1 .\" nfs.5 "Rick Sladkey" <jrs@world.std.com>
2 .\" Wed Feb 8 12:52:42 1995, faith@cs.unc.edu: updates for Ross Biro's
4 .TH NFS 5 "20 November 1993" "Linux 0.99" "Linux Programmer's Manual"
6 nfs \- nfs and nfs4 fstab format and options
12 file contains information about which filesystems
13 to mount where and with what options.
14 For NFS mounts, it contains the server name and
15 exported server directory to mount from,
16 the local directory that is the mount point,
17 and the NFS specific options that control
18 the way the filesystem is mounted.
20 Three different versions of the NFS protocol are
21 supported by the Linux NFS client:
22 NFS version 2, NFS version 3, and NFS version 4.
23 To mount via NFS version 2, use the
25 file system type and specify
27 To mount via NFS version 3, use the
29 file system type and specify
31 Version 3 is the default protocol version for the
35 is not specified on the mount command and both client and server
37 To mount via NFS version 4, use the
42 keyword is not supported for the
46 These file system types share similar mount options;
47 the differences are listed below.
49 Here is an example from an \fI/etc/fstab\fP file for an NFSv3 mount
53 .ta 2.5i +0.75i +0.75i +1.0i
54 server:/usr/local/pub /pub nfs rsize=32768,wsize=32768,timeo=14,intr
57 Here is an example for an NFSv4 mount over TCP using Kerberos
58 5 mutual authentication.
61 .ta 2.5i +0.75i +0.75i +1.0i
62 server:/usr/local/pub /pub nfs4 proto=tcp,sec=krb5,hard,intr
65 .SS Options for the nfs file system type
68 The number of bytes NFS uses when reading files from an NFS server.
69 The rsize is negotiated between the server and client to determine
70 the largest block size that both can support.
71 The value specified by this option is the maximum size that could
72 be used; however, the actual size used may be smaller.
73 Note: Setting this size to a value less than the largest supported
74 block size will adversely affect performance.
77 The number of bytes NFS uses when writing files to an NFS server.
78 The wsize is negotiated between the server and client to determine
79 the largest block size that both can support.
80 The value specified by this option is the maximum size that could
81 be used; however, the actual size used may be smaller.
82 Note: Setting this size to a value less than the largest supported
83 block size will adversely affect performance.
86 The value in tenths of a second before sending the
87 first retransmission after an RPC timeout.
88 The default value is 7 tenths of a second. After the first timeout,
89 the timeout is doubled after each successive timeout until a maximum
90 timeout of 60 seconds is reached or the enough retransmissions
91 have occured to cause a major timeout. Then, if the filesystem
92 is hard mounted, each new timeout cascade restarts at twice the
93 initial value of the previous cascade, again doubling at each
94 retransmission. The maximum timeout is always 60 seconds.
95 Better overall performance may be achieved by increasing the
96 timeout when mounting on a busy network, to a slow server, or through
97 several routers or gateways.
100 The number of minor timeouts and retransmissions that must occur before
101 a major timeout occurs. The default is 3 timeouts. When a major timeout
102 occurs, the file operation is either aborted or a "server not responding"
103 message is printed on the console.
106 The minimum time in seconds that attributes of a regular file should
107 be cached before requesting fresh information from a server.
108 The default is 3 seconds.
111 The maximum time in seconds that attributes of a regular file can
112 be cached before requesting fresh information from a server.
113 The default is 60 seconds.
116 The minimum time in seconds that attributes of a directory should
117 be cached before requesting fresh information from a server.
118 The default is 30 seconds.
121 The maximum time in seconds that attributes of a directory can
122 be cached before requesting fresh information from a server.
123 The default is 60 seconds.
126 Using actimeo sets all of
133 There is no default value.
136 The number of minutes to retry an NFS mount operation
137 in the foreground or background before giving up.
138 The default value for forground mounts is 2 minutes.
139 The default value for background mounts is 10000 minutes,
140 which is roughly one week.
143 When an NFS server does not support version two of the
144 RPC mount protocol, this option can be used to specify
145 the maximum length of a filename that is supported on
146 the remote filesystem. This is used to support the
147 POSIX pathconf functions. The default is 255 characters.
150 The numeric value of the port to connect to the NFS server on.
151 If the port number is 0 (the default) then query the
152 remote host's portmapper for the port number to use.
153 If the remote host's NFS daemon is not registered with
154 its portmapper, the standard NFS port number 2049 is
158 The numeric value of the
163 The name of the host running
167 Use an alternate RPC program number to contact the
168 mount daemon on the remote host. This option is useful
169 for hosts that can run multiple NFS servers.
170 The default value is 100005 which is the standard RPC
171 mount daemon program number.
174 Use an alternate RPC version number to contact the
175 mount daemon on the remote host. This option is useful
176 for hosts that can run multiple NFS servers.
177 The default value depends on which kernel you are using.
180 Use an alternate RPC program number to contact the
181 NFS daemon on the remote host. This option is useful
182 for hosts that can run multiple NFS servers.
183 The default value is 100003 which is the standard RPC
184 NFS daemon program number.
187 Use an alternate RPC version number to contact the
188 NFS daemon on the remote host. This option is useful
189 for hosts that can run multiple NFS servers.
190 The default value depends on which kernel you are using.
193 vers is an alternative to nfsvers and is compatible with
194 many other operating systems.
197 Disable NFS locking. Do not start lockd.
198 This is appropriate for mounting the root filesystem or
202 These filesystems are typically either read-only or not shared, and in
203 those cases, remote locking is not needed.
204 This also needs to be used with some old NFS servers
205 that don't support locking.
207 Note that applications can still get locks on files, but the locks
208 only provide exclusion locally. Other clients mounting the same
209 filesystem will not be able to detect the locks.
212 If the first NFS mount attempt times out, retry the mount
214 After a mount operation is backgrounded, all subsequent mounts
215 on the same NFS server will be backgrounded immediately, without
216 first attempting the mount.
217 A missing mount point is treated as a timeout,
218 to allow for nested NFS mounts.
221 If the first NFS mount attempt times out, retry the mount
223 This is the complement of the
225 option, and also the default behavior.
228 If an NFS file operation has a major timeout then report an I/O error to
230 The default is to continue retrying NFS file operations indefinitely.
233 If an NFS file operation has a major timeout then report
234 "server not responding" on the console and continue retrying indefinitely.
238 If an NFS file operation has a major timeout and it is hard mounted,
239 then allow signals to interupt the file operation and cause it to
240 return EINTR to the calling program. The default is to not
241 allow file operations to be interrupted.
244 Mount the NFS filesystem using POSIX semantics. This allows
245 an NFS filesystem to properly support the POSIX pathconf
246 command by querying the mount server for the maximum length
247 of a filename. To do this, the remote host must support version
248 two of the RPC mount protocol. Many NFS servers support only
252 Suppress the retrieval of new attributes when creating a file.
255 Disable all forms of attribute caching entirely. This extracts a
256 significant performance penalty but it allows two different NFS clients
257 to get reasonable results when both clients are actively
258 writing to a common export on the server.
261 Disables Access Control List (ACL) processing.
264 Set the security flavor for this mount to "mode".
265 The default setting is \f3sec=sys\f1, which uses local
266 unix uids and gids to authenticate NFS operations (AUTH_SYS).
267 Other currently supported settings are:
268 \f3sec=krb5\f1, which uses Kerberos V5 instead of local unix uids
269 and gids to authenticate users;
270 \f3sec=krb5i\f1, which uses Kerberos V5 for user authentication
271 and performs integrity checking of NFS operations using secure
272 checksums to prevent data tampering; and
273 \f3sec=krb5p\f1, which uses Kerberos V5 for user authentication
274 and integrity checking, and encrypts NFS traffic to prevent
275 traffic sniffing (this is the most secure setting).
276 Note that there is a performance penalty when using integrity
280 Mount the NFS filesystem using the TCP protocol. This is the default
281 if it is supported by both client and server. Many NFS servers only
285 Mount the NFS filesystem using the UDP protocol.
288 Disables NFSv3 READDIRPLUS RPCs. Use this option when
289 mounting servers that don't support or have broken
290 READDIRPLUS implementations.
292 All of the non-value options have corresponding nooption forms.
293 For example, nointr means don't allow file operations to be
295 .SS Options for the nfs4 file system type
298 The number of bytes nfs4 uses when reading files from the server.
299 The rsize is negotiated between the server and client to determine
300 the largest block size that both can support.
301 The value specified by this option is the maximum size that could
302 be used; however, the actual size used may be smaller.
303 Note: Setting this size to a value less than the largest supported
304 block size will adversely affect performance.
307 The number of bytes nfs4 uses when writing files to the server.
308 The wsize is negotiated between the server and client to determine
309 the largest block size that both can support.
310 The value specified by this option is the maximum size that could
311 be used; however, the actual size used may be smaller.
312 Note: Setting this size to a value less than the largest supported
313 block size will adversely affect performance.
316 The value in tenths of a second before sending the
317 first retransmission after an RPC timeout.
318 The default value depends on whether
322 is in effect (see below).
323 The default value for UDP is 7 tenths of a second.
324 The default value for TCP is 60 seconds.
325 After the first timeout,
326 the timeout is doubled after each successive timeout until a maximum
327 timeout of 60 seconds is reached or the enough retransmissions
328 have occured to cause a major timeout. Then, if the filesystem
329 is hard mounted, each new timeout cascade restarts at twice the
330 initial value of the previous cascade, again doubling at each
331 retransmission. The maximum timeout is always 60 seconds.
334 The number of minor timeouts and retransmissions that must occur before
335 a major timeout occurs. The default is 5 timeouts for
340 occurs, the file operation is either aborted or a "server not responding"
341 message is printed on the console.
344 The minimum time in seconds that attributes of a regular file should
345 be cached before requesting fresh information from a server.
346 The default is 3 seconds.
349 The maximum time in seconds that attributes of a regular file can
350 be cached before requesting fresh information from a server.
351 The default is 60 seconds.
354 The minimum time in seconds that attributes of a directory should
355 be cached before requesting fresh information from a server.
356 The default is 30 seconds.
359 The maximum time in seconds that attributes of a directory can
360 be cached before requesting fresh information from a server.
361 The default is 60 seconds.
364 Using actimeo sets all of
371 There is no default value.
374 The number of minutes to retry an NFS mount operation
375 in the foreground or background before giving up.
376 The default value for forground mounts is 2 minutes.
377 The default value for background mounts is 10000 minutes,
378 which is roughly one week.
381 The numeric value of the port to connect to the NFS server on.
382 If the port number is 0 (the default) then query the
383 remote host's portmapper for the port number to use.
384 If the remote host's NFS daemon is not registered with
385 its portmapper, the standard NFS port number 2049 is
389 Mount the NFS filesystem using a specific network protocol
390 instead of the default UDP protocol.
391 Many NFS version 4 servers only support TCP.
392 Valid protocol types are
398 On a multi-homed client, this
399 causes the client to use a specific callback address when
400 communicating with an NFS version 4 server.
401 This option is currently ignored.
404 Same as \f3sec=mode\f1 for the nfs filesystem type (see above).
407 If an NFS mount attempt times out, retry the mount
409 After a mount operation is backgrounded, all subsequent mounts
410 on the same NFS server will be backgrounded immediately, without
411 first attempting the mount.
412 A missing mount point is treated as a timeout,
413 to allow for nested NFS mounts.
416 If the first NFS mount attempt times out, retry the mount
418 This is the complement of the
420 option, and also the default behavior.
423 If an NFS file operation has a major timeout then report an I/O error to
425 The default is to continue retrying NFS file operations indefinitely.
428 If an NFS file operation has a major timeout then report
429 "server not responding" on the console and continue retrying indefinitely.
433 If an NFS file operation has a major timeout and it is hard mounted,
434 then allow signals to interupt the file operation and cause it to
435 return EINTR to the calling program. The default is to not
436 allow file operations to be interrupted.
439 Suppress the retrieval of new attributes when creating a file.
442 Disable attribute caching, and force synchronous writes.
444 server performance penalty but it allows two different NFS clients
445 to get reasonable good results when both clients are actively
446 writing to common filesystem on the server.
448 All of the non-value options have corresponding nooption forms.
449 For example, nointr means don't allow file operations to be
454 .BR fstab "(5), " mount "(8), " umount "(8), " exports (5)
456 "Rick Sladkey" <jrs@world.std.com>
459 Checking files on NFS filesystem referenced by file descriptors (i.e. the
463 families of functions) may lead to inconsistent result due to the lack of
464 consistency check in kernel even if noac is used.