Options

See mount(8) for the list of supported generic_options. See share_nfs(8) for a description of server options.

-o specific_options

Set file system specific options according to a comma-separated list with no intervening spaces.

The following list describes specific_options:

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. 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.

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 possibility 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(8) on the server. See standards(7) 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(8) 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.

rsize=n

Set the read buffer size to a maximum of n bytes. The default value is 1048576 when using connection-oriented 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 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(5)) 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 successful.

Only one mode can be specified with the sec= option. See nfssec(7) 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 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 available on both systems. If the NFS server does not support the client's default maximum, the next lowest version attempted until a matching version is found. See nfs(5) for more information on setting default minimum and maximum client versions.

wsize=n

Set the write buffer size to a maximum of n bytes. The default value is 1048576 when using connection-oriented 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 transports.

xattr|noxattr

Allow or disallow the creation and manipulation of extended attributes. The default is xattr. See fsattr(7) for a description of extended attributes.

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(8)) 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 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(7).

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 RFC 2054, WebNFS Client Specification. If the server supports the public file handle, the attempt is successful; mount does not need to contact the server's rpcbind(8) and the mountd(8) 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 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 RFC 1738, Uniform Resource Locators (URL).

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 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 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. 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 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 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).