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
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 need 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/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)
CAVEATS
An NFS server shouldn't loopback-mount its own exported file systems because
it's fundamentally prone to deadlock.