[-a maxreadahead] [-g maxgroups] [-m realm] [-o options]
[-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
point node. 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.
By default, mount_nfs keeps retrying until the mount succeeds. This be-
haviour is intended for file systems listed in fstab(5) that are critical
to the boot process. For non-critical file systems, the -b and -R flags
provide mechanisms to prevent the boot process from hanging if the server
is unavailable.
If the server becomes unresponsive while an NFS file system is mounted,
any new or outstanding file operations on that file system will hang
uninterruptibly until the server comes back (or that NFS file system is
forcibly unmounted). To modify this default behaviour, see the -i and -s
flags.
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.
-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.
-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
Authentication Mechanisms for ONC RPC, for more information.)
-L Do not support NFS file locking operations. Any attempt to per-
form file locking operations on this mount will return the error
ENOTSUP regardless of whether or not the NFS server supports NFS
file locking.
-P Use a reserved socket port number. 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 untrustwor-
thy users and the network cables are in secure areas this does
help, but for normal desktop clients this does not apply.)
tially. Trying larger values 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 file system mount is not critical to multi-
user operation.
-c For UDP mount points, do not do a connect(2). This must be used
for servers that do not reply to requests from the standard NFS
port number 2049. It may also be required for servers with more
than one IP address if replies come from an address other than
the one specified in the requests.
-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 a response
from the mount point.
-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 Used with NFSv3 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.
-m realm
Set the Kerberos realm to the string argument. Used with the -K
option for mounts to other realms. This requires that the kernel
be built with the NFSKERB option.
-o Options are specified with a -o flag followed by a comma sepa-
rated string of options. See the mount(8) man page for possible
options and their meanings. The following NFS-specific options
are also available:
bg The same as -b. Retry mount in background.
noconn The same as -c. Do not connect UDP sockets.
dumbtimer
rdirplus
The same as -l. Use the ReaddirPlus RPC with NFSv3
resvport
The same as -P. Use a reserved socket port number.
soft The same as -s. Make the mount soft. Fail file system
calls after a number of retries.
udp Use UDP transport. This is currently the default.
tcp The same as -T. Use TCP transport instead of UDP.
mntudp The same as -U. Force the mount protocol to use UDP
transport, even for TCP NFS mounts.
acregmin=<seconds>
acregmax=<seconds>
acdirmin=<seconds>
acdirmax=<seconds>
These options set the minimum and maximum attribute cache
timeouts for directories and "regular" (non-directory)
files. The default minimum is 5 seconds and the default
maximum is 60 seconds. Setting both the mininum and max-
imum to zero will disable attribute caching. The algo-
rithm to calculate the timeout is based on the age of the
file or directory. The older it is, the longer the
attribute cache is considered valid, subject to the lim-
its above.
actimeo=<seconds>
Set all minimum and maximum attribute cache timeouts to
the same value.
noac Disable attribute caching. This is equivalent to setting
actimeo to 0.
nolocks
nolockd
nolock
nonlm The same as -L. Do not support NFS file locking opera-
tions.
rsize=<readsize>
The same as -r. Set the read data size to the specified
timeo=<timeout>
The same as -t. Set the initial retransmit timeout.
retrans=<count>
The same as -x. Set the retransmit timeout count for
soft mounts.
-r readsize
Set the read data size to the specified value. The default is
8192 for UDP mounts and 16384 for TCP mounts. It should normally
be a power of 2 greater than or equal to 1024. Values greater
than 4096 should be multiples of 4096. It may need to be lowered
for UDP mounts when the ``fragments dropped due to timeout''
value is getting large while actively using a mount point. (Use
netstat(1) with the -s option to see what the ``fragments dropped
due to timeout'' value is.) See the -w option as well.
-s A soft mount, which implies that file system calls will fail
after Retry round trip timeout intervals.
-t timeout
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 nfsstat(1) shows high retransmit rates while the file
system is active or reducing the value if there is a low retrans-
mit rate but long response delay observed. (Normally, the -d
option should be specified when using this option to manually
tune the timeout interval.)
-w writesize
Set the write data size to the specified value. Ditto the com-
ments w.r.t. the -r option, but using the ``fragments dropped due
to timeout'' value on the 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 retrans
Set the retransmit timeout count for soft mounts to the specified
value.
EXAMPLES
The simplest way to invoke mount_nfs is with a command like:
mount remotehost:/filesystem /localmountpoint
or:
mount -t nfs remotehost:/filesystem /localmountpoint
It is also possible to automatically mount file systems at boot from your
/etc/fstab by using a line like:
Any value over 32K is unlikely to get you more performance,
unless you have a very fast network.
o 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 lossy network connections (e.g.
wireless networks) which can lead 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.
o For connections that are not on the same LAN, and/or may experi-
ence 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 file
system you requested or is not exporting it to your host. If you believe
the remote host is indeed exporting a file system to you, make sure the
exports(5) file is exporting the proper directories. The program
showmount(8) can be used to see a server's exports list. The command
``showmount -e remotehostname'' will display what file systems the remote
host is exporting.
A common mistake is that mountd(8) will not export a file system 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, mountd, rpc.statd, and rpc.lockd it
would display:
program vers proto port
100000 2 tcp 111 portmapper
100000 2 udp 111 portmapper
100021 0 tcp 917 nlockmgr
100021 1 tcp 917 nlockmgr
100021 3 tcp 917 nlockmgr
100021 4 tcp 917 nlockmgr
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
mount(2), unmount(2), fstab(5), mount(8,) umount(8,) nfsstat(1),
netstat(1), rpcinfo(8), showmount(8), automount(8)
CAVEATS
An NFS server shouldn't loopback-mount its own exported file systems
because it's fundamentally prone to deadlock.
BSD February 8, 2005 BSD
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