NAME
mount_nfs —
mount NFS file
systems
SYNOPSIS
mount_nfs |
[-23bCcdilPpqsTUX]
[-a
maxreadahead]
[-D
deadthresh]
[-g
maxgroups]
[-I
readdirsize]
[-L
leaseterm]
[-o
options]
[-R
retrycnt]
[-r
readsize]
[-t
timeout]
[-w
writesize]
[-x
retrans] rhost:path
node |
DESCRIPTION
The
mount_nfs command calls the
mount(2) system call to prepare
and graft a remote NFS file system (rhost:path) on to the file system tree at
the mount point
node. The directory specified by
node is converted to an absolute path before use. This
command is normally executed by
mount(8). It implements the mount
protocol as described in RFC 1094, Appendix A and
NFS:
Network File System Version 3 Protocol Specification, Appendix I.
The options are:
-
-
- -2
- Use the NFS Version 2 protocol.
-
-
- -3
- Use the NFS Version 3 protocol. The default is to try
version 3 first, and fall back to version 2 if the mount fails.
-
-
- -a
maxreadahead
- 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.
-
-
- -b
- If an initial attempt to contact the server fails, fork off
a child to keep trying the mount in the background. Useful for
fstab(5), where the
filesystem mount is not critical to multiuser operation.
-
-
- -C
- For UDP mount points, do a
connect(2). Although this
flag increases the efficiency of UDP mounts it cannot be used for servers
that do not reply to requests from the standard NFS port number 2049, or
for servers with multiple network interfaces. In these cases if the socket
is connected and the server replies from a different port number or a
different network interface the client will get ICMP port unreachable and
the mount will hang.
-
-
- -c
- For UDP mount points, do not do a
connect(2). This flag is
deprecated and connectionless UDP mounts are the default.
-
-
- -D
deadthresh
- Set the “dead server threshold” to the
specified number of round trip timeout intervals. After a “dead
server threshold” of retransmit timeouts, “not
responding” message is printed to a tty.
-
-
- -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.
-
-
- -g
maxgroups
- 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.
-
-
- -I
readdirsize
- 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.
-
-
- -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.
-
-
- -L
leaseterm
- Ignored. It used to be NQNFS lease term.
-
-
- -l
- Used with NFS Version 3 to specify that the
ReaddirPlus() RPC should be used. This option reduces
RPC traffic for cases such as 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.
-
-
- -o
options
- Options are specified with a -o flag
followed by a comma separated string of options. See the
mount(8) man page for
possible options and their meanings.
The following NFS specific options are also available:
-
-
- bg
- Same as -b.
-
-
- conn
- Same as -C.
-
-
- deadthresh=⟨deadthresh⟩
- Same as -D
deadthresh.
-
-
- dumbtimer
- Same as -d.
-
-
- intr
- Same as -i.
-
-
- leaseterm=⟨leaseterm⟩
- Same as -L
leaseterm.
-
-
- maxgrps=⟨maxgroups⟩
- Same as -g
maxgroups.
-
-
- mntudp
- Same as -U.
-
-
- nfsv2
- Same as -2.
-
-
- nfsv3
- Same as -3.
-
-
- noresport
- Same as -p.
-
-
- nqnfs
- Same as -q.
-
-
- port=⟨portnumber⟩
- Use the specified port number for NFS requests. The
default is to query the portmapper for the NFS port.
-
-
- rdirplus
- Same as -l.
-
-
- readahead=⟨maxreadahead⟩
- Same as -a
maxreadahead.
-
-
- rsize=⟨readsize⟩
- Same as --r
readsize.
-
-
- soft
- Same as -s.
-
-
- tcp
- Same as -T.
-
-
- timeo=⟨timeout⟩
- Same as -t
timeout.
-
-
- wsize=⟨writesize⟩
- Same as -w
writesize.
-
-
- -P
- Use a reserved socket port number. This is the default, and
available for backwards compatibility purposes only.
-
-
- -p
- Do not use a reserved port number for RPCs. This option is
provided only to be able to mimic the old default behavior of not using a
reserved port, and should rarely be useful.
-
-
- -q
- A synonym of -3. It used to specify
NQNFS.
-
-
- -R
retrycnt
- Set the retry count for doing the mount to the specified
value. The default is 10000.
-
-
- -r
readsize
- Set the read data size to the specified value in bytes. It
should normally be a power of 2 greater than or equal to 1024.
This should be used for UDP mounts when the “fragments dropped after
timeout” value is getting large while actively using a mount point.
Use netstat(1) with the
-s option to see what the “fragments dropped after
timeout” value is. See the mount_nfs
-w option also.
-
-
- -s
- A soft mount, which implies that file system calls will
fail after retrans round trip timeout
intervals.
-
-
- -T
- Use TCP transport instead of UDP. This is recommended for
servers that are not on the same physical network as the client. Not all
NFS servers, especially not old ones, support this.
-
-
- -t
timeout
- Set the initial retransmit timeout to the specified value
in 0.1 seconds. May be useful for fine tuning UDP mounts over
internetworks with high packet loss rates or an overloaded server. Try
increasing the interval if
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. The default is 3 seconds.
-
-
- -U
- Force the mount protocol to use UDP transport, even for TCP
NFS mounts. This is necessary for some old BSD
servers.
-
-
- -w
writesize
- Set the write data size to the specified value in bytes.
The same logic applies for use of this option as with the
mount_nfs -r option, but using the
“fragments dropped after timeout” value on the NFS server
instead of the client. Note that both the -r and
-w options should only be used as a last ditch effort at
improving performance when mounting servers that do not support TCP
mounts.
-
-
- -X
- Perform 32 <-> 64 bit directory cookie translation
for version 3 mounts. This may be needed in the case of a server using the
upper 32 bits of version 3 directory cookies, and when you are running
emulated binaries that access such a filesystem. Native
NetBSD binaries will never need this option. This
option introduces some overhead.
-
-
- -x
retrans
- Set the retransmit timeout count for soft mounts to the
specified value. The default is 10.
EXAMPLES
The simplest way to invoke
mount_nfs is with a command like:
mount -t nfs remotehost:/filesystem
/localmountpoint
It is also possible to automatically mount filesystems at boot from your
/etc/fstab by using a line like:
remotehost:/home /home nfs rw 0 0
As can be derived from the comments accompanying the options, performance tuning
of NFS can be a non-trivial task. Here are some common points to watch:
- Increasing the read and write size with the
-r and -w options respectively will
increase throughput if the network interface can handle the larger packet
sizes.
The default size for NFS version 2 is 8K when using UDP, 64K when using TCP.
The default size for NFS version 3 is platform dependent: on
NetBSD/amd64 and
NetBSD/i386, the default is 32K, for other
platforms it is 8K. Values over 32K are only supported for TCP, where 64K
is the maximum.
Any value over 32K is unlikely to get you more performance, unless you have
a very fast network.
- If the network interface cannot handle larger packet
sizes or a long train of back to back packets, you may see low performance
figures or even temporary hangups during NFS activity.
This can especially happen with older Ethernet network interfaces. What
happens is that either the receive buffer on the network interface on the
client side is overflowing, or that similar events occur on the server,
leading to a lot of dropped packets.
In this case, decreasing the read and write size, using TCP, or a
combination of both will usually lead to better throughput. Should you
need to decrease the read and write size for all your NFS mounts because
of a slow Ethernet network interface (e.g. a USB 1.1 to 10/100 Ethernet
network interface), you can use
- options
NFS_RSIZE=value
- options
NFS_WSIZE=value
in your kernel config(1) file
to avoid having do specify the sizes for all mounts.
- For connections that are not on the same LAN, and/or may
experience packet loss, using TCP is strongly recommended.
ERRORS
Some common problems with
mount_nfs can be difficult for first
time users to understand.
mount_nfs: can't access /foo: Permission
denied
This message means that the remote host is either not exporting the filesystem
you requested, or is not exporting it to your host. If you believe the remote
host is indeed exporting a filesystem to you, make sure the
exports(5) file is exporting
the proper directories.
A common mistake is that
mountd(8)
will not export a filesystem with the
-alldirs option,
unless it is a mount point on the exporting host. It is not possible to
remotely mount a subdirectory of an exported mount, unless it is exported with
the
-alldirs option.
The following error:
NFS Portmap: RPC: Program not
registered
means that the remote host is not running
mountd(8). The program
rpcinfo(8) can be used to
determine if the remote host is running nfsd, and mountd by issuing the
command:
rpcinfo -p remotehostname
If the remote host is running nfsd, and mountd, it would display:
100005 3 udp 719 mountd
100005 1 tcp 720 mountd
100005 3 tcp 720 mountd
100003 2 udp 2049 nfs
100003 3 udp 2049 nfs
100003 2 tcp 2049 nfs
100003 3 tcp 2049 nfs
The error:
mount_nfs: can't get net id for
host
indicates that
mount_nfs cannot resolve the name of the remote
host.
SEE ALSO
nfsstat(1),
mount(2),
unmount(2),
options(4),
exports(5),
fstab(5),
mount(8),
mountd(8),
rpcinfo(8)
NFS: Network File System Protocol
specification, RFC 1094,
March 1989.
NFS Version 2 and Version 3 Security Issues
and the NFS Protocol's Use of RPCSEC_GCC and Kerberos V5,
RFC 2623, June 1999.
NFS Version 4 Design Considerations,
RFC 2624, June 1999.
Authentication Mechanisms for ONC RPC,
RFC 2695, September
1999.
HISTORY
A version of the
mount_nfs utility appeared in
4.4BSD.
CAVEATS
An NFS server should not mount its own exported file systems (loopback fashion)
because doing so is fundamentally prone to deadlock.