MOUNT_NFS(1M)MOUNT_NFS(1M)NAMEmount_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 system hierar‐
chy 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 command 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 specify‐
ing an IPv6 address string. Otherwise 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 pathname 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 necessarily 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 failover under
NFS FILE SYSTEMS for a more detailed discussion.
hostlist pathname
hostlist is a comma-separated list of hosts.
See the discussion of replicated file systems and failover under
NFS FILE SYSTEMS for a more detailed discussion.
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.
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 direc‐
tory 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 modi‐
fication. The default value is 3.
actimeo=n
Set min and max times for regular files and directories 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 effec‐
tive GID of the calling process. This behavior can be overrid‐
den 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.
noac
Suppress data and attribute caching. The data caching 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 con‐
sistency 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 infor‐
mation 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 con‐
nection oriented transport, it uses the first available connec‐
tionless 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 sys‐
tems.
retrans=n
Set the number of NFS retransmissions to n. The default value
is 5. For connection-oriented transports, 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 heav‐
ily loaded servers, where automounter traffic is dropped, caus‐
ing 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 maximum buffer size.
When using Version 2, the default value is 32768 for all trans‐
ports.
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 supports in the
array of modes returned by the server. These alternatives are
limited to the security flavors 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 success‐
ful.
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 connectionless transports, and 600
tenths of a second for connection-oriented transports. This
value is ignored for connectionless transports. Such transports
might implement their own timeouts, which are outside the con‐
trol of NFS.
vers=NFS version number
By default, the version of NFS protocol used between the client
and the server is the highest one available on both systems.
The default maximum for the client is Version 4. This can be
changed by setting the NFS_CLIENT_VERSMAX parameter in
/etc/default/nfs to a valid version (2, 3, or 4). 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 maximum buffer size.
When using Version 2, the default value is 32768 for all trans‐
ports.
xattr | noxattr
Allow or disallow the creation and manipulation of extended
attributes. The default is xattr. See fsattr(5) for a descrip‐
tion of extended attributes.
-O
Overlay mount. Allow the file system to be mounted over an existing
mount point, making the underlying file system inaccessible. If a
mount is attempted on a pre-existing mount point without setting
this flag, the mount fails, producing the error "device busy."
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 speci‐
fied 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 unexpected program core dumps. The soft option
is not recommended.
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
successful; 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 according to con‐
ventions 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 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 direc‐
tory structures and identical files. It is also recommended that
they be created by a utility such as rdist(1). 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 multiple file sys‐
tems 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.
Setting 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 immediately by other clients, it has a signifi‐
cant adverse effect on client write performance. Data written into mem‐
ory-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 attribute 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
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
SEE ALSOrdist(1), lockd(1M), mountall(1M), mountd(1M), nfsd(1M), quota(1M),
statd(1M), mkdir(2), mmap(2), mount(2), open(2), umount(2), mnttab(4),
nfs(4), nfssec.conf(4), attributes(5), fsattr(5), nfssec(5), stan‐
dards(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 systems. 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 dur‐
ing 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.
mount_cachefs cannot be used with replicated NFS mounts or any NFS Ver‐
sion 4 mount.
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.
Jul 26, 2009 MOUNT_NFS(1M)
