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   nfs    ( 5 )

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Параметры монтирования (Mount options)

Refer to mount(8) for a description of generic mount options available for all file systems. If you do not need to specify any mount options, use the generic option defaults in /etc/fstab.

Options supported by all versions These options are valid to use with any NFS version.

nfsvers=n The NFS protocol version number used to contact the server's NFS service. If the server does not support the requested version, the mount request fails. If this option is not specified, the client tries version 4.2 first, then negotiates down until it finds a version supported by the server.

vers=n This option is an alternative to the nfsvers option. It is included for compatibility with other operating systems

soft / hard Determines the recovery behavior of the NFS client after an NFS request times out. If neither option is specified (or if the hard option is specified), NFS requests are retried indefinitely. If the soft option is specified, then the NFS client fails an NFS request after retrans retransmissions have been sent, causing the NFS client to return an error to the calling application.

NB: A so-called "soft" timeout can cause silent data corruption in certain cases. As such, use the soft option only when client responsiveness is more important than data integrity. Using NFS over TCP or increasing the value of the retrans option may mitigate some of the risks of using the soft option.

softreval / nosoftreval In cases where the NFS server is down, it may be useful to allow the NFS client to continue to serve up paths and attributes from cache after retrans attempts to revalidate that cache have timed out. This may, for instance, be helpful when trying to unmount a filesystem tree from a server that is permanently down.

It is possible to combine softreval with the soft mount option, in which case operations that cannot be served up from cache will time out and return an error after retrans attempts. The combination with the default hard mount option implies those uncached operations will continue to retry until a response is received from the server.

Note: the default mount option is nosoftreval which disallows fallback to cache when revalidation fails, and instead follows the behavior dictated by the hard or soft mount option.

intr / nointr This option is provided for backward compatibility. It is ignored after kernel 2.6.25.

timeo=n The time in deciseconds (tenths of a second) the NFS client waits for a response before it retries an NFS request.

For NFS over TCP the default timeo value is 600 (60 seconds). The NFS client performs linear backoff: After each retransmission the timeout is increased by timeo up to the maximum of 600 seconds.

However, for NFS over UDP, the client uses an adaptive algorithm to estimate an appropriate timeout value for frequently used request types (such as READ and WRITE requests), but uses the timeo setting for infrequently used request types (such as FSINFO requests). If the timeo option is not specified, infrequently used request types are retried after 1.1 seconds. After each retransmission, the NFS client doubles the timeout for that request, up to a maximum timeout length of 60 seconds.

retrans=n The number of times the NFS client retries a request before it attempts further recovery action. If the retrans option is not specified, the NFS client tries each UDP request three times and each TCP request twice.

The NFS client generates a "server not responding" message after retrans retries, then attempts further recovery (depending on whether the hard mount option is in effect).

rsize=n The maximum number of bytes in each network READ request that the NFS client can receive when reading data from a file on an NFS server. The actual data payload size of each NFS READ request is equal to or smaller than the rsize setting. The largest read payload supported by the Linux NFS client is 1,048,576 bytes (one megabyte).

The rsize value is a positive integral multiple of 1024. Specified rsize values lower than 1024 are replaced with 4096; values larger than 1048576 are replaced with 1048576. If a specified value is within the supported range but not a multiple of 1024, it is rounded down to the nearest multiple of 1024.

If an rsize value is not specified, or if the specified rsize value is larger than the maximum that either client or server can support, the client and server negotiate the largest rsize value that they can both support.

The rsize mount option as specified on the mount(8) command line appears in the /etc/mtab file. However, the effective rsize value negotiated by the client and server is reported in the /proc/mounts file.

wsize=n The maximum number of bytes per network WRITE request that the NFS client can send when writing data to a file on an NFS server. The actual data payload size of each NFS WRITE request is equal to or smaller than the wsize setting. The largest write payload supported by the Linux NFS client is 1,048,576 bytes (one megabyte).

Similar to rsize , the wsize value is a positive integral multiple of 1024. Specified wsize values lower than 1024 are replaced with 4096; values larger than 1048576 are replaced with 1048576. If a specified value is within the supported range but not a multiple of 1024, it is rounded down to the nearest multiple of 1024.

If a wsize value is not specified, or if the specified wsize value is larger than the maximum that either client or server can support, the client and server negotiate the largest wsize value that they can both support.

The wsize mount option as specified on the mount(8) command line appears in the /etc/mtab file. However, the effective wsize value negotiated by the client and server is reported in the /proc/mounts file.

ac / noac Selects whether the client may cache file attributes. If neither option is specified (or if ac is specified), the client caches file attributes.

To improve performance, NFS clients cache file attributes. Every few seconds, an NFS client checks the server's version of each file's attributes for updates. Changes that occur on the server in those small intervals remain undetected until the client checks the server again. The noac option prevents clients from caching file attributes so that applications can more quickly detect file changes on the server.

In addition to preventing the client from caching file attributes, the noac option forces application writes to become synchronous so that local changes to a file become visible on the server immediately. That way, other clients can quickly detect recent writes when they check the file's attributes.

Using the noac option provides greater cache coherence among NFS clients accessing the same files, but it extracts a significant performance penalty. As such, judicious use of file locking is encouraged instead. The DATA AND METADATA COHERENCE section contains a detailed discussion of these trade-offs.

acregmin=n The minimum time (in seconds) that the NFS client caches attributes of a regular file before it requests fresh attribute information from a server. If this option is not specified, the NFS client uses a 3-second minimum. See the DATA AND METADATA COHERENCE section for a full discussion of attribute caching.

acregmax=n The maximum time (in seconds) that the NFS client caches attributes of a regular file before it requests fresh attribute information from a server. If this option is not specified, the NFS client uses a 60-second maximum. See the DATA AND METADATA COHERENCE section for a full discussion of attribute caching.

acdirmin=n The minimum time (in seconds) that the NFS client caches attributes of a directory before it requests fresh attribute information from a server. If this option is not specified, the NFS client uses a 30-second minimum. See the DATA AND METADATA COHERENCE section for a full discussion of attribute caching.

acdirmax=n The maximum time (in seconds) that the NFS client caches attributes of a directory before it requests fresh attribute information from a server. If this option is not specified, the NFS client uses a 60-second maximum. See the DATA AND METADATA COHERENCE section for a full discussion of attribute caching.

actimeo=n Using actimeo sets all of acregmin, acregmax, acdirmin, and acdirmax to the same value. If this option is not specified, the NFS client uses the defaults for each of these options listed above.

bg / fg Determines how the mount(8) command behaves if an attempt to mount an export fails. The fg option causes mount(8) to exit with an error status if any part of the mount request times out or fails outright. This is called a "foreground" mount, and is the default behavior if neither the fg nor bg mount option is specified.

If the bg option is specified, a timeout or failure causes the mount(8) command to fork a child which continues to attempt to mount the export. The parent immediately returns with a zero exit code. This is known as a "background" mount.

If the local mount point directory is missing, the mount(8) command acts as if the mount request timed out. This permits nested NFS mounts specified in /etc/fstab to proceed in any order during system initialization, even if some NFS servers are not yet available. Alternatively these issues can be addressed using an automounter (refer to automount(8) for details).

nconnect=n When using a connection oriented protocol such as TCP, it may sometimes be advantageous to set up multiple connections between the client and server. For instance, if your clients and/or servers are equipped with multiple network interface cards (NICs), using multiple connections to spread the load may improve overall performance. In such cases, the nconnect option allows the user to specify the number of connections that should be established between the client and server up to a limit of 16.

Note that the nconnect option may also be used by some pNFS drivers to decide how many connections to set up to the data servers.

rdirplus / nordirplus Selects whether to use NFS v3 or v4 READDIRPLUS requests. If this option is not specified, the NFS client uses READDIRPLUS requests on NFS v3 or v4 mounts to read small directories. Some applications perform better if the client uses only READDIR requests for all directories.

retry=n The number of minutes that the mount(8) command retries an NFS mount operation in the foreground or background before giving up. If this option is not specified, the default value for foreground mounts is 2 minutes, and the default value for background mounts is 10000 minutes (80 minutes shy of one week). If a value of zero is specified, the mount(8) command exits immediately after the first failure.

Note that this only affects how many retries are made and doesn't affect the delay caused by each retry. For UDP each retry takes the time determined by the timeo and retrans options, which by default will be about 7 seconds. For TCP the default is 3 minutes, but system TCP connection timeouts will sometimes limit the timeout of each retransmission to around 2 minutes.

sec=flavors A colon-separated list of one or more security flavors to use for accessing files on the mounted export. If the server does not support any of these flavors, the mount operation fails. If sec= is not specified, the client attempts to find a security flavor that both the client and the server supports. Valid flavors are none, sys, krb5, krb5i, and krb5p. Refer to the SECURITY CONSIDERATIONS section for details.

sharecache / nosharecache Determines how the client's data cache and attribute cache are shared when mounting the same export more than once concurrently. Using the same cache reduces memory requirements on the client and presents identical file contents to applications when the same remote file is accessed via different mount points.

If neither option is specified, or if the sharecache option is specified, then a single cache is used for all mount points that access the same export. If the nosharecache option is specified, then that mount point gets a unique cache. Note that when data and attribute caches are shared, the mount options from the first mount point take effect for subsequent concurrent mounts of the same export.

As of kernel 2.6.18, the behavior specified by nosharecache is legacy caching behavior. This is considered a data risk since multiple cached copies of the same file on the same client can become out of sync following a local update of one of the copies.

resvport / noresvport Specifies whether the NFS client should use a privileged source port when communicating with an NFS server for this mount point. If this option is not specified, or the resvport option is specified, the NFS client uses a privileged source port. If the noresvport option is specified, the NFS client uses a non-privileged source port. This option is supported in kernels 2.6.28 and later.

Using non-privileged source ports helps increase the maximum number of NFS mount points allowed on a client, but NFS servers must be configured to allow clients to connect via non-privileged source ports.

Refer to the SECURITY CONSIDERATIONS section for important details.

lookupcache=mode Specifies how the kernel manages its cache of directory entries for a given mount point. mode can be one of all, none, pos, or positive. This option is supported in kernels 2.6.28 and later.

The Linux NFS client caches the result of all NFS LOOKUP requests. If the requested directory entry exists on the server, the result is referred to as positive. If the requested directory entry does not exist on the server, the result is referred to as negative.

If this option is not specified, or if all is specified, the client assumes both types of directory cache entries are valid until their parent directory's cached attributes expire.

If pos or positive is specified, the client assumes positive entries are valid until their parent directory's cached attributes expire, but always revalidates negative entires before an application can use them.

If none is specified, the client revalidates both types of directory cache entries before an application can use them. This permits quick detection of files that were created or removed by other clients, but can impact application and server performance.

The DATA AND METADATA COHERENCE section contains a detailed discussion of these trade-offs.

fsc / nofsc Enable/Disables the cache of (read-only) data pages to the local disk using the FS-Cache facility. See cachefilesd(8) and <kernel_source>/Documentation/filesystems/caching for detail on how to configure the FS-Cache facility. Default value is nofsc.

sloppy The sloppy option is an alternative to specifying mount.nfs -s option.

Options for NFS versions 2 and 3 only Use these options, along with the options in the above subsection, for NFS versions 2 and 3 only.

proto=netid The netid determines the transport that is used to communicate with the NFS server. Available options are udp, udp6, tcp, tcp6, rdma, and rdma6. Those which end in 6 use IPv6 addresses and are only available if support for TI-RPC is built in. Others use IPv4 addresses.

Each transport protocol uses different default retrans and timeo settings. Refer to the description of these two mount options for details.

In addition to controlling how the NFS client transmits requests to the server, this mount option also controls how the mount(8) command communicates with the server's rpcbind and mountd services. Specifying a netid that uses TCP forces all traffic from the mount(8) command and the NFS client to use TCP. Specifying a netid that uses UDP forces all traffic types to use UDP.

Before using NFS over UDP, refer to the TRANSPORT METHODS section.

If the proto mount option is not specified, the mount(8) command discovers which protocols the server supports and chooses an appropriate transport for each service. Refer to the TRANSPORT METHODS section for more details.

udp The udp option is an alternative to specifying proto=udp. It is included for compatibility with other operating systems.

Before using NFS over UDP, refer to the TRANSPORT METHODS section.

tcp The tcp option is an alternative to specifying proto=tcp. It is included for compatibility with other operating systems.

rdma The rdma option is an alternative to specifying proto=rdma.

port=n The numeric value of the server's NFS service port. If the server's NFS service is not available on the specified port, the mount request fails.

If this option is not specified, or if the specified port value is 0, then the NFS client uses the NFS service port number advertised by the server's rpcbind service. The mount request fails if the server's rpcbind service is not available, the server's NFS service is not registered with its rpcbind service, or the server's NFS service is not available on the advertised port.

mountport=n The numeric value of the server's mountd port. If the server's mountd service is not available on the specified port, the mount request fails.

If this option is not specified, or if the specified port value is 0, then the mount(8) command uses the mountd service port number advertised by the server's rpcbind service. The mount request fails if the server's rpcbind service is not available, the server's mountd service is not registered with its rpcbind service, or the server's mountd service is not available on the advertised port.

This option can be used when mounting an NFS server through a firewall that blocks the rpcbind protocol.

mountproto=netid The transport the NFS client uses to transmit requests to the NFS server's mountd service when performing this mount request, and when later unmounting this mount point.

netid may be one of udp, and tcp which use IPv4 address or, if TI-RPC is built into the mount.nfs command, udp6, and tcp6 which use IPv6 addresses.

This option can be used when mounting an NFS server through a firewall that blocks a particular transport. When used in combination with the proto option, different transports for mountd requests and NFS requests can be specified. If the server's mountd service is not available via the specified transport, the mount request fails.

Refer to the TRANSPORT METHODS section for more on how the mountproto mount option interacts with the proto mount option.

mounthost=name The hostname of the host running mountd. If this option is not specified, the mount(8) command assumes that the mountd service runs on the same host as the NFS service.

mountvers=n The RPC version number used to contact the server's mountd. If this option is not specified, the client uses a version number appropriate to the requested NFS version. This option is useful when multiple NFS services are running on the same remote server host.

namlen=n The maximum length of a pathname component on this mount. If this option is not specified, the maximum length is negotiated with the server. In most cases, this maximum length is 255 characters.

Some early versions of NFS did not support this negotiation. Using this option ensures that pathconf(3) reports the proper maximum component length to applications in such cases.

lock / nolock Selects whether to use the NLM sideband protocol to lock files on the server. If neither option is specified (or if lock is specified), NLM locking is used for this mount point. When using the nolock option, applications can lock files, but such locks provide exclusion only against other applications running on the same client. Remote applications are not affected by these locks.

NLM locking must be disabled with the nolock option when using NFS to mount /var because /var contains files used by the NLM implementation on Linux. Using the nolock option is also required when mounting exports on NFS servers that do not support the NLM protocol.

cto / nocto Selects whether to use close-to-open cache coherence semantics. If neither option is specified (or if cto is specified), the client uses close-to-open cache coherence semantics. If the nocto option is specified, the client uses a non-standard heuristic to determine when files on the server have changed.

Using the nocto option may improve performance for read- only mounts, but should be used only if the data on the server changes only occasionally. The DATA AND METADATA COHERENCE section discusses the behavior of this option in more detail.

acl / noacl Selects whether to use the NFSACL sideband protocol on this mount point. The NFSACL sideband protocol is a proprietary protocol implemented in Solaris that manages Access Control Lists. NFSACL was never made a standard part of the NFS protocol specification.

If neither acl nor noacl option is specified, the NFS client negotiates with the server to see if the NFSACL protocol is supported, and uses it if the server supports it. Disabling the NFSACL sideband protocol may be necessary if the negotiation causes problems on the client or server. Refer to the SECURITY CONSIDERATIONS section for more details.

local_lock=mechanism Specifies whether to use local locking for any or both of the flock and the POSIX locking mechanisms. mechanism can be one of all, flock, posix, or none. This option is supported in kernels 2.6.37 and later.

The Linux NFS client provides a way to make locks local. This means, the applications can lock files, but such locks provide exclusion only against other applications running on the same client. Remote applications are not affected by these locks.

If this option is not specified, or if none is specified, the client assumes that the locks are not local.

If all is specified, the client assumes that both flock and POSIX locks are local.

If flock is specified, the client assumes that only flock locks are local and uses NLM sideband protocol to lock files when POSIX locks are used.

If posix is specified, the client assumes that POSIX locks are local and uses NLM sideband protocol to lock files when flock locks are used.

To support legacy flock behavior similar to that of NFS clients < 2.6.12, use 'local_lock=flock'. This option is required when exporting NFS mounts via Samba as Samba maps Windows share mode locks as flock. Since NFS clients > 2.6.12 implement flock by emulating POSIX locks, this will result in conflicting locks.

NOTE: When used together, the 'local_lock' mount option will be overridden by 'nolock'/'lock' mount option.

Options for NFS version 4 only Use these options, along with the options in the first subsection above, for NFS version 4.0 and newer.

proto=netid The netid determines the transport that is used to communicate with the NFS server. Supported options are tcp, tcp6, rdma, and rdma6. tcp6 use IPv6 addresses and is only available if support for TI-RPC is built in. Both others use IPv4 addresses.

All NFS version 4 servers are required to support TCP, so if this mount option is not specified, the NFS version 4 client uses the TCP protocol. Refer to the TRANSPORT METHODS section for more details.

minorversion=n Specifies the protocol minor version number. NFSv4 introduces "minor versioning," where NFS protocol enhancements can be introduced without bumping the NFS protocol version number. Before kernel 2.6.38, the minor version is always zero, and this option is not recognized. After this kernel, specifying "minorversion=1" enables a number of advanced features, such as NFSv4 sessions.

Recent kernels allow the minor version to be specified using the vers= option. For example, specifying vers=4.1 is the same as specifying vers=4,minorversion=1.

port=n The numeric value of the server's NFS service port. If the server's NFS service is not available on the specified port, the mount request fails.

If this mount option is not specified, the NFS client uses the standard NFS port number of 2049 without first checking the server's rpcbind service. This allows an NFS version 4 client to contact an NFS version 4 server through a firewall that may block rpcbind requests.

If the specified port value is 0, then the NFS client uses the NFS service port number advertised by the server's rpcbind service. The mount request fails if the server's rpcbind service is not available, the server's NFS service is not registered with its rpcbind service, or the server's NFS service is not available on the advertised port.

cto / nocto Selects whether to use close-to-open cache coherence semantics for NFS directories on this mount point. If neither cto nor nocto is specified, the default is to use close-to-open cache coherence semantics for directories.

File data caching behavior is not affected by this option. The DATA AND METADATA COHERENCE section discusses the behavior of this option in more detail.

clientaddr=n.n.n.n

clientaddr=n:n:...:n Specifies a single IPv4 address (in dotted-quad form), or a non-link-local IPv6 address, that the NFS client advertises to allow servers to perform NFS version 4.0 callback requests against files on this mount point. If the server is unable to establish callback connections to clients, performance may degrade, or accesses to files may temporarily hang. Can specify a value of IPv4_ANY (0.0.0.0) or equivalent IPv6 any address which will signal to the NFS server that this NFS client does not want delegations.

If this option is not specified, the mount(8) command attempts to discover an appropriate callback address automatically. The automatic discovery process is not perfect, however. In the presence of multiple client network interfaces, special routing policies, or atypical network topologies, the exact address to use for callbacks may be nontrivial to determine.

NFS protocol versions 4.1 and 4.2 use the client- established TCP connection for callback requests, so do not require the server to connect to the client. This option is therefore only affect NFS version 4.0 mounts.

migration / nomigration Selects whether the client uses an identification string that is compatible with NFSv4 Transparent State Migration (TSM). If the mounted server supports NFSv4 migration with TSM, specify the migration option.

Some server features misbehave in the face of a migration- compatible identification string. The nomigration option retains the use of a traditional client indentification string which is compatible with legacy NFS servers. This is also the behavior if neither option is specified. A client's open and lock state cannot be migrated transparently when it identifies itself via a traditional identification string.

This mount option has no effect with NFSv4 minor versions newer than zero, which always use TSM-compatible client identification strings.