mount_nfs(1M)
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.
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
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.
nfs://host[:port]/pathname resources
A comma-
separated list of host:pathname and/or
See the discussion of replicated file systems and
failover under NFS FILE SYSTEMS for a more detailed
discussion.
A comma-
separated list of hosts followed by a :pathname suffix
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).
OPTIONS
See mount(1M) for the list of supported generic_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
directories to n seconds.
bg | fg
If the first attempt fails, retry in the back-
ground, 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 for-
cedirectio, 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 may 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.
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 may 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 con-
sistency. 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 regard-
ing POSIX.
proto=<netid>
<netid> is a value of network_id field from
entry in the /etc/netconfig file. By default,
the transport protocol used for the NFS mount is
the first available connection oriented tran-
sport supported on both the client and the
server. If no connection oriented transport is
found, then the first available connectionless
transport is used. This default behavior can be
overridden with the proto=<netid> option.
public
The public option forces the use of the public
file handle when connecting to the NFS server.
The resource specified may or may not have an
NFS URL. See the discussion of URL's 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
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 opera-
tion. 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.
ro | rw
resource is mounted read-only or read-write. The
default is rw.
rsize=n
Set the read buffer size to n bytes. The default
value is 32768 when using Version 3 of the NFS
protocol. The default can be negotiated down if
the server prefers a smaller transfer size. When
using Version 2, the default value is 8192.
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, or
to negotiate a mode over NFS Version 3 mounts.
NFS Version 3 mounts negotiate a security mode
when the server returns an array of security
modes. The client picks the first mode in the
array that is supported on the client. 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.
suid | nosuid
Allow or disallow setuid execution. The default
is suid.
timeo=n
Set the NFS timeout to n tenths of a second. The
default value is 11 tenths of a second for con-
nectionless transports, and 600 tenths of a
second for connection-oriented transports.
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. If the NFS server
does not support NFS Version 3 protocol, then
the NFS mount uses NFS Version 2 protocol.
wsize=n
Set the write buffer size to n bytes. The
default value is 32768 when using Version 3 of
the NFS protocol. The default can be negotiated
down if the server prefers a smaller transfer
size. When using Version 2, the default value is
8192.
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 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 specified in the
retry=n option. (Note that the default value for retry
differs between mount and automount. See the descrip-
tion 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 con-
tain executable files should always be mounted with
the hard option. Applications using soft mounted file
systems may incur unexpected I/O errors, file corrup-
tion, and unexpected program core dumps. The soft
option is not recommended.
Authenticated requests
The server may 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 ini-
tial 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 opera-
tions 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 sup- mount if not sup-
ported. ported.
_________________________________________________________________
Use Native paths. Use Canonical paths.
_________________________________________________________________
default Use MOUNT protocol. Try public file han-
dle with Canonical
paths. Fall back to
MOUNT protocol if
not supported.
_________________________________________________________________
| | | |
|A Native path is a |path name that is |interpreted |
|according 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 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. It is also recommended that they be created by |
|a utility such as rdist(1). The file systems may 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 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 dis- |
|abled. File access 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 may 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.
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
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Availability | SUNWnfscu |
|_____________________________|_____________________________|
SEE ALSO
rdist(1), mountall(1M), mountd(1M), quota(1M), mkdir(2),
mmap(2), mount(2), open(2), umount(2), mnttab(4), attri-
butes(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. 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.
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