line exports a directory read-write to the machine 'server'
505 as well as the `@trusted' netgroup, and read-only to netgroup `@external',
506 all three mounts with the `sync' option enabled. The seventh line exports
507 a directory to both an IPv6 and an IPv4 subnet.
508 ''' The last line denies all NFS clients
509 '''access to the private directory.
511 '''Unlike other NFS server implementations, this
513 '''allows you to export both a directory and a subdirectory thereof to
514 '''the same host, for instance
515 '''.IR /usr " and " /usr/X11R6 .
516 '''In this case, the mount options of the most specific entry apply. For
517 '''instance, when a user on the client host accesses a file in
519 '''the mount options given in the
521 '''entry apply. This is also true when the latter is a wildcard or netgroup
533 '''An error parsing the file is reported using syslogd(8) as level NOTICE from
538 '''is started up. Any unknown
539 '''host is reported at that time, but often not all hosts are not yet known
542 '''at boot time, thus as hosts are found they are reported
projects / nfs-utils.git / blob