NAME
mount_nfs
—
mount NFS file systems
SYNOPSIS
mount_nfs |
[-o options]
server:/path directory |
DESCRIPTION
The mount_nfs
command calls the
mount(2)
system call to prepare and graft a remote NFS file system (
server:/path ) on to the file system tree at the point
directory.
This command is expected to be executed by the
mount(8)
command. Direct use of mount_nfs
to mount NFS file
systems is strongly discouraged because there is little practical benefit of
using it instead of mount(8).
For NFS versions that use a separate mount protocol,
mount_nfs
implements the mount protocol as described
in RFC 1094, Appendix A and NFS: Network File System
Version 3 Protocol Specification, RFC 1813, Appendix I.
By default, mount_nfs
will attempt the
mount twice before exiting with an error. If the -o
bg
option is given, it will attempt the mount once
and then background itself to continue trying another 10,000 times (pausing
for one minute between attempts). The option -o
retrycnt
=⟨num⟩
can be used if a different retry behavior is desired for a mount.
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
-o
intr
and
-o
soft
mount options.
Mount 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
- Retry mount in background. If an initial attempt to contact the server fails, fork off a child to keep trying the mount in the background. Useful for startup scripts where the file system mount is not critical to multiuser operation.
retrycnt
=⟨num⟩- Set the retry count for doing the mount to the specified value. The
default is 1 for foreground mounts and 10,000 for background mounts.
Setting
retrycnt
to 0, in addition to only trying to establish connection once, will case nfs client code to use quick time out value (default 8s) instead of regular mount time out (default 30s) value while establishing initial connection. udp
- Use UDP transport protocol.
tcp
- Use the TCP transport protocol instead of UDP. The default is to try TCP first, then fall back to UDP if the server doesn't support TCP.
inet
- Use only IPv4 addresses.
inet6
- Use only IPv6 addresses.
proto
=⟨netid⟩- Use the transport protocol and address family as specified by the given
ONC RPC Netid (RFC 5665). Valid netid values are:
tcp
(TCP over IPv4),udp
(UDP over IPv4),tcp6
(TCP over IPv6), andudp6
(UDP over IPv6). Note that this option differs from the separatetcp
andudp
options described above in that each netid value specifies both a transport protocol and address family (IP version). mntudp
- Force the mount protocol to use UDP transport, even for TCP NFS mounts. (Necessary for some old BSD servers.)
mountport
=⟨port-number⟩- Connect to the NFS server's mount daemon using the given port number.
port
=⟨port-number⟩- Connect to an NFS server at the given port number.
noconn
- Do not connect UDP sockets. 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.
resvport
- 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 untrustworthy users and the network cables are in
secure areas this does help, but for normal desktop clients this does not
apply.) root permission is required to mount using
resvport
mount option. intr
- 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. soft
- Make the mount soft, which means that file system calls will fail after
retrans
round trip timeout intervals. Note: mounts which are both soft and read-only will also have thelocallocks
mount option enabled by default - unless explicitly overridden with a lock option (for example,nolocks
ornolocallocks
). vers
=⟨num[.num]⟩[-
⟨num[.num]⟩]nfsvers
=⟨num[.num]⟩[-
⟨num[.num]⟩]- NFS protocol version number - 2 for NFSv2, 3 for NFSv3 and 4 for NFSv4.
The default is to try version 3 first, and fall back to version 2 if the
mount fails. A range of versions can be specified by including a dash and
another version with no spaces between versions and the dash. In that case
the highest version is tried first and if not successful fall back to each
version down to the lowest version specified until the mount succeeds or
the lowest version fails. Note minor versions may be specified for
versions greater than or equal to four by appending a dot and then the
minor version number. Currently NFSv4 is the highest supported version
with a minor version of zero. If no minor version is specified, zero is
assumed. Specifying a non supported version or minor version will print a
warning and ignore the
vers
ornfsvers
option. Versions 2 or 3 do not support minor versioning so minor versions greater than zero are treated as above. nfsv2
nfsv3
nfsv4
- Deprecated. Use
-o
vers
=⟨num⟩ to specify NFS protocol version. sec
=⟨mechanism⟩- Force a specific security mechanism to be used for the mount, where mechanism is one of: krb5p, krb5i, krb5, or sys. When this option is not given the security mechanism will be negotiated transparently with the remote server.
etype
=⟨encryption-type⟩- Use the specified encryption type for the mount, where encryption-type is one of: des3, des3-cbc-sha1, des3-cbc-sha1-kd, aes128, aes128-cts-hmac-sha1, aes128-cts-hmac-sha1-96, aes256-cts-hmac-sha1, or aes256-cts-hmac-sha1-96.
realm
=⟨realm⟩- Use the default credential for realm or security domain. For Kerberos realms are usually uppercase. If the realm specified does not begin with an “@”, an “@” sign will be prepended to it. Note specifying the realm is typically used for automounter maps when clients may have multiple credential caches, and tells the client what cache to use on the mount.
principal
=⟨principal⟩- Use the specified principal for acquiring credentials for the mount. That principal will be used for all accesses by the mounting credential on the mounted file system. Note specifying a principal is useful for user initiated command line mounts, where the user knows the particular credential to use.
sprincipal
=⟨server-principal⟩- Use the specified server-principal for establishing credentials for the mount. That server principal will be use for all mount access. If no server principal is specified, then the GSS_C_NT_HOSTBASED_SERVICE nfs@server is used, where server is taken from the mount argument server:/path. Note its rare to use this option.
rsize
=⟨readsize⟩- Set the read data size to the specified value. The default is 8192 for UDP
mounts and 32768 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.) wsize
=⟨writesize⟩- Set the write data size to the specified value. Ditto the comments w.r.t.
the
rsize
option, but using the “fragments dropped due to timeout” value on the server instead of the client. Note that both thersize
andwsize
options should only be used as a last ditch effort at improving performance when mounting servers that do not support TCP mounts. rwsize
=⟨size⟩- Set both the read data size and write data size to the specified value.
dsize
=⟨readdirsize⟩- Set the directory read size to the specified value. The value should normally be a multiple of DIRBLKSIZ that is <= the read size for the mount. The default is 8192 for UDP mounts and 32768 for TCP mounts.
readahead
=⟨maxreadahead⟩- Set the maximum read-ahead count to the specified value. The default is 16. This may be in the range of 0 - 128, and determines how many Read RPCs will be read ahead when a large file is being read sequentially. Trying larger values for this is suggested for mounts with a large bandwidth * delay product.
rdirplus / nordirplus
- Used with NFS v3/v4 to specify that directory read operations should retrieve additional information about each entry (e.g. use the NFSv3 ReaddirPlus RPC). This option typically reduces RPC traffic for cases such as directory listings that use or display basic attributes (e.g. “ls -F” and “find . -type f” ). Note that the long directory listing format case (i.e. “ls -l” ) may not be helped much when the file system does not natively support extended attributes. Older implementations tended to flood the vnode and name caches with prefetched entries which may not be referenced. The current implementation avoids creating those entries until they are referenced. 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. Default value is rdirplus.
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 minimum and maximum to zero will disable attribute caching. The algorithm 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 limits above. Note that the effectiveness of this algorithm depends on how well the clocks on the client and server are synchronized.
actimeo
=⟨seconds⟩- Set all attribute cache timeouts to the same value.
noac
- Disable attribute caching. Equivalent to setting
actimeo
to 0. nonegnamecache
- Disable negative name caching.
locallocks
- For NFSv2/v3 mounts, perform all file locking operations locally on the
NFS client (in the VFS layer) instead of on the NFS server. This option
can provide file locking support on an NFS file system for which the
server does not support file locking. However, because the file locking is
only performed on the client, the NFS server and other NFS clients will
have no knowledge of the locks. Note: mounts which are both soft and
read-only will also have the
locallocks
mount option enabled by default - unless explicitly overridden with a lock option (for example,nolocks
ornolocallocks
). nolocks
nolockd
nolock
nonlm
- For NFSv2/v3 mounts, do not support NFS file locking operations. Any
attempt to perform file locking operations on this mount will return the
error
ENOTSUP
regardless of whether or not the NFS server supports NFS file locking. noquota
- Do not support file system quota operations that would normally be
serviced by using the RQUOTA protocol. Any attempt to perform quota
operations on this mount will return the error
ENOTSUP
regardless of whether or not the NFS server supports the RQUOTA service. maxgroups
=⟨num⟩- 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.
dumbtimer
- 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.
timeo
=⟨timeout⟩- Set the initial retransmit timeout to the specified value (in tenths of a
second). The default is 1 second. 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
dumbtimer
option should be specified when using this option to manually tune the timeout interval.) retrans
=⟨count⟩- Set the retransmit timeout count for soft mounts to the specified value. The default value is 10.
deadtimeout
=⟨timeout⟩- If the mount is still unresponsive timeout seconds
after it is initially reported unresponsive, then mark the mount as dead
so that it will be forcibly unmounted. Note: mounts which are both soft
and read-only will also have the
deadtimeout
mount option set to 60 seconds. This can be explicitly overridden by settingdeadtimeout
=0. mutejukebox
- When NFS requests repeatedly get jukebox errors (NFS3ERR_JUKEBOX, NFS4ERR_DELAY) from the server the NFS file system is reported as being unresponsive. Use of this option will prevent the file system from being included in the list of unresponsive file systems that would be included in a dialog presented to the user. This option may be useful when a file system is expected to get such errors during normal operation. For example, when it's backed by a hierarchical storage management system.
async
- Assume that unstable write requests have actually been committed to stable
storage on the server, and thus will not require resending in the event
that the server crashes. Use of this option may improve performance but
only at the risk of data loss if the server crashes. Note: this mount
option will only be honored if the
nfs.client.allow_async
option in nfs.conf(5) is also enabled. sync
- Perform I/O requests (specifically, write requests) synchronously. The
operation will not return until a response is received from the server.
(The default,
nosync
, behavior is to return once the I/O has been queued up.) nocallback
- For NFSv4 mounts, don't support callback requests from the server. This should effectively disable features that require callback requests such as delegations.
nonamedattr
- For NFSv4 mounts, don't support named attributes even if the server does. This is the default.
namedattr
- For NFSv4 mounts, if the server appears to support named attributes, they will be used to store extended attributes and named streams (e.g. FinderInfo and resource forks).
noacl
- For NFSv4 mounts, don't support ACLs even if the server does. ACLs are
currently disabled by default to avoid issues with the way ACLs and modes
are handled differently on other operating systems. This may be overriden
by specifying the
acl
option. aclonly
- For NFSv4 mounts, only support ACLs; do not support the mode attribute.
(Any mode attribute values returned will have all permission bits set -
regardless of the value of any ACL or access mode stored in the file
system.) This option overrides the
noacl
option. nfc
- Convert name strings to Unicode Normalization Form C (NFC) when sending them to the NFS server. This option may be used to improve interoperability with NFS clients and servers that typically use names in the NFC form.
nfs.conf(5) can be used to configure some NFS client options. In
particular, nfs.client.mount.options
can be used to
specify default mount options. This can be useful in situations where it is
not easy to configure the command-line options. Some NFS client options in
nfs.conf(5) correspond to kernel configuration values which will get
set by mount_nfs
when performing a mount. To update
these values without performing a mount, use the command:
mount_nfs
configupdate
.
COMPATIBILITY
The following mount_nfs
command line flags
have equivalent -o
option
forms (shown in parentheses) and their use is strongly discouraged. These
command line flags are deprecated and the -o
option forms should be used instead.
-2
(vers=2), -3
(vers=3), -4
(vers=4), -L
(nolocks), -P
(resvport), -T
(tcp), -U
(mntudp), -b
(bg),
-c
(noconn), -d
(dumbtimer),
-i
(intr), -l
(rdirplus),
-m
(nordirplus), -s
(soft),
-I
readdirsize (dsize=#),
-R
retrycnt (retrycnt=#),
-a
maxreadahead (readahead=#),
-g
maxgroups (maxgroups=#),
-r
readsize (rsize=#),
-t
timeout (timeo=#),
-w
writesize (wsize=#),
-x
retrans (retrans=#).
EXAMPLES
The simplest way to invoke mount_nfs
is
with a command like:
mount remotehost:/filesystem
/localmountpoint
or:
mount -t nfs remotehost:/filesystem
/localmountpoint
PERFORMANCE
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:
- Use of the
sync
option will probably have a detrimental affect on performance. Its use is discouraged as it provides little benefit. - Use of the
async
option may improve performance, but only at the risk of losing data if the server crashes because the client will not be making sure that all data is committed to stable storage on the server. - Increasing the read and write size with the
rsize
andwsize
options respectively will increase throughput if the network interface can handle the larger packet sizes.The default read and write sizes are 8K when using UDP, and 32K when using TCP. Values over 16K are only supported for TCP, where 2M 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 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.
- 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 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 nfsd(8). or 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
100005 1 udp 950 mountd
100005 3 udp 950 mountd
100005 1 tcp 884 mountd
100005 3 tcp 884 mountd
100003 2 udp 2049 nfs
100003 3 udp 2049 nfs
100003 2 tcp 2049 nfs
100003 3 tcp 2049 nfs
100024 1 udp 644 status
100024 1 tcp 918 status
100021 0 udp 630
nlockmgr
100021 1 udp 630
nlockmgr
100021 3 udp 630
nlockmgr
100021 4 udp 630
nlockmgr
100021 0 tcp 917
nlockmgr
100021 1 tcp 917
nlockmgr
100021 3 tcp 917
nlockmgr
100021 4 tcp 917
nlockmgr
The following error:
mount_nfs: can't resolve
host
indicates that mount_nfs
could not resolve
the name of the remote host.
The following error:
In case the remote host is not running rpc.statd and the client is
mounting the NFS directory with remote locks (enabled by default),
mount_nfs
should fail with EPROGUNAVAIL. rpc.statd
status can be verified using rpcinfo (see above).
The following warning:
indicates that provided wsize
is much
greater than rsize.
which could end up with a
different amount of readahead
RPCs compared to the
amount requested by the user.
SEE ALSO
mount(2), unmount(2), mount(8), umount(8), nfsstat(1), netstat(1), rpcinfo(8), showmount(8), automount(8), nfs.conf(5), nfs(5)
CAVEATS
An NFS server shouldn't loopback-mount its own exported file systems because it's fundamentally prone to deadlock.