The mount utility attaches a named resource to the file system 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 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 specifying 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.

A comma-separated list of host:pathname and/or nfs://host[:port]/pathname resources

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).

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 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 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 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>

<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 transport 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 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.

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 connectionless 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."

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 may incur unexpected I/O errors, file corruption, 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 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 handle and fail mount if not supported.	Force public file handle and fail 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 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 disabled. File access is blocked on the original if NFS locks are active for that file.

File Attributes

/etc/mnttab

table of mounted file systems

/etc/dfs/fstypes

default distributed file system type

/etc/vfstab

table of automatically mounted resources

See attributes(5) for descriptions of the following attributes:

rdist(1), mountall(1M), mountd(1M), quota(1M), mkdir(2), mmap(2), mount(2), open(2), umount(2), mnttab(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.

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 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.