Name
mount_nfs - mount remote NFS resources
Synopsis
mount [-F nfs] [generic_options] [-o specific_options] [-O] resource
mount [-F nfs] [generic_options] [-o specific_options] [-O] mount_point
mount [-F nfs] [generic_options] [-o specific_options]
[-O] resource mount_point
Description
The mount utility attaches a named resource to the file sys-
tem hierarchy at the pathname location mount_point, which
must already exist. If mount_point has any contents prior to
the mount operation, the contents remain hidden until the
resource is once again unmounted.
mount_nfs starts the lockd(1M) and statd(1M) daemons if they
are not already running.
If the resource is listed in the /etc/vfstab file, the com-
mand line can specify either resource or mount_point, and
mount consults /etc/vfstab for more information. If the -F
option is omitted, mount takes the file system type from
/etc/vfstab.
If the resource is not listed in the /etc/vfstab file, then
the command line must specify both the resource and the
mount_point.
host can be an IPv4 or IPv6 address string. As IPv6
addresses already contain colons, enclose host in a pair of
square brackets when specifying an IPv6 address string. Oth-
erwise the first occurrence of a colon can be interpreted as
the separator between the host name and path, for example,
[1080::8:800:200C:417A]:tmp/file. See inet(7P) and
inet6(7P).
host:pathname
Where host is the name of the NFS server host, and path-
name is the path name of the directory on the server
being mounted. The path name is interpreted according to
the server's path name parsing rules and is not neces-
sarily slash-separated, though on most servers, this is
the case.
nfs://host[:port]/pathname
This is an NFS URL and follows the standard convention
for NFS URLs as described in NFS URL Scheme, RFC 2224.
See the discussion of URL's and the public option under
NFS FILE SYSTEMS for a more detailed discussion.
host:pathname nfs://host[:port]/pathname
host:pathname is a comma-separated list of
host:pathname.
See the discussion of replicated file systems and fail-
over under NFS FILE SYSTEMS for a more detailed discus-
sion.
hostlist pathname
hostlist is a comma-separated list of hosts.
See the discussion of replicated file systems and fail-
over under NFS FILE SYSTEMS for a more detailed discus-
sion.
The mount command maintains a table of mounted file systems
in /etc/mnttab, described in mnttab(4).
mount_nfs supports both NFSv3 and NFSv4 mounts. The default
NFS version is NFSv4.
SMF Management
The NFS client service is managed by the service management
facility, smf(5), under the service identifier:
svc:/network/nfs/client:default
Administrative actions on this service, such as enabling,
disabling, or requesting restart, can be performed using
svcadm(1M). The service's status can be queried using the
svcs(1) command.
Options
See mount(1M) for the list of supported generic_options. See
share_nfs(1M) for a description of server options.
-o specific_options
Set file system specific options according to a comma-
separated list with no intervening spaces.
acdirmax=n
Hold cached attributes for no more than n seconds
after directory update. The default value is 60.
acdirmin=n
Hold cached attributes for at least n seconds after
directory update. The default value is 30.
acregmax=n
Hold cached attributes for no more than n seconds
after file modification. The default value is 60.
acregmin=n
Hold cached attributes for at least n seconds after
file modification. The default value is 3.
actimeo=n
Set min and max times for regular files and direc-
tories to n seconds. See "File Attributes," below,
for a description of the effect of setting this
option to 0.
See "Specifying Values for Attribute Cache Duration
Options," below, for a description of how acdirmax,
acdirmin, acregmax, acregmin, and actimeo are parsed
on a mount command line.
bg | fg
If the first attempt fails, retry in the background,
or, in the foreground. The default is fg.
forcedirectio | noforcedirectio
If forcedirectio is specified, then for the duration
of the mount, forced direct I/O is used. If the
filesystem is mounted using forcedirectio, data is
transferred directly between client and server, with
no buffering on the client. If the filesystem is
mounted using noforcedirectio, data is buffered on
the client. forcedirectio is a performance option
that is of benefit only in large sequential data
transfers. The default behavior is noforcedirectio.
grpid
By default, the GID associated with a newly created
file obeys the System V semantics; that is, the GID
is set to the effective GID of the calling process.
This behavior can be overridden on a per-directory
basis by setting the set-GID bit of the parent
directory; in this case, the GID of a newly created
file is set to the GID of the parent directory (see
open(2) and mkdir(2)). Files created on file systems
that are mounted with the grpid option obeys BSD
semantics independent of whether the set-GID bit of
the parent directory is set; that is, the GID is
unconditionally inherited from that of the parent
directory.
hard | soft
Continue to retry requests until the server responds
(hard) or give up and return an error (soft). The
default value is hard. Note that NFSv4 clients do
not support soft mounts.
intr | nointr
Allow (do not allow) keyboard interrupts to kill a
process that is hung while waiting for a response on
a hard-mounted file system. The default is intr,
which makes it possible for clients to interrupt
applications that can be waiting for a remote mount.
llock
Use local locking (no lock manager). Note that this
is a private interface.
noac
Suppress data and attribute caching. The data cach-
ing that is suppressed is the write-behind. The
local page cache is still maintained, but data
copied into it is immediately written to the server.
nocto
Do not perform the normal close-to-open consistency.
When a file is closed, all modified data associated
with the file is flushed to the server and not held
on the client. When a file is opened the client
sends a request to the server to validate the
client's local caches. This behavior ensures a
file's consistency across multiple NFS clients. When
nocto is in effect, the client does not perform the
flush on close and the request for validation,
allowing the possiblity of differences among copies
of the same file as stored on multiple clients.
This option can be used where it can be guaranteed
that accesses to a specified file system are made
from only one client and only that client. Under
such a condition, the effect of nocto can be a
slight performance gain.
port=n
The server IP port number. The default is NFS_PORT.
If the port option is specified, and if the resource
includes one or more NFS URLs, and if any of the
URLs include a port number, then the port number in
the option and in the URL must be the same.
posix
Request POSIX.1 semantics for the file system.
Requires a mount version 2 mountd(1M) on the server.
See standards(5) for information regarding POSIX.
proto=netid | rdma
By default, the transport protocol that the NFS
mount uses is the first available RDMA transport
supported both by the client and the server. If no
RDMA transport is found, then it attempts to use a
TCP transport or, failing that, a UDP transport, as
ordered in the /etc/netconfig file. If it does not
find a connection oriented transport, it uses the
first available connectionless transport.
Use this option to override the default behavior.
proto is set to the value of netid or rdma. netid is
the value of the network_id field entry in the
/etc/netconfig file.
The UDP protocol is not supported for NFS version 4.
If you specify a UDP protocol with the proto option,
NFS version 4 is not used.
public
The public option forces the use of the public file
handle when connecting to the NFS server. The
resource specified might not have an NFS URL. See
the discussion of URLs and the public option under
NFS FILE SYSTEMS for a more detailed discussion.
quota | noquota
Enable or prevent quota(1M) to check whether the
user is over quota on this file system; if the file
system has quotas enabled on the server, quotas are
still checked for operations on this file system.
remount
Remounts a read-only file system as read-write
(using the rw option). This option cannot be used
with other -o options, and this option works only on
currently mounted read-only file systems.
retrans=n
Set the number of NFS retransmissions to n. The
default value is 5. For connection-oriented tran-
sports, this option has no effect because it is
assumed that the transport performs retransmissions
on behalf of NFS.
retry=n
The number of times to retry the mount operation.
The default for the mount command is 10000.
The default for the automounter is 0, in other
words, do not retry. You might find it useful to
increase this value on heavily loaded servers, where
automounter traffic is dropped, causing unnecessary
server not responding errors.
rsize=n
Set the read buffer size to a maximum of n bytes.
The default value is 1048576 when using connection-
orientated transports with version 3 or version 4 of
the NFS protocol, and 32768 when using connection-
less transports. The default can be negotiated down
if the server prefers a smaller transfer size.
"Read" operations may not necessarily use the max-
imum buffer size. When using version 2, the default
value is 32768 for all transports.
sec=mode
Set the security mode for NFS transactions. If sec=
is not specified, then the default action is to use
AUTH_SYS over NFS version 2 mounts, use a user-
configured default auth over NFS version 3 mounts,
or to negotiate a mode over version 4 mounts.
The preferred mode for NFS version 3 mounts is the
default mode specified in /etc/nfssec.conf (see
nfssec.conf(4)) on the client. If there is no
default configured in this file or if the server
does not export using the client's default mode,
then the client picks the first mode that it sup-
ports in the array of modes returned by the server.
These alternatives are limited to the security fla-
vors listed in /etc/nfssec.conf.
NFS version 4 mounts negotiate a security mode when
the server returns an array of security modes. The
client attempts the mount with each security mode,
in order, until one is successful.
Only one mode can be specified with the sec= option.
See nfssec(5) for the available mode options.
secure
This option has been deprecated in favor of the
sec=dh option.
timeo=n
Set the NFS timeout to n tenths of a second. The
default value is 11 tenths of a second for connec-
tionless transports, and 600 tenths of a second for
connection-oriented transports. This value is
ignored for connectionless transports. Such tran-
sports might implement their own timeouts, which are
outside the control of NFS.
vers=NFS version number
By default, the version of NFS protocol used between
the client and the server is the highest one avail-
able on both systems. The default maximum for the
client is version 4. This can be changed by setting
client_versmax to a valid version number (2, 3, or
4). Use the sharectl(1M) command to manipulate the
client_versmax property. If the NFS server does not
support the client's default maximum, the next
lowest version attempted until a matching version is
found.
wsize=n
Set the write buffer size to a maximum of n bytes.
The default value is 1048576 when using connection-
orientated transports with version 3 or version 4 of
the NFS protocol, and 32768 when using connection-
less transports. The default can be negotiated down
if the server prefers a smaller transfer size.
"Write" operations may not necessarily use the max-
imum buffer size. When using version 2, the default
value is 32768 for all transports.
xattr | noxattr
Allow or disallow the creation and manipulation of
extended attributes. The default is xattr. See
fsattr(5) for a description of extended attributes.
-O
Overlay mount. Allow the file system to be mounted over
an existing mount point, making the underlying file sys-
tem inaccessible. If a mount is attempted on a pre-
existing mount point without setting this flag, the
mount fails, producing the error "device busy."
idmap
By default, this option is not used during the mount. If
the "idmap" mount option is not used, AUTH_SYS authenti-
cation is based on the equality between the client sup-
plied UID/GID in the RPC credential and the UID/GID
stored in the NFS server. In effect, it disables the
nfsmapid functionality, which can make migration from
legacy NFSv2/v3 systems to NFSv4 easier. NFS clients
automatically detect the servers which do not support
numeric string UIDs and GIDs, and automatically fall
back to user@domain format. Use the idmap mount option
to turn off this behavior, that is, turning off numeric
strings UIDs and GIDs support.
NFS File Systems
Background versus Foreground
File systems mounted with the bg option indicate that
mount is to retry in the background if the server's
mount daemon (mountd(1M)) does not respond. mount
retries the request up to the count specified in the
retry=n option. (Note that the default value for retry
differs between mount and automount. See the description
of retry, above.) Once the file system is mounted, each
NFS request made in the kernel waits timeo=n tenths of a
second for a response. If no response arrives, the
time-out is multiplied by 2 and the request is
retransmitted. When the number of retransmissions has
reached the number specified in the retrans=n option, a
file system mounted with the soft option returns an
error on the request; one mounted with the hard option
prints a warning message and continues to retry the
request.
Hard versus Soft
File systems that are mounted read-write or that contain
executable files should always be mounted with the hard
option. Applications using soft mounted file systems can
incur unexpected I/O errors, file corruption, and unex-
pected program core dumps. The soft option is not recom-
mended.
Authenticated requests
The server can require authenticated NFS requests from
the client. sec=dh authentication might be required. See
nfssec(5).
URLs and the public option
If the public option is specified, or if the resource
includes and NFS URL, mount attempts to connect to the
server using the public file handle lookup protocol. See
WebNFS Client Specification, RFC 2054. If the server
supports the public file handle, the attempt is success-
ful; mount does not need to contact the server's
rpcbind(1M) and the mountd(1M) daemons to get the port
number of the mount server and the initial file handle
of pathname, respectively. If the NFS client and server
are separated by a firewall that allows all outbound
connections through specific ports, such as NFS_PORT,
then this enables NFS operations through the firewall.
The public option and the NFS URL can be specified
independently or together. They interact as specified in
the following matrix:
Resource Style
host:pathname NFS URL
public option Force public file Force public file
handle and fail handle and fail
mount if not supported. mount if not supported.
Use Native paths. Use Canonical paths.
default Use MOUNT protocol. Try public file handle
with Canonical paths.
Fall back to MOUNT
protocol if not
supported.
A Native path is a path name that is interpreted accord-
ing to conventions used on the native operating system
of the NFS server. A Canonical path is a path name that
is interpreted according to the URL rules. See Uniform
Resource Locators (URL), RFC 1738. See "Examples,"
below, for uses of Native and Canonical paths.
Replicated file systems and failover
resource can list multiple read-only file systems to be
used to provide data. These file systems should contain
equivalent directory structures and identical files. The
file systems can be specified either with a
comma-separated list of host:/pathname entries and/or
NFS URL entries, or with a comma -separated list of
hosts, if all file system names are the same. If multi-
ple file systems are named and the first server in the
list is down, failover uses the next alternate server to
access files. If the read-only option is not chosen,
replication is disabled. File access, for NFS versions 2
and 3, is blocked on the original if NFS locks are
active for that file.
File Attributes
To improve NFS read performance, files and file attributes
are cached. File modification times get updated whenever a
write occurs. However, file access times can be temporarily
out-of-date until the cache gets refreshed.
The attribute cache retains file attributes on the client.
Attributes for a file are assigned a time to be flushed. If
the file is modified before the flush time, then the flush
time is extended by the time since the last modification
(under the assumption that files that changed recently are
likely to change soon). There is a minimum and maximum flush
time extension for regular files and for directories. Set-
ting actimeo=n sets flush time to n seconds for both regular
files and directories.
Setting actimeo=0 disables attribute caching on the client.
This means that every reference to attributes is satisfied
directly from the server though file data is still cached.
While this guarantees that the client always has the latest
file attributes from the server, it has an adverse effect on
performance through additional latency, network load, and
server load.
Setting the noac option also disables attribute caching, but
has the further effect of disabling client write caching.
While this guarantees that data written by an application is
written directly to a server, where it can be viewed immedi-
ately by other clients, it has a significant adverse effect
on client write performance. Data written into memory-mapped
file pages (mmap(2)) are not written directly to this
server.
Specifying Values for Attribute Cache Duration Options
The attribute cache duration options are acdirmax, acdirmin,
acregmax, acregmin, and actimeo, as described under OPTIONS.
A value specified for actimeo sets the values of all attri-
bute cache duration options except for any of these options
specified following actimeo on a mount command line. For
example, consider the following command:
example# mount -o acdirmax=10,actimeo=1000 server:/path /localpath
Because actimeo is the last duration option in the command
line, its value (1000) becomes the setting for all of the
duration options, including acdirmax. Now consider:
example# mount -o actimeo=1000,acdirmax=10 server:/path /localpath
Because the acdirmax option follows actimeo on the command
line, it is assigned the value specified (10). The remaining
duration options are set to the value of actimeo (1000).
Examples
Example 1 Mounting an NFS File System
To mount an NFS file system:
example# mount serv:/usr/src /usr/src
This is an example of the use of a native path.
Example 2 Mounting An NFS File System Read-Only With No suid
Privileges
To mount an NFS file system read-only with no suid
privileges:
example# mount -r -o nosuid serv:/usr/src /usr/src
Example 3 Mounting An NFS File System Over Version 2, with
the UDP Transport
To mount an NFS file system over version 2, with the UDP
transport:
example# mount -o vers=2,proto=udp serv:/usr/src /usr/src
Example 4 Mounting an NFS File System Using An NFS URL
To mount an NFS file system using an NFS URL (a canonical
path):
example# mount nfs://serv/usr/man /usr/man
Example 5 Mounting An NFS File System Forcing Use Of The
Public File Handle
To mount an NFS file system and force the use of the public
file handle and an NFS URL (a canonical path) that has a non
7-bit ASCII escape sequence:
example# mount -o public nfs://serv/usr/%A0abc /mnt/test
Example 6 Mounting an NFS File System Using a Native Path
To mount an NFS file system using a native path (where the
server uses colons (":") as the component separator) and the
public file handle:
example# mount -o public serv:C:doc:new /usr/doc
Example 7 Mounting a Replicated Set of NFS File Systems with
the Same Pathnames
To mount a replicated set of NFS file systems with the same
pathnames:
example# mount serv-a,serv-b,serv-c:/usr/man /usr/man
Example 8 Mounting a Replicated Set of NFS File Systems with
Different Pathnames
To mount a replicated set of NFS file systems with different
pathnames:
example# mount serv-x:/usr/man,serv-y:/var/man,nfs://serv-z/man /usr/man
Files
/etc/mnttab
table of mounted file systems
/etc/dfs/fstypes
default distributed file system type
/etc/vfstab
table of automatically mounted resources
Attributes
See attributes(5) for descriptions of the following attri-
butes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRI-
BUTE TYPEATTRIBUTE VALUE _ Availabilitysystem/file-
system/nfs
See Also
lockd(1M), mountall(1M), mountd(1M), nfsd(1M), quota(1M),
sharectl(1M), statd(1M), mkdir(2), mmap(2), mount(2),
open(2), umount(2), mnttab(4), nfssec.conf(4), attributes(5),
fsattr(5), nfssec(5), standards(5), inet(7P),
inet6(7P), lofs(7FS)
Callaghan, Brent, WebNFS Client Specification, RFC 2054,
October 1996.
Callaghan, Brent, NFS URL Scheme, RFC 2224, October 1997.
Berners-Lee, Masinter & McCahill , Uniform Resource Locators
(URL), RFC 1738, December 1994.
Notes
An NFS server should not attempt to mount its own file sys-
tems. An NFS server can mount its own file systems only if
it is provided by ZFS. See lofs(7FS).
If the directory on which a file system is to be mounted is
a symbolic link, the file system is mounted on the directory
to which the symbolic link refers, rather than being mounted
on top of the symbolic link itself.
SunOS 4.x used the biod maintenance procedure to perform
parallel read-ahead and write-behind on NFS clients. SunOS
5.x made biod obsolete with multi-threaded processing, which
transparently performs parallel read-ahead and write-behind.
Since the root (/) file system is mounted read-only by the
kernel during the boot process, only the remount option (and
options that can be used in conjunction with remount) affect
the root (/) entry in the /etc/vfstab file.