4.4BSD/usr/src/sbin/mount_nfs/mount_nfs.8

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.\"	@(#)mount_nfs.8	8.1 (Berkeley) 6/5/93
.\"
.Dd June 5, 1993
.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 bsiTMlqdckPK
.Op Fl R Ar retrycnt
.Op Fl r Ar readsize
.Op Fl w Ar writesize
.Op Fl t Ar timeout
.Op Fl x Ar retrans
.Op Fl g Ar maxgroups
.Op Fl a Ar maxreadahead
.Op Fl L Ar leaseterm
.Op Fl D Ar deadthresh
.Op Fl m Ar realm
.Ar rhost:path node
.Sh DESCRIPTION
The
.Nm mount_nfs
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
setting the options with the
.Fl o
flag.
It implements the mount protocol as described in RFC 1094, Appendix A.
.Pp
The options are:
.Bl -tag -width indent
.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 s
A soft mount, which implies that file system calls will fail
after \fBRetry\fR round trip timeout intervals.
.It Fl i
An interruptible mount, 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 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 M
Assume that other clients are not writing a file concurrently with this client.
This implements a slightly less strict
consistency criteria than 4.3BSD Reno did,
that is more in line with most commercial client implementations.
This is recommended for servers that do not support leasing.
.It Fl d
Do not estimate retransmit timeout dynamically.
This may be useful for UDP
mounts that exhibit high retry rates.
.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
port number.
.It Fl P
Use a reserved socket port number. This is useful for mounting servers that
require clients to use a reserved port number.
.It Fl K
Pass Kerberos authenticators to the server for
client-to-server user-credential mapping.
This may only be used over TCP mounts between 4.4BSD clients and
servers.
.It Fl q
Use the leasing extensions to the protocol to maintain cache consistency.
This protocol, referred to as Not Quite Nfs (NQNFS),
is only supported by 4.4BSD servers.
.It Fl l
Used with NQNFS to specify that the
\fBReaddir_and_Lookup\fR RPC should be used.
This option reduces RPC traffic for cases such as ``ls -l'',
but increases the lease load on the server.
This is recommended unless the server is complaining
about excessive lease load.
.It Fl k
Used with NQNFS to specify ``get a lease'' for the file name being looked up.
This is recommended unless the server is complaining about excessive lease
load.
.El
.Pp
The following arguments take a value parameter that is either a decimal
number or a character string specified as =<value> after the option flag.
.Bl -tag -width indent
.It Fl R
Set the retry count for doing the mount to <value>.
.It Fl x
Set the retransmit timeout count for soft mounts to <value>.
.It Fl r
Set the read data size to <value>.
It should be a power of 2 greater than 512.
This should be used for UDP mounts when the
``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 ``fragments dropped due to timeout'' value is.)
.It Fl w
Set the write data size to <value>.
Ditto the comments w.r.t. the
.Fl r
option, but using the ``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 t
Set the initial retransmit timeout to <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.
.It Fl g
Set the maximum size of the group list for the credentials to <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 a
Set the read-ahead count to <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.
This is recommended for mounts with a large
bandwidth * delay product.
.It Fl L
Used with NQNFS to set the lease term to <value> seconds.
Only use this argument for mounts with a large round trip delay.
Values are normally in the 10-30 second range.
.It Fl D
Used with NQNFS to set the ``dead server threshold'' to <value> round trip
timeout intervals.
After a ``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 ``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 m
Set the Kerberos realm to the string argument. Used with the
.Fl K
option for mounts to other realms.
.El
.Sh SEE ALSO
.Xr mount 2 ,
.Xr unmount 2 ,
.Xr fstab 5
.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.