MOUNT_NFS(8) FreeBSD System Manager's Manual MOUNT_NFS(8)
NAME
mount_nfs - mount NFS file systems
SYNOPSIS
mount_nfs [-23bcdiLlNPsTU] [-a maxreadahead] [-D deadthresh]
[-g maxgroups] [-I readdirsize] [-o options] [-R retrycnt]
[-r readsize] [-t timeout] [-w writesize] [-x retrans]
rhost:path node
DESCRIPTION
The mount_nfs utility calls the nmount(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). For
NFSv2 and NFSv3, it implements the mount protocol as described in RFC
1094, Appendix A and RFC 1813, Appendix I. For NFSv4, it uses the NFSv4
protocol as described in RFC 7530, RFC 5661 and RFC 7862.
By default, mount_nfs keeps retrying until the mount succeeds. This
behaviour is intended for file systems listed in fstab(5) that are
critical to the boot process. For non-critical file systems, the bg and
retrycnt options 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. To modify this default
behaviour, see the intr and soft options.
The options are:
-o 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:
acregmin=<seconds>
acregmax=<seconds>
acdirmin=<seconds>
acdirmax=<seconds>
When attributes of files are cached, a timeout calculated
to determine whether a given cache entry has expired.
These four values determine the upper and lower bounds of
the timeouts for "directory" attributes and "regular"
(ie: everything else). The default values are 3 -> 60
seconds for regular files, and 30 -> 60 seconds for
directories. The algorithm to calculate the timeout is
based on the age of the file. The older the file, the
longer the cache is considered valid, subject to the
limits above.
actimeo=<seconds>
Set four cache timeouts above to specified value.
allgssname
This option can be used along with -o gssname to specify
that all operations should use the host-based initiator
credential. This may be used for clients that run system
daemons that need to access files on the NFSv4 mounted
volume.
bg 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 multiuser operation.
bgnow Like bg, fork off a child to keep trying the mount in the
background, but do not attempt to mount in the foreground
first. This eliminates a 60+ second timeout when the
server is not responding. Useful for speeding up the
boot process of a client when the server is likely to be
unavailable. This is often the case for interdependent
servers such as cross-mounted servers (each of two
servers is an NFS client of the other) and for cluster
nodes that must boot before the file servers.
deadthresh=<value>
Set the "dead server threshold" to the specified number
of round trip timeout intervals before a "server not
responding" message is displayed.
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.
fg Same as not specifying bg.
gssname=<service-principal-name>
This option can be used with the KerberosV security
flavors for NFSv4 mounts to specify the
"service-principal-name" of a host-based entry in the
default keytab file that is used for system operations.
It allows the mount to be performed by "root" and avoids
problems with cached credentials for the system
operations expiring. The "service-prinicpal-name" should
be specified without instance or domain and is typically
"host", "nfs" or "root", although the form
<service>@<fqdn> can also be used if the local system's
gethostname(3) value does not match the host-based
principal in the keytab.
hard Same as not specifying soft.
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.
maxgroups=<value>
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.
mntudp Force the mount protocol to use UDP transport, even for
TCP NFS mounts. (Necessary for some old BSD servers.)
nametimeo=<value>
Override the default of NFS_DEFAULT_NAMETIMEO for the
timeout (in seconds) for positive name cache entries. If
this is set to 0 it disables positive name caching for
the mount point.
negnametimeo=<value>
Override the default of NFS_DEFAULT_NEGNAMETIMEO for the
timeout (in seconds) for negative name cache entries. If
this is set to 0 it disables negative name caching for
the mount point.
nconnect=<value>
Specify the number of TCP connections (1-16) to be used
for an NFS Version 4, minor version 1 or 2 mount.
Multiple TCP connections can provide more client to
server network bandwidth for certain network
configurations such as:
- Multiple network interfaces that are aggregated together.
- A fast network interface that uses multiple queues.
The first TCP connection will be used for all RPCs that
consist entirely of small RPC messages. The RPCs that
can have large RPC messages (Read/Readdir/Write) are
distributed over the additional TCP connections in a
round robin fashion. This option will result in more IP
port#s being used. This option requires the nfsv4
option.
nfsv2 Use the NFS Version 2 protocol (the default is to try
version 3 first then version 2). Note that NFS version 2
has a file size limit of 2 gigabytes.
nfsv3 Use the NFS Version 3 protocol.
nfsv4 Use the NFS Version 4 protocol. This option will force
the mount to use TCP transport. By default, the highest
minor version of NFS Version 4 that is supported by the
NFS Version 4 server will be used. See the minorversion
option.
minorversion=<value>
Use the specified minor version for a NFS Version 4
mount, overriding the default. The minor versions
supported are 0, 1, and 2. This option is only
meaningful when used with the nfsv4 option.
oneopenown
Make a minor version 1 or 2 of the NFS Version 4 protocol
mount use a single OpenOwner for all Opens. This may be
useful for a server with a very low limit on OpenOwners,
such as AmazonEFS. It may be required when an
accumulation of NFS version 4 Opens occurs, as indicated
by the "Opens" count displayed by nfsstat(1) with the -c
and -E command-line options. A common case for an
accumulation of Opens is a shared library within the NFS
mount that is used by several processes, where at least
one of these processes is always running. This option
cannot be used for an NFS Version 4, minor version 0
mount. It may not work correctly when Delegations are
being issued by a server, but note that the AmazonEFS
server does not issued delegations at this time. This
option is only meaningful when used with the nfsv4
option.
pnfs Enable support for parallel NFS (pNFS) for minor version
1 or 2 of the NFS Version 4 protocol. This option is
only meaningful when used with the nfsv4 option.
noac Disable attribute caching.
noconn For UDP mount points, do not do a connect(2). This must
be used if the server does not reply to requests from the
standard NFS port number 2049 or replies to requests
using a different IP address (which can occur if the
server is multi-homed). Setting the
vfs.nfs.nfs_ip_paranoia sysctl to 0 will make this option
the default.
nocto Normally, NFS clients maintain the close-to-open cache
coherency. This works by flushing at close time and
checking at open time. Checking at open time is
implemented by getting attributes from the server and
purging the data cache if they do not match attributes
cached by the client.
This option disables checking at open time. It may
improve performance for read-only mounts, but should only
be used if the data on the server changes rarely. Be
sure to understand the consequences before enabling this
option.
noinet4, noinet6
Disables AF_INET or AF_INET6 connections. Useful for
hosts that have both an A record and an AAAA record for
the same name.
nolockd
Do not forward fcntl(2) locks over the wire via the NLM
protocol for NFSv3 mounts. All locks will be local and
not seen by the server and likewise not seen by other NFS
clients for NFSv3 mounts. This removes the need to run
the rpcbind(8) service and the rpc.statd(8) and
rpc.lockd(8) servers on the client. Note that this
option will only be honored when performing the initial
mount, it will be silently ignored if used while updating
the mount options. Also, note that NFSv4 mounts do not
use these daemons and handle locks over the wire in the
NFSv4 protocol. As such, this option is meaningless for
NFSv4 mounts.
noncontigwr
This mount option allows the NFS client to combine non-
contiguous byte ranges being written such that the dirty
byte range becomes a superset of the bytes that are
dirty. This reduces the number of writes significantly
for software builds. The merging of byte ranges is not
done if the file has been file locked, since most
applications modifying a file from multiple clients will
use file locking. As such, this option could result in a
corrupted file for the rare case of an application
modifying the file from multiple clients concurrently
without using file locking.
principal
For the RPCSEC_GSS security flavors, such as krb5, krb5i
and krb5p, this option sets the name of the host based
principal name expected by the server. This option
overrides the default, which will be ``nfs@<server-
fqdn>'' and should normally be sufficient.
noresvport
Do not use a reserved socket port number (see below).
port=<port_number>
Use specified port number for NFS requests. The default
is to query the portmapper for the NFS port.
proto=<protocol>
Specify transport protocol version to use. Currently,
they are:
udp - Use UDP over IPv4
tcp - Use TCP over IPv4
udp6 - Use UDP over IPv6
tcp6 - Use TCP over IPv6
rdirplus
Used with NFSV3 to specify that the ReaddirPlus RPC
should be used. For NFSV4, setting this option has a
similar effect, in that it will make the Readdir
Operation get more attributes. 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.
readahead=<value>
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.
readdirsize=<value>
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.
resvport
Use a reserved socket port number. This flag is
obsolete, and only retained for compatibility reasons.
Reserved port numbers are used by default now. (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.)
retrans=<value>
Set the retransmit timeout count for soft mounts to the
specified value.
retrycnt=<count>
Set the mount retry count to the specified value. The
default is a retry count of zero, which means to keep
retrying forever. There is a 60 second delay between
each attempt.
rsize=<value>
Set the read data size to the specified value. 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 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.)
sec=<flavor>
This option specifies what security flavor should be used
for the mount. Currently, they are:
krb5 - Use KerberosV authentication
krb5i - Use KerberosV authentication and
apply integrity checksums to RPCs
krb5p - Use KerberosV authentication and
encrypt the RPC data
sys - The default AUTH_SYS, which uses a
uid + gid list authenticator
soft A soft mount, which implies that file system calls will
fail after retrycnt round trip timeout intervals.
tcp Use TCP transport. This is the default option, as it
provides for increased reliability on both LAN and WAN
configurations compared to UDP. Some old NFS servers do
not support this method; UDP mounts may be required for
interoperability.
timeout=<value>
Set the initial retransmit timeout to the specified
value, expressed in tenths of a 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.)
timeo=<value>
Alias for timeout.
tls This option specifies that the connection to the server
must use TLS per RFC NNNN. TLS is only supported for TCP
connections and the rpc.tlsclntd(8) daemon must be
running for an NFS over TCP connection to use TLS.
tlscertname=<name>
This option specifies the name of an alternate
certificate to be presented to the NFS server during TLS
handshake. The default certificate file names are
"cert.pem" and "certkey.pem". When this option is
specified, name replaces "cert" in the above file names.
For example, if the value of name is specified as "other"
the certificate file names to be used will be "other.pem"
and "otherkey.pem". These files are stored in
/etc/rpc.tlsclntd by default. This option is only
meaningful when used with the tls option and the
rpc.tlsclntd(8) is running with the -m command line flag
set.
udp Use UDP transport.
vers=<vers_number>
Use the specified version number for NFS requests. See
the nfsv2, nfsv3, and nfsv4 options for details.
wcommitsize=<value>
Set the maximum pending write commit size to the
specified value. This determines the maximum amount of
pending write data that the NFS client is willing to
cache for each file.
wsize=<value>
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 the rsize and
wsize options should only be used as a last ditch effort
at improving performance when mounting servers that do
not support TCP mounts.
COMPATIBILITY
The following command line flags are equivalent to -o named options and
are supported for compatibility with older installations.
-2 Same as -o nfsv2
-3 Same as -o nfsv3
-D Same as -o deadthresh
-I Same as -o readdirsize=<value>
-L Same as -o nolockd
-N Same as -o noresvport
-P Use a reserved socket port number. This flag is obsolete, and
only retained for compatibility reasons. (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.)
-R Same as -o retrycnt=<value>
-T Same as -o tcp
-U Same as -o mntudp
-a Same as -o readahead=<value>
-b Same as -o bg
-c Same as -o noconn
-d Same as -o dumbtimer
-g Same as -o maxgroups
-i Same as -o intr
-l Same as -o rdirplus
-r Same as -o rsize=<value>
-s Same as -o soft
-t Same as -o retransmit=<value>
-w Same as -o wsize=<value>
-x Same as -o retrans=<value>
The following -o named options are equivalent to other -o named options
and are supported for compatibility with other operating systems (e.g.,
Linux, Solaris, and OSX) to ease usage of autofs(5) support.
-o vers=2
Same as -o nfsv2
-o vers=3
Same as -o nfsv3
-o vers=4
Same as -o nfsv4
IMPLEMENTATION NOTES
When neither the rsize nor wsize options are specified, the I/O size will
be set to the largest value supported by both the NFS client and server.
The largest value supported by the NFS client is defined by the tunable
vfs.maxbcachebuf which can be set to a power of two up to kern.maxphys.
The nfsstat(1) command with the -m command line option will show what
mount_nfs option settings are actually in use for the mount.
SEE ALSO
nfsstat(1), nmount(2), unmount(2), lagg(4), nfsv4(4), fstab(5), gssd(8),
mount(8), nfsd(8), nfsiod(8), rpc.tlsclntd(8), showmount(8)
HISTORY
A version of the mount_nfs utility appeared in 4.4BSD.
BUGS
Since nfsv4 performs open/lock operations that have their ordering
strictly enforced by the server, the options intr and soft cannot be
safely used. hard nfsv4 mounts are strongly recommended.
FreeBSD 13.1-RELEASE-p6 January 11, 2022 FreeBSD 13.1-RELEASE-p6
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