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.\"	@(#)mount_nfs.8	8.3 (Berkeley) 3/29/95

.\"

.\" $Id: mount_nfs.8,v 1.14 1998/07/06 07:15:53 charnier Exp $

.\""

.Dd March 29, 1995

.Dt MOUNT_NFS 8

.Os BSD 4.4

.Sh NAME

.Nm mount_nfs

.Nd mount nfs file systems

.Sh SYNOPSIS

.Nm mount_nfs

.Op Fl 23KNPTUbcdilqs

.Op Fl D Ar deadthresh

.Op Fl I Ar readdirsize

.Op Fl L Ar leaseterm

.Op Fl R Ar retrycnt

.Op Fl a Ar maxreadahead

.Op Fl g Ar maxgroups

.Op Fl m Ar realm

.Op Fl o Ar options

.Op Fl r Ar readsize

.Op Fl t Ar timeout

.Op Fl w Ar writesize

.Op Fl x Ar retrans

.Ar rhost:path node

.Sh DESCRIPTION

The

.Nm

command

calls the

.Xr mount 2

system call to prepare and graft a remote nfs file system (rhost:path)

on to the file system tree at the point

.Ar node.

This command is normally executed by

.Xr mount 8 .

It implements the mount protocol as described in RFC 1094, Appendix A and

.%T "NFS: Network File System Version 3 Protocol Specification" ,

Appendix I.

.Pp

The options are:

.Bl -tag -width indent

.It Fl 2

Use the NFS Version 2 protocol (the default is to try version 3 first

then version 2).  Note that NFS version 2 has a file size limit of 2

gigabytes.

.It Fl 3

Use the NFS Version 3 protocol.

.It Fl D

Used with NQNFS to set the

.Dq "dead server threshold"

to the specified number of round trip timeout intervals.

After a

.Dq "dead server threshold"

of retransmit timeouts,

cached data for the unresponsive server is assumed to still be valid.

Values may be set in the range of 1 - 9, with 9 referring to an

.Dq "infinite dead threshold"

(i.e. never assume cached data still valid).

This option is not generally recommended and is really an experimental

feature.

.It Fl I

Set the readdir read size to the specified value. The value should normally

be a multiple of DIRBLKSIZ that is <= the read size for the mount.

.It Fl K

Pass Kerberos authenticators to the server for client-to-server

user-credential mapping.

This requires that the kernel be built with the NFSKERB option.

(Refer to the INTERNET-DRAFT titled

.%T "Authentication Mechanisms for ONC RPC" ,

for more information.)

.It Fl L

Used with NQNFS to set the lease term to the specified number of seconds.

Only use this argument for mounts with a large round trip delay.

Values are normally in the 10-30 second range.

.It Fl N

Do

.Em not

use a reserved socket port number (see below).

.It Fl P

Use a reserved socket port number.

This flag is obsolete, and only retained for compatibility reasons.

Reserved port numbers are used by default now.

This is useful for mounting servers that require clients to use a

reserved port number on the mistaken belief that this makes NFS

more secure. (For the rare case where the client has a trusted root account

but untrustworthy users and the network cables are in secure areas this does

help, but for normal desktop clients this does not apply.)

.It Fl R

Set the retry count for doing the mount to the specified value.

.It Fl T

Use TCP transport instead of UDP.

This is recommended for servers that are not on the same LAN cable as

the client.

(NB: This is NOT supported by most non-BSD servers.)

.It Fl U

Force the mount protocol to use UDP transport, even for TCP NFS mounts.

(Necessary for some old BSD servers.)

.It Fl a

Set the read-ahead count to the specified value.

This may be in the range of 0 - 4, and determines how many blocks

will be read ahead when a large file is being read sequentially.

Trying a value greater than 1 for this is suggested for

mounts with a large bandwidth * delay product.

.It Fl b

If an initial attempt to contact the server fails, fork off a child to keep

trying the mount in the background.

Useful for

.Xr fstab 5 ,

where the filesystem mount is not critical to multiuser operation.

.It Fl c

For UDP mount points, do not do a

.Xr connect 2 .

This must be used for servers that do not reply to requests from the

standard NFS port number 2049.

.It Fl d

Turn off the dynamic retransmit timeout estimator.

This may be useful for UDP mounts that exhibit high retry rates,

since it is possible that the dynamically estimated timeout interval is too

short.

.It Fl g

Set the maximum size of the group list for the credentials to the

specified value.

This should be used for mounts on old servers that cannot handle a

group list size of 16, as specified in RFC 1057.

Try 8, if users in a lot of groups cannot get response from the mount

point.

.It Fl i

Make the mount interruptible, which implies that file system calls that

are delayed due to an unresponsive server will fail with EINTR when a

termination signal is posted for the process.

.It Fl l

Used with NQNFS and NFSV3 to specify that the \fBReaddirPlus\fR RPC should

be used.

This option reduces RPC traffic for cases such as

.Dq "ls -l" ,

but tends to flood the attribute and name caches with prefetched entries.

Try this option and see whether performance improves or degrades. Probably

most useful for client to server network interconnects with a large bandwidth

times delay product.

.It Fl m

Set the Kerberos realm to the string argument.

Used with the

.Fl K

option for mounts to other realms.

.It Fl o

Options are specified with a

.Fl o

flag followed by a comma separated string of options.

See the

.Xr mount 8

man page for possible options and their meanings.

The following NFS specific option is also available:

.Bl -tag -width indent

.It port=<port_number>

Use specified port number for NFS requests.

The default is to query the portmapper for the NFS port.

.It acregmin=<seconds>

.It acregmax=<seconds>

.It acdirmin=<seconds>

.It acdirmax=<seconds>

When attributes of files are cached, a timeout calculated to determine

whether a given cache entry has expired.  These four values determine the

upper and lower bounds of the timeouts for ``directory'' attributes and

``regular'' (ie: everything else).  The default values are 3 -> 60 seconds

for regular files, and 30 -> 60 seconds for directories.  The algorithm to

calculate the timeout is based on the age of the file.  The older the file,

the longer the cache is considered valid, subject to the limits above.

.El

.Pp

.Bl -tag -width "dumbtimerXX"

\fBHistoric \&-o options\fR

.Pp

Use of these options is deprecated, they are only mentioned here for

compatibility with historic versions of

.Nm Ns .

.It bg

Same as

.Fl b .

.It conn

Same as not specifying 

.Fl c .

.It dumbtimer

Same as

.Fl d .

.It intr

Same as

.Fl i .

.It kerb

Same as

.Fl K .

.It nfsv2

Same as

.Fl 2 .

.It nfsv3

Same as

.Fl 3 .

.It rdirplus

Same as

.Fl l .

.It mntudp

Same as

.Fl U .

.It resvport

Same as

.Fl P .

.It seqpacket

Same as

.Fl p .

.It nqnfs

Same as

.Fl q .

.It soft

Same as

.Fl s .

.It tcp

Same as

.Fl T.

.El

.It Fl q

Use the leasing extensions to the NFS Version 3 protocol

to maintain cache consistency.

This protocol Version 2, referred to as Not Quite Nfs (NQNFS),

is only supported by this updated release of NFS code.

(It is not backwards compatible with the release of NQNFS that went out on

4.4BSD-Lite. To interoperate with a 4.4BSD-Lite NFS system you will have to

avoid this option until you have had an opportunity to upgrade the NFS code

on all your 4.4BSD-Lite based systems.)

.It Fl r

Set the read data size to the specified value.

It should normally be a power of 2 greater than or equal to 1024.

This should be used for UDP mounts when the

.Dq "fragments dropped due to timeout"

value is getting large while actively using a mount point.

(Use

.Xr netstat 1

with the

.Fl s

option to see what the

.Dq "fragments dropped due to timeout"

value is.)

See the

.Fl w

option as well.

.It Fl s

A soft mount, which implies that file system calls will fail

after \fBRetry\fR round trip timeout intervals.

.It Fl t

Set the initial retransmit timeout to the specified value.

May be useful for fine tuning UDP mounts over internetworks

with high packet loss rates or an overloaded server.

Try increasing the interval if

.Xr nfsstat 1

shows high retransmit rates while the file system is active or reducing the

value if there is a low retransmit rate but long response delay observed.

(Normally, the -d option should be specified when using this option to manually

tune the timeout

interval.)

.It Fl w

Set the write data size to the specified value.

Ditto the comments w.r.t. the

.Fl r

option, but using the

.Dq "fragments dropped due to timeout"

value on the server instead of the client.

Note that both the

.Fl r

and

.Fl w

options should only be used as a last ditch effort at improving performance

when mounting servers that do not support TCP mounts.

.It Fl x

Set the retransmit timeout count for soft mounts to the specified value.

.El

.Sh SEE ALSO

.Xr mount 2 ,

.Xr unmount 2 ,

.Xr fstab 5 ,

.Xr mount 8

.Sh BUGS

Due to the way that Sun RPC is implemented on top of UDP (unreliable datagram)

transport, tuning such mounts is really a black art that can only be expected

to have limited success.

For clients mounting servers that are not on the same

LAN cable or that tend to be overloaded,

TCP transport is strongly recommended,

but unfortunately this is restricted to mostly 4.4BSD servers.