xref: /freebsd/sbin/mount_nfs/mount_nfs.8 (revision c98323078dede7579020518ec84cdcb478e5c142)
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28.\"	@(#)mount_nfs.8	8.3 (Berkeley) 3/29/95
29.\" $FreeBSD$
30.\"
31.Dd May 11, 2003
32.Dt MOUNT_NFS 8
33.Os
34.Sh NAME
35.Nm mount_nfs
36.Nd mount NFS file systems
37.Sh SYNOPSIS
38.Nm
39.Op Fl 23NPTUbcdiLls
40.Op Fl D Ar deadthresh
41.Op Fl I Ar readdirsize
42.Op Fl R Ar retrycnt
43.Op Fl a Ar maxreadahead
44.Op Fl g Ar maxgroups
45.Op Fl o Ar options
46.Op Fl r Ar readsize
47.Op Fl t Ar timeout
48.Op Fl w Ar writesize
49.Op Fl x Ar retrans
50.Ar rhost : Ns Ar path node
51.Sh DESCRIPTION
52The
53.Nm
54utility calls the
55.Xr mount 2
56system call to prepare and graft a remote NFS file system
57.Pq Ar rhost : Ns Ar path
58on to the file system tree at the point
59.Ar node .
60This command is normally executed by
61.Xr mount 8 .
62It implements the mount protocol as described in RFC 1094, Appendix A and
63.%T "NFS: Network File System Version 3 Protocol Specification" ,
64Appendix I.
65.Pp
66By default,
67.Nm
68keeps retrying until the mount succeeds.
69This behaviour is intended for file systems listed in
70.Xr fstab 5
71that are critical to the boot process.
72For non-critical file systems, the
73.Fl b
74and
75.Fl R
76flags provide mechanisms to prevent the boot process from hanging
77if the server is unavailable.
78.Pp
79If the server becomes unresponsive while an NFS file system is
80mounted, any new or outstanding file operations on that file system
81will hang uninterruptibly until the server comes back.
82To modify this default behaviour, see the
83.Fl i
84and
85.Fl s
86flags.
87.Pp
88The options are:
89.Bl -tag -width indent
90.It Fl 2
91Use the NFS Version 2 protocol (the default is to try version 3 first
92then version 2).
93Note that NFS version 2 has a file size limit of 2 gigabytes.
94.It Fl 3
95Use the NFS Version 3 protocol.
96.It Fl D
97Set the
98.Dq "dead server threshold"
99to the specified number of round trip timeout intervals before a
100.Dq "server not responding"
101message is displayed.
102.It Fl I
103Set the readdir read size to the specified value.
104The value should normally
105be a multiple of
106.Dv DIRBLKSIZ
107that is <= the read size for the mount.
108.It Fl L
109Do
110.Em not
111forward
112.Xr fcntl 2
113locks over the wire.
114All locks will be local and not seen by the server
115and likewise not seen by other NFS clients.
116This removes the need to run the
117.Xr rpcbind 8
118service and the
119.Xr rpc.statd 8
120and
121.Xr rpc.lockd 8
122servers on the client.
123Note that this option will only be honored when performing the
124initial mount, it will be silently ignored if used while updating
125the mount options.
126.It Fl N
127Do
128.Em not
129use a reserved socket port number (see below).
130.It Fl P
131Use a reserved socket port number.
132This flag is obsolete, and only retained for compatibility reasons.
133Reserved port numbers are used by default now.
134(For the rare case where the client has a trusted root account
135but untrustworthy users and the network cables are in secure areas this does
136help, but for normal desktop clients this does not apply.)
137.It Fl R
138Set the mount retry count to the specified value.
139The default is a retry count of zero, which means to keep retrying
140forever.
141There is a 60 second delay between each attempt.
142.It Fl T
143Use TCP transport instead of UDP.
144This is recommended for servers that are not on the same LAN cable as
145the client.
146(NB: This is NOT supported by most
147.No non- Ns Bx
148servers.)
149.It Fl U
150Force the mount protocol to use UDP transport, even for TCP NFS mounts.
151(Necessary for some old
152.Bx
153servers.)
154.It Fl a
155Set the read-ahead count to the specified value.
156This may be in the range of 0 - 4, and determines how many blocks
157will be read ahead when a large file is being read sequentially.
158Trying a value greater than 1 for this is suggested for
159mounts with a large bandwidth * delay product.
160.It Fl b
161If an initial attempt to contact the server fails, fork off a child to keep
162trying the mount in the background.
163Useful for
164.Xr fstab 5 ,
165where the file system mount is not critical to multiuser operation.
166.It Fl c
167For UDP mount points, do not do a
168.Xr connect 2 .
169This must be used if the server does not reply to requests from the standard
170NFS port number 2049 or replies to requests using a different IP address
171(which can occur if the server is multi-homed).
172Setting the
173.Va vfs.nfs.nfs_ip_paranoia
174sysctl to 0 will make this option the default.
175.It Fl d
176Turn off the dynamic retransmit timeout estimator.
177This may be useful for UDP mounts that exhibit high retry rates,
178since it is possible that the dynamically estimated timeout interval is too
179short.
180.It Fl g
181Set the maximum size of the group list for the credentials to the
182specified value.
183This should be used for mounts on old servers that cannot handle a
184group list size of 16, as specified in RFC 1057.
185Try 8, if users in a lot of groups cannot get response from the mount
186point.
187.It Fl i
188Make the mount interruptible, which implies that file system calls that
189are delayed due to an unresponsive server will fail with EINTR when a
190termination signal is posted for the process.
191.It Fl l
192Used with NQNFS and NFSV3 to specify that the \fBReaddirPlus\fR RPC should
193be used.
194This option reduces RPC traffic for cases such as
195.Dq "ls -l" ,
196but tends to flood the attribute and name caches with prefetched entries.
197Try this option and see whether performance improves or degrades.
198Probably
199most useful for client to server network interconnects with a large bandwidth
200times delay product.
201.It Fl o
202Options are specified with a
203.Fl o
204flag followed by a comma separated string of options.
205See the
206.Xr mount 8
207man page for possible options and their meanings.
208The following NFS specific options are also available:
209.Bl -tag -width indent
210.It Cm port Ns = Ns Aq Ar port_number
211Use specified port number for NFS requests.
212The default is to query the portmapper for the NFS port.
213.It Cm acregmin Ns = Ns Aq Ar seconds
214.It Cm acregmax Ns = Ns Aq Ar seconds
215.It Cm acdirmin Ns = Ns Aq Ar seconds
216.It Cm acdirmax Ns = Ns Aq Ar seconds
217When attributes of files are cached, a timeout calculated to determine
218whether a given cache entry has expired.
219These four values determine the upper and lower bounds of the timeouts for
220.Dq directory
221attributes and
222.Dq regular
223(ie: everything else).
224The default values are 3 -> 60 seconds
225for regular files, and 30 -> 60 seconds for directories.
226The algorithm to calculate the timeout is based on the age of the file.
227The older the file,
228the longer the cache is considered valid, subject to the limits above.
229.It Cm noinet4 , noinet6
230Disables
231.Dv AF_INET
232or
233.Dv AF_INET6
234connections.
235Useful for hosts that have
236both an A record and an AAAA record for the same name.
237.El
238.Pp
239.Sy Historic Fl o Sy Options
240.Pp
241Use of these options is deprecated, they are only mentioned here for
242compatibility with historic versions of
243.Nm .
244.Bl -tag -width ".Cm dumbtimer"
245.It Cm bg
246Same as
247.Fl b .
248.It Cm conn
249Same as not specifying
250.Fl c .
251.It Cm dumbtimer
252Same as
253.Fl d .
254.It Cm intr
255Same as
256.Fl i .
257.It Cm lockd
258Same as not specifying
259.Fl L .
260.It Cm nfsv2
261Same as
262.Fl 2 .
263.It Cm nfsv3
264Same as
265.Fl 3 .
266.It Cm rdirplus
267Same as
268.Fl l .
269.It Cm mntudp
270Same as
271.Fl U .
272.It Cm resvport
273Same as
274.Fl P .
275.It Cm soft
276Same as
277.Fl s .
278.It Cm tcp
279Same as
280.Fl T .
281.El
282.It Fl r
283Set the read data size to the specified value.
284It should normally be a power of 2 greater than or equal to 1024.
285This should be used for UDP mounts when the
286.Dq "fragments dropped due to timeout"
287value is getting large while actively using a mount point.
288(Use
289.Xr netstat 1
290with the
291.Fl s
292option to see what the
293.Dq "fragments dropped due to timeout"
294value is.)
295See the
296.Fl w
297option as well.
298.It Fl s
299A soft mount, which implies that file system calls will fail
300after
301.Ar retrycnt
302round trip timeout intervals.
303.It Fl t
304Set the initial retransmit timeout to the specified value.
305May be useful for fine tuning UDP mounts over internetworks
306with high packet loss rates or an overloaded server.
307Try increasing the interval if
308.Xr nfsstat 1
309shows high retransmit rates while the file system is active or reducing the
310value if there is a low retransmit rate but long response delay observed.
311(Normally, the
312.Fl d
313option should be specified when using this option to manually
314tune the timeout
315interval.)
316.It Fl w
317Set the write data size to the specified value.
318Ditto the comments w.r.t.\& the
319.Fl r
320option, but using the
321.Dq "fragments dropped due to timeout"
322value on the server instead of the client.
323Note that both the
324.Fl r
325and
326.Fl w
327options should only be used as a last ditch effort at improving performance
328when mounting servers that do not support TCP mounts.
329.It Fl x
330Set the retransmit timeout count for soft mounts to the specified value.
331.El
332.Sh SEE ALSO
333.Xr mount 2 ,
334.Xr unmount 2 ,
335.Xr fstab 5 ,
336.Xr mount 8 ,
337.Xr nfsd 8 ,
338.Xr nfsiod 8 ,
339.Xr showmount 8
340.Sh BUGS
341Due to the way that Sun RPC is implemented on top of UDP (unreliable datagram)
342transport, tuning such mounts is really a black art that can only be expected
343to have limited success.
344For clients mounting servers that are not on the same
345LAN cable or that tend to be overloaded,
346TCP transport is strongly recommended,
347but unfortunately this is restricted to mostly
348.Bx 4.4
349servers.
350