MOUNT_NFS(8) BSD System Manager's Manual MOUNT_NFS(8)NAME
mount_nfs — mount NFS file systems
mount_nfs [-23bcdiLlNPsTU] [-a maxreadahead] [-D deadthresh]
[-g maxgroups] [-I readdirsize] [-o options] [-R retrycnt]
[-r readsize] [-t timeout] [-w writesize] [-x retrans]
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). 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 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 be‐
haviour, see the intr and soft options.
The options are:
-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:
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 lim‐
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.
Set the “dead server threshold” to the specified number
of round trip timeout intervals before a “server not
responding” message is displayed.
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 esti‐
mated timeout interval is too short.
fg Same as not specifying bg.
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.
Set the maximum size of the group list for the creden‐
tials 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.)
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.
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 the experimental nfs subsystem and TCP
transport. To use the experimental nfs subsystem for
nfsv2 and nfsv3 mounts, you must specify the ``newnfs''
file system type instead of ``nfs''.
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
Disables AF_INET or AF_INET6 connections. Useful for
hosts that have both an A record and an AAAA record for
the same name.
Do not forward fcntl(2) locks over the wire. All locks
will be local and not seen by the server and likewise not
seen by other NFS clients. 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.
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 over‐
rides the default, which will be ``nfs@<server-fqdn>''
and should normally be sufficient.
Do not use a reserved socket port number (see below).
Use specified port number for NFS requests. The default
is to query the portmapper for the NFS port.
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 Opera‐
tion get more attributes. This option reduces RPC traf‐
fic 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 net‐
work interconnects with a large bandwidth times delay
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 prod‐
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.
Use a reserved socket port number. This flag is obso‐
lete, 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.)
Set the retransmit timeout count for soft mounts to the
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
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.)
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
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 over‐
loaded 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.)
udp Use UDP transport.
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.
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⟩
SEE ALSOnmount(2), unmount(2), nfsv4(4), fstab(5), gssd(8), mount(8), nfsd(8),
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.
BSD July 28, 2009 BSD