file describes how
.BR mount (8)
should assemble a system's file name hierarchy
-from various independent file systems
+from various independent file systems
(including file systems exported by NFS servers).
Each line in the
.I /etc/fstab
.P
The server's hostname and export pathname
are separated by a colon, while
-the mount options are separated by commas. The remaining fields
+the mount options are separated by commas. The remaining fields
are separated by blanks or tabs.
The server's hostname can be an unqualified hostname,
a fully qualified domain name,
and
.B nfs4
file system types share similar mount options,
-which are described below.
+which are described below.
.SH "MOUNT OPTIONS"
-Refer to
+Refer to
.BR 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
+available for all file systems. If you do not need to
+specify any mount options, use the generic option
.B defaults
in
.IR /etc/fstab .
-.
.DT
.SS "Valid options for either the nfs or nfs4 file system type"
These options are valid to use when mounting either
If the
.B soft
option is specified, then the NFS client fails an NFS request
-after
+after
.B retrans
retransmissions have been sent,
causing the NFS client to return an error
option.
.TP 1.5i
.BI timeo= n
-The time (in tenths of a second) the NFS client waits for a
-response before it retries an NFS request. If this
+The time (in tenths of a second) the NFS client waits for a
+response before it retries an NFS request. If this
option is not specified, requests are retried every
60 seconds for NFS over TCP.
The NFS client does not perform any kind of timeout backoff
.IP
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
+request types (such as READ and WRITE requests), but uses the
.B timeo
setting for infrequently used request types (such as FSINFO requests).
If the
.TP 1.5i
.BI retrans= n
The number of times the NFS client retries a request before
-it attempts further recovery action. If the
+it attempts further recovery action. If the
.B retrans
-option is not specified, the NFS client tries each request
+option is not specified, the NFS client tries each request
three times.
.IP
The NFS client generates a "server not responding" message
-after
+after
.B retrans
retries, then attempts further recovery (depending on whether the
.B hard
The
.B rsize
value is a positive integral multiple of 1024.
-Specified
+Specified
.B 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
+range but not a multiple of 1024, it is rounded down to the nearest
multiple of 1024.
.IP
If an
.B rsize
-value is not specified, or if the specified
-.B rsize
+value is not specified, or if the specified
+.B rsize
value is larger than the maximum that either client or server can support,
the client and server negotiate the largest
.B rsize
-value that they can both support.
+value that they can both support.
.IP
The
.B rsize
.BI 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
+on an NFS server. The actual data payload size of each
NFS WRITE request is equal to
or smaller than the
.B wsize
Similar to
.B rsize
, the
-.B wsize
+.B wsize
value is a positive integral multiple of 1024.
-Specified
+Specified
.B 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
+range but not a multiple of 1024, it is rounded down to the nearest
multiple of 1024.
.IP
If a
.B wsize
-value is not specified, or if the specified
-.B wsize
+value is not specified, or if the specified
+.B wsize
value is larger than the maximum that either client or server can support,
the client and server negotiate the largest
.B wsize
.B wsize
value negotiated by the client and server is reported in the
.I /proc/mounts
-file.
+file.
.TP 1.5i
.BR ac " / " noac
-Selects whether the client may cache file attributes. If neither
-option is specified (or if
+Selects whether the client may cache file attributes. If neither
+option is specified (or if
.B ac
-is specified), the client caches file
-attributes.
+is specified), the client caches file
+attributes.
.IP
-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
+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
.B noac
-option prevents clients from caching file
-attributes so that applications can more quickly detect file changes
+option prevents clients from caching file
+attributes so that applications can more quickly detect file changes
on the server.
.IP
-In addition to preventing the client from caching file attributes,
-the
+In addition to preventing the client from caching file attributes,
+the
.B 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
+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.
.IP
Using the
.TP 1.5i
.BR 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
+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.
.IP
-If neither option is specified, or if the
+If neither option is specified, or if the
.B sharecache
-option is
-specified, then a single cache is used for all mount points that
-access the same export. If the
+option is
+specified, then a single cache is used for all mount points that
+access the same export. If the
.B 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
+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.
.IP
As of kernel 2.6.18, the behavior specified by
the server, this mount option also controls how the
.BR mount (8)
command communicates with the server's rpcbind and mountd services.
-Specifying
+Specifying
.B proto=tcp
-forces all traffic from the
+forces all traffic from the
.BR mount (8)
command and the NFS client to use TCP.
Specifying
.TP 1.5i
.BR lock " / " nolock
Selects whether to use the NLM sideband protocol to lock files on the server.
-If neither option is specified (or if
-.B lock
-is specified), NLM locking is used for this mount point.
+If neither option is specified (or if
+.B lock
+is specified), NLM locking is used for this mount point.
When using the
.B nolock
option, applications can lock files,
.TP 1.5i
.BR intr " / " nointr
Selects whether to allow signals to interrupt file operations
-on this mount point. If neither option
-is specified (or if
+on this mount point. If neither option
+is specified (or if
.B nointr
is specified),
signals do not interrupt NFS file operations. If
-.B intr
-is specified, system calls return EINTR if an in-progress NFS operation is interrupted by
+.B intr
+is specified, system calls return EINTR if an in-progress NFS operation is interrupted by
a signal.
.IP
Using the
.TP 1.5i
.BR cto " / " nocto
Selects whether to use close-to-open cache coherence semantics.
-If neither option is specified (or if
+If neither option is specified (or if
.B cto
is specified), the client uses close-to-open
-cache coherence semantics. If the
-.B nocto
+cache coherence semantics. If the
+.B nocto
option is specified, the client uses a non-standard heuristic to determine when
-files on the server have changed.
+files on the server have changed.
.IP
Using the
.B nocto
.BR 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
+implemented in Solaris that manages Access Control Lists. NFSACL was never
made a standard part of the NFS protocol specification.
.IP
-If neither
+If neither
.B acl
-nor
-.B noacl
+nor
+.B noacl
option is specified,
the NFS client negotiates with the server
to see if the NFSACL protocol is supported,
If this option is not specified, the NFS client uses READDIRPLUS requests
on NFS version 3 mounts to read small directories.
Some applications perform better if the client uses only READDIR requests
-for all directories.
+for all directories.
.SS "Valid options for the nfs4 file system type"
Use these options, along with the options in the first subsection above,
for mounting the
or
.BR tcp .
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 transport protocol.
+so if this mount option is not specified, the NFS version 4 client
+uses the TCP transport protocol.
Refer to the TRANSPORT METHODS section for more details.
.TP 1.5i
.BI port= n
.TP 1.5i
.BR intr " / " nointr
Selects whether to allow signals to interrupt file operations
-on this mount point. If neither option is specified (or if
-.B intr
-is specified), system calls return EINTR if an in-progress NFS operation
-is interrupted by a signal. If
+on this mount point. If neither option is specified (or if
+.B intr
+is specified), system calls return EINTR if an in-progress NFS operation
+is interrupted by a signal. If
.B nointr
-is specified, signals do not
+is specified, signals do not
interrupt NFS operations.
.IP
Using the
If neither
.B cto
nor
-.B nocto
+.B nocto
is specified,
the default is to use close-to-open cache coherence
semantics for directories.
the behavior of this option in more detail.
.TP 1.5i
.BI clientaddr= n.n.n.n
-Specifies a single IPv4 address (in dotted-quad form)
-that the NFS client advertises to allow servers
-to perform NFS version 4 callback requests against
-files on this mount point. If the server is unable to
-establish callback connections to clients, performance
+Specifies a single IPv4 address (in dotted-quad form)
+that the NFS client advertises to allow servers
+to perform NFS version 4 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.
.IP
If this option is not specified, the
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.
+the exact address to use for callbacks may be nontrivial to determine.
.SH EXAMPLES
To mount an export using NFS version 2,
use the
In some cases, however, it pays to specify
these settings explicitly using mount options.
.P
-Traditionally, NFS clients used the UDP transport exclusively for
-transmitting requests to servers. Though its implementation is
-simple, NFS over UDP has many limitations that prevent smooth
-operation and good performance in some common deployment
-environments. Even an insignificant packet loss rate results in the
-loss of whole NFS requests; as such, retransmit timeouts are usually
-in the subsecond range to allow clients to recover quickly from
-dropped requests, but this can result in extraneous network traffic
+Traditionally, NFS clients used the UDP transport exclusively for
+transmitting requests to servers. Though its implementation is
+simple, NFS over UDP has many limitations that prevent smooth
+operation and good performance in some common deployment
+environments. Even an insignificant packet loss rate results in the
+loss of whole NFS requests; as such, retransmit timeouts are usually
+in the subsecond range to allow clients to recover quickly from
+dropped requests, but this can result in extraneous network traffic
and server load.
.P
-However, UDP can be quite effective in specialized settings where
-the network’s MTU is large relative to NFS’s data transfer size (such
-as network environments that enable jumbo Ethernet frames). In such
-environments, trimming the
-.B rsize
-and
-.B wsize
-settings so that each
-NFS read or write request fits in just a few network frames (or even
-in a single frame) is advised. This reduces the probability that
-the loss of a single MTU-sized network frame results in the loss of
+However, UDP can be quite effective in specialized settings where
+the networks MTU is large relative to NFSs data transfer size (such
+as network environments that enable jumbo Ethernet frames). In such
+environments, trimming the
+.B rsize
+and
+.B wsize
+settings so that each
+NFS read or write request fits in just a few network frames (or even
+in a single frame) is advised. This reduces the probability that
+the loss of a single MTU-sized network frame results in the loss of
an entire large read or write request.
.P
-TCP is the default transport protocol used for all modern NFS
+TCP is the default transport protocol used for all modern NFS
implementations. It performs well in almost every conceivable
-network environment and provides excellent guarantees against data
-corruption caused by network unreliability. TCP is often a
+network environment and provides excellent guarantees against data
+corruption caused by network unreliability. TCP is often a
requirement for mounting a server through a network firewall.
.P
Under normal circumstances, networks drop packets much more
.B retrans
mount option), it assumes a network partition has occurred,
and attempts to reconnect to the server on a fresh socket. Since
-TCP itself makes network data transfer reliable,
+TCP itself makes network data transfer reliable,
.B rsize
-and
+and
.B wsize
-can safely be allowed to default to the largest values supported by
+can safely be allowed to default to the largest values supported by
both client and server, independent of the network's MTU size.
.SS "Using the mountproto mount option"
This section applies only to NFS version 2 and version 3 mounts
perfect cache coherence among their clients.
Perfect cache coherence among disparate NFS clients
is expensive to achieve, especially on wide area networks.
-As such, NFS settles for weaker cache coherence that
-satisfies the requirements of most file sharing types. Normally,
+As such, NFS settles for weaker cache coherence that
+satisfies the requirements of most file sharing types. Normally,
file sharing is completely sequential:
first client A opens a file, writes something to it, then closes it;
then client B opens the same file, and reads the changes.
that client's updates or some other client's updates
that altered the file.
.SS "Attribute caching"
-Use the
+Use the
.B noac
mount option to achieve attribute cache coherence
among multiple clients.
true cluster file system cache coherence
without some type of application serialization.
If absolute cache coherence among clients is required,
-applications should use file locking. Alternatively, applications
+applications should use file locking. Alternatively, applications
can also open their files with the O_DIRECT flag
to disable data caching entirely.
.SS "Directory entry caching"
The NFS client treats the
.B sync
mount option differently than some other file systems
-(refer to
+(refer to
.BR mount (8)
for a description of the generic
.B sync
.B sync
nor
.B async
-is specified (or if the
-.B async
+is specified (or if the
+.B async
option is specified),
the NFS client delays sending application
writes to the server
-until any of these events occur:
+until any of these events occur:
.IP
Memory pressure forces reclamation of system memory resources.
.IP
-An application flushes file data explicitly with
+An application flushes file data explicitly with
.BR sync (2),
.BR msync (2),
or
Applications can use the O_SYNC open flag to force application
writes to individual files to go to the server immediately without
the use of the
-.B sync
+.B sync
mount option.
.SS "Using file locks with NFS"
The Network Lock Manager protocol is a separate sideband protocol
.B nolock
option when using NFS to mount
.I /var
-because
-.I /var
+because
+.I /var
contains files used by the NLM implementation on Linux.
.P
Specifying the
.B nolock
option may also be advised to improve the performance
of a proprietary application which runs on a single client
-and uses file locks extensively.
+and uses file locks extensively.
.SS "NFS version 4 caching features"
The data and metadata caching behavior of NFS version 4
clients is similar to that of earlier versions.
The NFS version 4 specification mandates NFSv4 ACLs,
RPCGSS authentication, and RPCGSS security flavors
that provide per-RPC integrity checking and encryption.
-Because NFS version 4 combines the
+Because NFS version 4 combines the
function of the sideband protocols into the main NFS protocol,
the new security features apply to all NFS version 4 operations
including mounting, file locking, and so on.
Specifying
.B sec=krb5
provides cryptographic proof of a user's identity in each RPC request.
-This provides strong verification of the identity of users
+This provides strong verification of the identity of users
accessing data on the server.
Note that additional configuration besides adding this mount option
is required in order to enable Kerberos security.
-Refer to the
+Refer to the
.BR rpc.gssd (8)
man page for details.
.P
It is still possible to mount an NFS server through a firewall,
though some of the
.BR mount (8)
-command's automatic service endpoint discovery mechanisms may not work; this
+command's automatic service endpoint discovery mechanisms may not work; this
requires you to provide specific endpoint details via NFS mount options.
.P
NFS servers normally run a portmapper or rpcbind daemon to advertise
-their service endpoints to clients. Clients use the rpcbind daemon to determine:
+their service endpoints to clients. Clients use the rpcbind daemon to determine:
.IP
What network port each RPC-based service is using
.IP
-What transport protocols each RPC-based service supports
+What transport protocols each RPC-based service supports
.P
The rpcbind daemon uses a well-known port number (111) to help clients find a service endpoint.
Although NFS often uses a standard port number (2049),
.P
The NFS version 4 specification mandates a new version
of Access Control Lists that are semantically richer than POSIX ACLs.
-NFS version 4 ACLs are not fully compatible with POSIX ACLs; as such,
+NFS version 4 ACLs are not fully compatible with POSIX ACLs; as such,
some translation between the two is required
-in an environment that mixes POSIX ACLs and NFS version 4.
+in an environment that mixes POSIX ACLs and NFS version 4.
.SH FILES
.TP 1.5i
.I /etc/fstab
.br
RFC 2203 for the RPCSEC GSS API protocol specification.
.br
-RFC 3530 for the NFS version 4 specification.
+RFC 3530 for the NFS version 4 specification.
projects / nfs-utils.git / commitdiff