rpms/nfs-utils
7
0
Fork 0
Code Issues Pull Requests Releases Activity
aa7cac06fc
nfs-utils/nfs-utils-1.1.0-nfs-man.patch
Steve Dickson c0c131bf03 - Updated to latest upstream release, nfs-utils-1.1.1 
- Added the removal of sm-notify.pid to nfslock init script.
- Changed spec file to use condrestart instead of condstop when calling
    init scripts.
2008-01-05 14:27:40 +00:00

1734 lines
59 KiB
Diff
Raw Blame History

This file contains ambiguous Unicode characters

This file contains Unicode characters that might be confused with other characters. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

commit ca43d9d8c7bdbd067fb1fb4fa9d6e055f4d34ce5
Author: Steve Dickson <steved@redhat.com>
Date: Fri Jan 4 09:27:35 2008 -0500
Incorporated Chuck Lever's and Don Domingo's changes to the
nfs(5) manual page.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Don Domingo <ddomingo@redhat.com>
Signed-off-by: Steve Dickson <steved@redhat.com>
diff -up nfs-utils-1.1.1/utils/mount/nfs.man.save nfs-utils-1.1.1/utils/mount/nfs.man
--- nfs-utils-1.1.1/utils/mount/nfs.man.save 2007-10-18 23:07:28.000000000 -0400
+++ nfs-utils-1.1.1/utils/mount/nfs.man 2008-01-05 08:34:22.000000000 -0500
@@ -1,510 +1,1233 @@
-.\" nfs.5 "Rick Sladkey" <jrs@world.std.com>
-.\" Wed Feb 8 12:52:42 1995, faith@cs.unc.edu: updates for Ross Biro's
-.\" patches. "
-.TH NFS 5 "20 November 1993" "Linux 0.99" "Linux Programmer's Manual"
+.\"@(#)nfs.5"
+.TH NFS 5 "2 November 2007"
.SH NAME
-nfs \- nfs and nfs4 fstab format and options
+nfs \- fstab format and options for the
+.B nfs
+and
+.B nfs4
+file systems
.SH SYNOPSIS
-.B /etc/fstab
+.I /etc/fstab
.SH DESCRIPTION
-The
-.I fstab
-file contains information about which filesystems
-to mount where and with what options.
-For NFS mounts, it contains the server name and
-exported server directory to mount from,
-the local directory that is the mount point,
-and the NFS specific options that control
-the way the filesystem is mounted.
+NFS is an Internet Standard protocol
+created by Sun Microsystems in 1984. NFS was developed
+to allow file sharing between systems residing
+on a local area network.
+The Linux NFS client supports three versions
+of the NFS protocol:
+NFS version 2 [RFC1094],
+NFS version 3 [RFC1813],
+and NFS version 4 [RFC3530].
.P
-Three different versions of the NFS protocol are
-supported by the Linux NFS client:
-NFS version 2, NFS version 3, and NFS version 4.
-To mount via NFS version 2, use the
-.BR nfs
-file system type and specify
-.BR nfsvers=2 .
-To mount via NFS version 3, use the
-.BR nfs
-file system type and specify
-.BR nfsvers=3 .
-Version 3 is the default protocol version for the
-.BR nfs
-file system type when
-.BR nfsvers=
-is not specified on the mount command and both client and server
-support it.
-To mount via NFS version 4, use the
-.BR nfs4
-file system type.
The
-.BR nfsvers=
-keyword is not supported for the
-.BR nfs4
-file system type.
+.BR mount (8)
+command attaches a file system to the system's
+name space hierarchy at a given mount point.
+The
+.I /etc/fstab
+file describes how
+.BR mount (8)
+should assemble a system's file name hierarchy
+from various independent file systems
+(including file systems exported by NFS servers).
+Each line in the
+.I /etc/fstab
+file describes a single file system, its mount point,
+and a set of default mount options for that mount point.
.P
-These file system types share similar mount options;
-the differences are listed below.
+For NFS file system mounts, a line in the
+.I /etc/fstab
+file specifies the server name,
+the path name of the exported server directory to mount,
+the local directory that is the mount point,
+the type of file system that is being mounted,
+and a list of mount options that control
+the way the filesystem is mounted and
+how the NFS client behaves when accessing
+files on this mount point.
+The fifth and sixth fields on each line are not used
+by NFS, thus conventionally each contain the digit zero. For example:
.P
-Here is an example from an \fI/etc/fstab\fP file for an NFSv3 mount
-over TCP.
-.sp
-.nf
-.ta 2.5i +0.75i +0.75i +1.0i
-server:/usr/local/pub /pub nfs rsize=32768,wsize=32768,timeo=14,intr
-.fi
+.SP
+.NF
+.TA 2.5i +0.75i +0.75i +1.0i
+ server:path /mountpoint fstype option,option,... 0 0
+.FI
.P
-Here is an example for an NFSv4 mount over TCP using Kerberos
-5 mutual authentication.
-.sp
-.nf
-.ta 2.5i +0.75i +0.75i +1.0i
-server:/usr/local/pub /pub nfs4 proto=tcp,sec=krb5,hard,intr
-.fi
+The server's hostname and export pathname
+are separated by a colon, while
+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,
+or a dotted quad IPv4 address.
+The
+.I fstype
+field contains either "nfs" (for version 2 or version 3 NFS mounts)
+or "nfs4" (for NFS version 4 mounts).
+The
+.B nfs
+and
+.B nfs4
+file system types share similar mount options,
+which are described below.
+.SH "MOUNT OPTIONS"
+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
+.B defaults
+in
+.IR /etc/fstab .
+.
.DT
-.SS Options for the nfs file system type
-.TP 1.5i
-.I rsize=n
-The number of bytes NFS uses when reading files from an NFS server.
-The rsize is negotiated between the server and client to determine
-the largest block size that both can support.
-The value specified by this option is the maximum size that could
-be used; however, the actual size used may be smaller.
-Note: Setting this size to a value less than the largest supported
-block size will adversely affect performance.
-.TP 1.5i
-.I wsize=n
-The number of bytes NFS uses when writing files to an NFS server.
-The wsize is negotiated between the server and client to determine
-the largest block size that both can support.
-The value specified by this option is the maximum size that could
-be used; however, the actual size used may be smaller.
-Note: Setting this size to a value less than the largest supported
-block size will adversely affect performance.
-.TP 1.5i
-.I timeo=n
-The value in tenths of a second before sending the
-first retransmission after an RPC timeout.
-The default value is 7 tenths of a second. After the first timeout,
-the timeout is doubled after each successive timeout until a maximum
-timeout of 60 seconds is reached or the enough retransmissions
-have occured to cause a major timeout. Then, if the filesystem
-is hard mounted, each new timeout cascade restarts at twice the
-initial value of the previous cascade, again doubling at each
-retransmission. The maximum timeout is always 60 seconds.
-Better overall performance may be achieved by increasing the
-timeout when mounting on a busy network, to a slow server, or through
-several routers or gateways.
-.TP 1.5i
-.I retrans=n
-The number of minor timeouts and retransmissions that must occur before
-a major timeout occurs. The default is 3 timeouts. When a major timeout
-occurs, the file operation is either aborted or a "server not responding"
-message is printed on the console.
-.TP 1.5i
-.I acregmin=n
-The minimum time in seconds that attributes of a regular file should
-be cached before requesting fresh information from a server.
-The default is 3 seconds.
-.TP 1.5i
-.I acregmax=n
-The maximum time in seconds that attributes of a regular file can
-be cached before requesting fresh information from a server.
-The default is 60 seconds.
-.TP 1.5i
-.I acdirmin=n
-The minimum time in seconds that attributes of a directory should
-be cached before requesting fresh information from a server.
-The default is 30 seconds.
-.TP 1.5i
-.I acdirmax=n
-The maximum time in seconds that attributes of a directory can
-be cached before requesting fresh information from a server.
-The default is 60 seconds.
-.TP 1.5i
-.I actimeo=n
-Using actimeo sets all of
-.I acregmin,
-.I acregmax,
-.I acdirmin,
+.SS "Valid options for either the nfs or nfs4 file system type"
+These options are valid to use when mounting either
+.B nfs
+or
+.B nfs4
+file system types.
+They imply the same behavior
+and have the same default for both file system types.
+.TP 1.5i
+.BR soft " / " hard
+Determines the recovery behavior of the NFS client
+after an NFS request times out.
+If neither option is specified (or if the
+.B hard
+option is specified), NFS requests are retried indefinitely.
+If the
+.B soft
+option is specified, then the NFS client fails an NFS request
+after
+.B retrans
+retransmissions have been sent,
+causing the NFS client to return an error
+to the calling application.
+.IP
+.I NB:
+A so-called "soft" timeout can cause
+silent data corruption in certain cases. As such, use the
+.B soft
+option only when client responsiveness
+is more important than data integrity.
+Using NFS over TCP or increasing the value of the
+.B retrans
+option may mitigate some of the risks of using the
+.B soft
+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
+option is not specified, requests are retried after
+60 seconds for NFS over TCP, and are retried after 7/10 of a second for
+NFS over UDP.
+.IP
+For NFS over TCP, the client uses a fixed timeout, as specified by the
+.B timeo
+option. 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
+.B timeo
+setting for infrequently used request types (such as FSINFO requests).
+After each retransmission, the NFS client doubles the timeout for that
+request, up to a maximum timeout length of 60 seconds.
+.TP 1.5i
+.BI retrans= n
+The number of times the NFS client retries a request before
+it attempts further recovery action. If the
+.B retrans
+option is not specified, the NFS client retries each request
+three times.
+.IP
+The NFS client generates a "server not responding" message
+after
+.B retrans
+retries, then attempts further recovery (depending on whether the
+.B hard
+mount option is in effect).
+.TP 1.5i
+.BI 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
+.B rsize
+setting. The largest read payload supported by the Linux NFS client
+is 1,048,576 bytes (one megabyte).
+.IP
+The
+.B rsize
+value is a positive integral multiple of 1024.
+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
+multiple of 1024.
+.IP
+If an
+.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.
+.IP
+The
+.B rsize
+mount option as specified on the
+.BR mount (8)
+command line appears in the
+.I /etc/mtab
+file. However, the effective
+.B rsize
+value negotiated by the client and server is reported in the
+.I /proc/mounts
+file.
+.TP 1.5i
+.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
+NFS WRITE request is equal to
+or smaller than the
+.B wsize
+setting. The largest write payload supported by the Linux NFS client
+is 1,048,576 bytes (one megabyte).
+.IP
+Similar to
+.B rsize
+, the
+.B wsize
+value is a positive integral multiple of 1024.
+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
+multiple of 1024.
+.IP
+If a
+.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
+value that they can both support.
+.IP
+The
+.B wsize
+mount option as specified on the
+.BR mount (8)
+command line appears in the
+.I /etc/mtab
+file. However, the effective
+.B wsize
+value negotiated by the client and server is reported in the
+.I /proc/mounts
+file.
+.TP 1.5i
+.BR ac " / " noac
+Selects whether the client may cache file attributes. If neither
+option is specified (or if
+.B ac
+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
+.B noac
+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
+.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
+writes when they check the file's attributes.
+.IP
+Using the
+.B 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.
+.TP 1.5i
+.BI 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.
+.TP 1.5i
+.BI 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.
+.TP 1.5i
+.BI 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.
+.TP 1.5i
+.BI 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.
+.TP 1.5i
+.BI actimeo= n
+Using
+.B actimeo
+sets all of
+.BR acregmin ,
+.BR acregmax ,
+.BR acdirmin ,
and
-.I acdirmax
+.B acdirmax
to the same value.
-There is no default value.
+If this option is not specified, the NFS client uses
+the defaults for each of these options listed above.
.TP 1.5i
-.I retry=n
-The number of minutes to retry an NFS mount operation
+.BR bg " / " fg
+Determines how the
+.BR mount (8)
+command behaves if an attempt to mount an export fails.
+The
+.B fg
+option causes
+.BR 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
+.B fg
+nor
+.B bg
+mount option is specified.
+.IP
+If the
+.B bg
+option is specified, a timeout or failure causes the
+.BR 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.
+.IP
+If the local mount point directory is missing, the
+.BR mount (8)
+command acts as if the mount request timed out.
+This permits nested NFS mounts specified in
+.I /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
+.BR automount (8)
+for details).
+.TP 1.5i
+.BI retry= n
+The number of minutes that the
+.BR mount (8)
+command retries an NFS mount operation
in the foreground or background before giving up.
-The default value for forground mounts is 2 minutes.
-The default value for background mounts is 10000 minutes,
-which is roughly one week.
-.TP 1.5i
-.I namlen=n
-When an NFS server does not support version two of the
-RPC mount protocol, this option can be used to specify
-the maximum length of a filename that is supported on
-the remote filesystem. This is used to support the
-POSIX pathconf functions. The default is 255 characters.
-.TP 1.5i
-.I port=n
-The numeric value of the port to connect to the NFS server on.
-If the port number is 0 (the default) then query the
-remote host's portmapper for the port number to use.
-If the remote host's NFS daemon is not registered with
-its portmapper, the standard NFS port number 2049 is
-used instead.
-.TP 1.5i
-.I mountport=n
-The numeric value of the
-.B mountd
-port.
-.TP 1.5i
-.I mounthost=name
-The name of the host running
-.B mountd .
-.TP 1.5i
-.I mountprog=n
-Use an alternate RPC program number to contact the
-mount daemon on the remote host. This option is useful
-for hosts that can run multiple NFS servers.
-The default value is 100005 which is the standard RPC
-mount daemon program number.
-.TP 1.5i
-.I mountvers=n
-Use an alternate RPC version number to contact the
-mount daemon on the remote host. This option is useful
-for hosts that can run multiple NFS servers.
-The default value depends on which kernel you are using.
-.TP 1.5i
-.I nfsprog=n
-Use an alternate RPC program number to contact the
-NFS daemon on the remote host. This option is useful
-for hosts that can run multiple NFS servers.
-The default value is 100003 which is the standard RPC
-NFS daemon program number.
-.TP 1.5i
-.I nfsvers=n
-Use an alternate RPC version number to contact the
-NFS daemon on the remote host. This option is useful
-for hosts that can run multiple NFS servers.
-The default value depends on which kernel you are using.
-.TP 1.5i
-.I vers=n
-vers is an alternative to nfsvers and is compatible with
-many other operating systems.
-.TP 1.5i
-.I nolock
-Disable NFS locking. Do not start lockd.
-This is appropriate for mounting the root filesystem or
-.B /usr
-or
-.BR /var .
-These filesystems are typically either read-only or not shared, and in
-those cases, remote locking is not needed.
-This also needs to be used with some old NFS servers
-that don't support locking.
-.br
-Note that applications can still get locks on files, but the locks
-only provide exclusion locally. Other clients mounting the same
-filesystem will not be able to detect the locks.
-.TP 1.5i
-.I bg
-If the first NFS mount attempt times out, retry the mount
-in the background.
-After a mount operation is backgrounded, all subsequent mounts
-on the same NFS server will be backgrounded immediately, without
-first attempting the mount.
-A missing mount point is treated as a timeout,
-to allow for nested NFS mounts.
-.TP 1.5i
-.I fg
-If the first NFS mount attempt times out, retry the mount
-in the foreground.
-This is the complement of the
-.I bg
-option, and also the default behavior.
-.TP 1.5i
-.I soft
-If an NFS file operation has a major timeout then report an I/O error to
-the calling program.
-The default is to continue retrying NFS file operations indefinitely.
-.TP 1.5i
-.I hard
-If an NFS file operation has a major timeout then report
-"server not responding" on the console and continue retrying indefinitely.
-This is the default.
-.TP 1.5i
-.I intr
-If an NFS file operation has a major timeout and it is hard mounted,
-then allow signals to interupt the file operation and cause it to
-return EINTR to the calling program. The default is to not
-allow file operations to be interrupted.
-.TP 1.5i
-.I posix
-Mount the NFS filesystem using POSIX semantics. This allows
-an NFS filesystem to properly support the POSIX pathconf
-command by querying the mount server for the maximum length
-of a filename. To do this, the remote host must support version
-two of the RPC mount protocol. Many NFS servers support only
-version one.
-.TP 1.5i
-.I nocto
-Suppress the retrieval of new attributes when creating a file.
-.TP 1.5i
-.I noac
-Disable all forms of attribute caching entirely. This extracts a
-significant performance penalty but it allows two different NFS clients
-to get reasonable results when both clients are actively
-writing to a common export on the server.
-.TP 1.5i
-.I noacl
-Disables Access Control List (ACL) processing.
-.TP 1.5i
-.I sec=mode
-Set the security flavor for this mount to "mode".
-The default setting is \f3sec=sys\f1, which uses local
-unix uids and gids to authenticate NFS operations (AUTH_SYS).
-Other currently supported settings are:
-\f3sec=krb5\f1, which uses Kerberos V5 instead of local unix uids
-and gids to authenticate users;
-\f3sec=krb5i\f1, which uses Kerberos V5 for user authentication
-and performs integrity checking of NFS operations using secure
-checksums to prevent data tampering; and
-\f3sec=krb5p\f1, which uses Kerberos V5 for user authentication
-and integrity checking, and encrypts NFS traffic to prevent
-traffic sniffing (this is the most secure setting).
-Note that there is a performance penalty when using integrity
-or privacy.
-.TP 1.5i
-.I tcp
-Mount the NFS filesystem using the TCP protocol. This is the default
-if it is supported by both client and server. Many NFS servers only
-support UDP.
-.TP 1.5i
-.I udp
-Mount the NFS filesystem using the UDP protocol.
-.TP 1.5i
-.I nordirplus
-Disables NFSv3 READDIRPLUS RPCs. Use this option when
-mounting servers that don't support or have broken
-READDIRPLUS implementations.
-.TP 1.5i
-.I nosharecache
-As of kernel 2.6.18, it is no longer possible to mount the same
-same filesystem with different mount options to a new mountpoint.
-It was deemed unsafe to do so, since cached data cannot be shared
-between the two mountpoints. In consequence, files or directories
-that were common to both mountpoint subtrees could often be seen to
-be out of sync following an update.
-.br
-This option allows administrators to select the pre-2.6.18 behaviour,
-permitting the same filesystem to be mounted with different mount
-options.
-.br
-.B Beware:
-Use of this option is not recommended unless you are certain that there
-are no hard links or subtrees of this mountpoint that are mounted
-elsewhere.
-.P
-All of the non-value options have corresponding nooption forms.
-For example, nointr means don't allow file operations to be
-interrupted.
-.SS Options for the nfs4 file system type
-.TP 1.5i
-.I rsize=n
-The number of bytes nfs4 uses when reading files from the server.
-The rsize is negotiated between the server and client to determine
-the largest block size that both can support.
-The value specified by this option is the maximum size that could
-be used; however, the actual size used may be smaller.
-Note: Setting this size to a value less than the largest supported
-block size will adversely affect performance.
-.TP 1.5i
-.I wsize=n
-The number of bytes nfs4 uses when writing files to the server.
-The wsize is negotiated between the server and client to determine
-the largest block size that both can support.
-The value specified by this option is the maximum size that could
-be used; however, the actual size used may be smaller.
-Note: Setting this size to a value less than the largest supported
-block size will adversely affect performance.
-.TP 1.5i
-.I timeo=n
-The value in tenths of a second before sending the
-first retransmission after an RPC timeout.
-The default value depends on whether
-.IR proto=udp
-or
-.IR proto=tcp
-is in effect (see below).
-The default value for UDP is 7 tenths of a second.
-The default value for TCP is 60 seconds.
-After the first timeout,
-the timeout is doubled after each successive timeout until a maximum
-timeout of 60 seconds is reached or the enough retransmissions
-have occured to cause a major timeout. Then, if the filesystem
-is hard mounted, each new timeout cascade restarts at twice the
-initial value of the previous cascade, again doubling at each
-retransmission. The maximum timeout is always 60 seconds.
-.TP 1.5i
-.I retrans=n
-The number of minor timeouts and retransmissions that must occur before
-a major timeout occurs. The default is 5 timeouts for
-.IR proto=udp
-and 2 timeouts for
-.IR proto=tcp .
-When a major timeout
-occurs, the file operation is either aborted or a "server not responding"
-message is printed on the console.
-.TP 1.5i
-.I acregmin=n
-The minimum time in seconds that attributes of a regular file should
-be cached before requesting fresh information from a server.
-The default is 3 seconds.
-.TP 1.5i
-.I acregmax=n
-The maximum time in seconds that attributes of a regular file can
-be cached before requesting fresh information from a server.
-The default is 60 seconds.
-.TP 1.5i
-.I acdirmin=n
-The minimum time in seconds that attributes of a directory should
-be cached before requesting fresh information from a server.
-The default is 30 seconds.
-.TP 1.5i
-.I acdirmax=n
-The maximum time in seconds that attributes of a directory can
-be cached before requesting fresh information from a server.
-The default is 60 seconds.
-.TP 1.5i
-.I actimeo=n
-Using actimeo sets all of
-.I acregmin,
-.I acregmax,
-.I acdirmin,
+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).
+.TP 1.5i
+.BI sec= mode
+The RPCGSS security flavor to use for accessing files on this mount point.
+If the
+.B sec
+option is not specified, or if
+.B sec=sys
+is specified, the NFS client uses the AUTH_SYS security flavor
+for all NFS requests on this mount point.
+Valid security flavors are
+.BR none ,
+.BR sys ,
+.BR krb5 ,
+.BR krb5i ,
+.BR krb5p ,
+.BR lkey ,
+.BR lkeyi ,
+.BR lkeyp ,
+.BR spkm ,
+.BR spkmi ,
and
-.I acdirmax
-to the same value.
-There is no default value.
+.BR spkmp .
+Refer to the SECURITY CONSIDERATIONS section for details.
.TP 1.5i
-.I retry=n
-The number of minutes to retry an NFS mount operation
-in the foreground or background before giving up.
-The default value for forground mounts is 2 minutes.
-The default value for background mounts is 10000 minutes,
-which is roughly one week.
-.TP 1.5i
-.I port=n
-The numeric value of the port to connect to the NFS server on.
-If the port number is 0 (the default) then query the
-remote host's portmapper for the port number to use.
-If the remote host's NFS daemon is not registered with
-its portmapper, the standard NFS port number 2049 is
-used instead.
-.TP 1.5i
-.I proto=n
-Mount the NFS filesystem using a specific network protocol
-instead of the default UDP protocol.
-Many NFS version 4 servers only support TCP.
-Valid protocol types are
-.IR udp
+.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
+accessed via different mount points.
+.IP
+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
+.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
+point take effect for subsequent concurrent mounts of the same export.
+.IP
+As of kernel 2.6.18, the behavior specified by
+.B 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.
+.SS "Valid options for the nfs file system type"
+Use these options, along with the options in the above subsection,
+for mounting the
+.B nfs
+file system type.
+.TP 1.5i
+.BI proto= netid
+The transport protocol used by the NFS client
+to transmit requests to the NFS server for this mount point.
+.I netid
+can be either
+.B udp
+or
+.BR tcp .
+Each transport protocol uses different default
+.B retrans
and
-.IR tcp .
+.B timeo
+settings; refer to the description of these two mount options for details.
+.IP
+In addition to controlling how the NFS client transmits requests to
+the server, this mount option also controls how the
+.BR mount (8)
+command communicates with the server's rpcbind and mountd services.
+Specifying
+.B proto=tcp
+forces all traffic from the
+.BR mount (8)
+command and the NFS client to use TCP.
+Specifying
+.B proto=udp
+forces all traffic types to use UDP.
+.IP
+If the
+.B proto
+mount option is not specified, the
+.BR 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.
.TP 1.5i
-.I clientaddr=n.n.n.n
-Specifies a single IPv4 address in dotted-quad form that
-the NFS client advertises to allow servers to perform
-NFSv4 callback requests against files on this mount point.
-If the server is not able to establish callback connections
-to clients, performance may degrade, or accesses to
-files may temporarily hang.
+.B udp
+The
+.B udp
+option is an alternative to specifying
+.BR proto=udp.
+It is included for compatibility with other operating systems.
+.TP 1.5i
+.B tcp
+The
+.B tcp
+option is an alternative to specifying
+.BR proto=tcp.
+It is included for compatibility with other operating systems.
+.TP 1.5i
+.BI 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.
+.IP
+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.
+.TP 1.5i
+.BI 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.
+.IP
+If this option is not specified,
+or if the specified port value is 0, then the
+.BR 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.
.IP
+This option can be used when mounting an NFS server
+through a firewall that blocks the rpcbind protocol.
+.TP 1.5i
+.BI mounthost= name
+The hostname of the host running mountd.
If this option is not specified, the
.BR mount (8)
-command attempts to discover an appropriate callback
-address automatically.
+command assumes that the mountd service runs
+on the same host as the NFS service.
+.TP 1.5i
+.BI 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.
+.TP 1.5i
+.BI 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.
+.IP
+Some early versions of NFS did not support this negotiation.
+Using this option ensures that
+.BR pathconf (3)
+reports the proper maximum component length to applications
+in such cases.
+.TP 1.5i
+.BI nfsvers= n
+The NFS protocol version number used to contact the server's NFS service.
+The Linux client supports version 2 and version 3 of the NFS protocol
+when using the file system type
+.BR nfs .
+If the server does not support the requested version,
+the mount request fails.
+If this option is not specified, the client attempts to use version 3,
+but negotiates the NFS version with the server if version 3 support
+is not available.
+.TP 1.5i
+.BI vers= n
+This option is an alternative to the
+.B nfsvers
+option.
+It is included for compatibility with other operating systems.
+.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.
+When using the
+.B 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.
+.IP
+NLM locking must be disabled with the
+.B nolock
+option when using NFS to mount
+.I /var
+because
+.I /var
+contains files used by the NLM implementation on Linux.
+Using the
+.B nolock
+option is also required when mounting exports on NFS servers
+that do not support the NLM protocol.
+.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 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
+a signal.
+.IP
+Using the
+.B intr
+option is preferred to using the
+.B soft
+option because it is significantly less likely to result in data corruption.
+.TP 1.5i
+.BR cto " / " nocto
+Selects whether to use close-to-open cache coherence semantics.
+If neither option is specified (or if
+.B cto
+is specified), the client uses close-to-open
+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.
+.IP
+Using the
+.B 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.
+.TP 1.5i
+.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
+made a standard part of the NFS protocol specification.
+.IP
+If neither
+.B acl
+nor
+.B 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.
+.TP 1.5i
+.BR rdirplus " / " nordirplus
+Selects whether to use NFS version 3 READDIRPLUS requests.
+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.
+.SS "Valid options for the nfs4 file system type"
+Use these options, along with the options in the first subsection above,
+for mounting the
+.B nfs4
+file system type.
+.TP 1.5i
+.BI proto= netid
+The transport protocol used by the NFS client
+to transmit requests to the NFS server for this mount point.
+.I netid
+can be either
+.B udp
+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.
+Refer to the TRANSPORT METHODS section for more details.
+.TP 1.5i
+.BI 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.
+.IP
+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.
+.IP
+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.
+.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
+.B nointr
+is specified, signals do not
+interrupt NFS operations.
+.IP
+Using the
+.B intr
+option is preferred to using the
+.B soft
+option because it is significantly less likely to result in data corruption.
+.TP 1.5i
+.BR cto " / " nocto
+Selects whether to use close-to-open cache coherence semantics
+for NFS directories on this mount point.
+If neither
+.B cto
+nor
+.B nocto
+is specified,
+the default is to use close-to-open cache coherence
+semantics for directories.
+.IP
+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.
+.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
+may degrade, or accesses to files may temporarily hang.
+.IP
+If this option is not specified, the
+.BR 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,
-and should be explicitly set using this mount option.
-.TP 1.5i
-.I sec=mode
-Same as \f3sec=mode\f1 for the nfs filesystem type (see above).
-.TP 1.5i
-.I bg
-If an NFS mount attempt times out, retry the mount
-in the background.
-After a mount operation is backgrounded, all subsequent mounts
-on the same NFS server will be backgrounded immediately, without
-first attempting the mount.
-A missing mount point is treated as a timeout,
-to allow for nested NFS mounts.
-.TP 1.5i
-.I fg
-If the first NFS mount attempt times out, retry the mount
-in the foreground.
-This is the complement of the
-.I bg
-option, and also the default behavior.
-.TP 1.5i
-.I soft
-If an NFS file operation has a major timeout then report an I/O error to
-the calling program.
-The default is to continue retrying NFS file operations indefinitely.
-.TP 1.5i
-.I hard
-If an NFS file operation has a major timeout then report
-"server not responding" on the console and continue retrying indefinitely.
-This is the default.
-.TP 1.5i
-.I intr
-If an NFS file operation has a major timeout and it is hard mounted,
-then allow signals to interupt the file operation and cause it to
-return EINTR to the calling program. The default is to not
-allow file operations to be interrupted.
-.TP 1.5i
-.I nocto
-Suppress the retrieval of new attributes when creating a file.
-.TP 1.5i
-.I noac
-Disable attribute caching, and force synchronous writes.
-This extracts a
-server performance penalty but it allows two different NFS clients
-to get reasonable good results when both clients are actively
-writing to common filesystem on the server.
-.TP 1.5i
-.I nosharecache
-As of kernel 2.6.18, it is no longer possible to mount the same
-same filesystem with different mount options to a new mountpoint.
-It was deemed unsafe to do so, since cached data cannot be shared
-between the two mountpoints. In consequence, files or directories
-that were common to both mountpoint subtrees could often be seen to
-be out of sync following an update.
-.br
-This option allows administrators to select the pre-2.6.18 behaviour,
-permitting the same filesystem to be mounted with different mount
-options.
-.br
-.B Beware:
-Use of this option is not recommended unless you are certain that there
-are no hard links or subtrees of this mountpoint that are mounted
-elsewhere.
-.P
-All of the non-value options have corresponding nooption forms.
-For example, nointr means don't allow file operations to be
-interrupted.
+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.
+.SH EXAMPLES
+To mount an export using NFS version 2,
+use the
+.B nfs
+file system type and specify the
+.B nfsvers=2
+mount option.
+To mount using NFS version 3,
+use the
+.B nfs
+file system type and specify the
+.B nfsvers=3
+mount option.
+To mount using NFS version 4,
+use the
+.B nfs4
+file system type.
+The
+.B nfsvers
+mount option is not supported for the
+.B nfs4
+file system type.
+.P
+The following example from an
+.I /etc/fstab
+file causes the mount command to negotiate
+reasonable defaults for NFS behavior.
+.P
+.NF
+.TA 2.5i +0.7i +0.7i +.7i
+ server:/export /mnt nfs defaults 0 0
+.FI
+.P
+Here is an example from an /etc/fstab file for an NFS version 2 mount over UDP.
+.P
+.NF
+.TA 2.5i +0.7i +0.7i +.7i
+ server:/export /mnt nfs nfsvers=2,proto=udp 0 0
+.FI
+.P
+Try this example to mount using NFS version 4 over TCP
+with Kerberos 5 mutual authentication.
+.P
+.NF
+.TA 2.5i +0.7i +0.7i +.7i
+ server:/export /mnt nfs4 sec=krb5 0 0
+.FI
+.P
+This example can be used to mount /usr over NFS.
+.P
+.NF
+.TA 2.5i +0.7i +0.7i +.7i
+ server:/export /usr nfs ro,nolock,nocto,actimeo=3600 0 0
+.FI
+.SH "TRANSPORT METHODS"
+NFS clients send requests to NFS servers via
+Remote Procedure Calls, or
+.IR RPCs .
+The RPC client discovers remote service endpoints automatically,
+handles per-request authentication,
+adjusts request parameters for different byte endianness on client and server,
+and retransmits requests that may have been lost by the network or server.
+RPC requests and replies flow over a network transport.
+.P
+In most cases, the
+.BR mount (8)
+command, NFS client, and NFS server
+can automatically negotiate proper transport
+and data transfer size settings for a mount point.
+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
+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
+an entire large read or write request.
+.P
+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
+requirement for mounting a server through a network firewall.
+.P
+Under normal circumstances, networks drop packets much more
+frequently than NFS servers drop requests. As such, an aggressive
+retransmit timeout setting for NFS over TCP is unnecessary. Typical
+timeout settings for NFS over TCP are between one and ten minutes.
+After the client exhausts its retransmits (the value of the
+.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,
+.B rsize
+and
+.B wsize
+can safely be allowed to default to the largest values supported by
+both client and server, independent of the network's MTU size.
+.SH "DATA AND METADATA COHERENCE"
+Some modern cluster file systems provide
+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,
+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.
+.DT
+.SS "Close-to-open cache consistency"
+When an application opens a file stored on an NFS server,
+the NFS client checks that it still exists on the server
+and is permitted to the opener by sending a GETATTR or ACCESS request.
+When the application closes the file,
+the NFS client writes back any pending changes
+to the file so that the next opener can view the changes.
+This also gives the NFS client an opportunity to report
+any server write errors to the application
+via the return code from
+.BR close (2).
+The behavior of checking at open time and flushing at close time
+is referred to as close-to-open cache consistency.
+.SS "Weak cache consistency"
+There are still opportunities for a client's data cache
+to contain stale data.
+The NFS version 3 protocol introduced "weak cache consistency"
+(also known as WCC) which provides a way of efficiently checking
+a file's attributes before and after a single request.
+This allows a client to help identify changes
+that could have been made by other clients.
+.P
+When a client is using many concurrent operations
+that update the same file at the same time
+(for example, during asynchronous write behind),
+it is still difficult to tell whether it was
+that client's updates or some other client's updates
+that altered the file.
+.SS "Attribute caching"
+Use the
+.B noac
+mount option to achieve attribute cache coherence
+among multiple clients.
+Almost every file system operation checks
+file attribute information.
+The client keeps this information cached
+for a period of time to reduce network and server load.
+When
+.B noac
+is in effect, a client's file attribute cache is disabled,
+so each operation that needs to check a file's attributes
+is forced to go back to the server.
+This permits a client to see changes to a file very quickly,
+at the cost of many extra network operations.
+.P
+Be careful not to confuse the
+.B noac
+option with "no data caching."
+The
+.B noac
+mount option prevents the client from caching file metadata,
+but there are still races that may result in data cache incoherence
+between client and server.
+.P
+The NFS protocol is not designed to support
+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
+can also open their files with the O_DIRECT flag
+to disable data caching entirely.
+.SS "The sync mount option"
+The NFS client treats the
+.B sync
+mount option differently than some other file systems
+(refer to
+.BR mount (8)
+for a description of the generic
+.B sync
+and
+.B async
+mount options).
+If neither
+.B sync
+nor
+.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:
+.IP
+Memory pressure forces reclamation of system memory resources.
+.IP
+An application flushes file data explicitly with
+.BR sync (2),
+.BR msync (2),
+or
+.BR fsync (3).
+.IP
+An application closes a file with
+.BR close (2).
+.IP
+The file is locked/unlocked via
+.BR fcntl (2).
+.P
+In other words, under normal circumstances,
+data written by an application may not immediately appear
+on the server that hosts the file.
+.P
+If the
+.B sync
+option is specified on a mount point,
+any system call that writes data to files on that mount point
+causes that data to be flushed to the server
+before the system call returns control to user space.
+This provides greater data cache coherence among clients,
+but at a significant performance cost.
+.P
+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
+mount option.
+.SS "Using file locks with NFS"
+The Network Lock Manager protocol is a separate sideband protocol
+used to manage file locks in NFS version 2 and version 3.
+To support lock recovery after a client or server reboot,
+a second sideband protocol --
+known as the Network Status Manager protocol --
+is also required.
+In NFS version 4,
+file locking is supported directly in the main NFS protocol,
+and the NLM and NSM sideband protocols are not used.
+.P
+In most cases, NLM and NSM services are started automatically,
+and no extra configuration is required.
+Configure all NFS clients with fully-qualified domain names
+to ensure that NFS servers can find clients to notify them of server reboots.
+.P
+NLM supports advisory file locks only.
+To lock NFS files, use
+.BR fcntl (2)
+with the F_GETLK and F_SETLK commands.
+The NFS client converts file locks obtained via
+.BR flock (2)
+to advisory locks.
+.P
+When mounting servers that do not support the NLM protocol,
+or when mounting an NFS server through a firewall
+that blocks the NLM service port,
+specify the
+.B nolock
+mount option. NLM locking must be disabled with the
+.B nolock
+option when using NFS to mount
+.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.
+.SS "NFS version 4 caching features"
+The data and metadata caching behavior of NFS version 4
+clients is similar to that of earlier versions.
+However, NFS version 4 adds two features that improve
+cache behavior:
+.I change attributes
+and
+.IR "file delegation" .
+.P
+The
+.I change attribute
+is a new part of NFS file and directory metadata
+which tracks data changes.
+It replaces the use of a file's modification
+and change time stamps
+as a way for clients to validate the content
+of their caches.
+Change attributes are independent of the time stamp
+resolution on either the server or client, however.
+.P
+A
+.I file delegation
+is a contract between an NFS version 4 client
+and server that allows the client to treat a file temporarily
+as if no other client is accessing it.
+The server promises to notify the client (via a callback request) if another client
+attempts to access that file.
+Once a file has been delegated to a client, the client can
+cache that file's data and metadata aggressively without
+contacting the server.
+.P
+File delegations come in two flavors:
+.I read
+and
+.IR write .
+A
+.I read
+delegation means that the server notifies the client
+about any other clients that want to write to the file.
+A
+.I write
+delegation means that the client gets notified about
+either read or write accessors.
+.P
+Servers grant file delegations when a file is opened,
+and can recall delegations at any time when another
+client wants access to the file that conflicts with
+any delegations already granted.
+Delegations on directories are not supported.
+.P
+In order to support delegation callback, the server
+checks the network return path to the client during
+the client's initial contact with the server.
+If contact with the client cannot be established,
+the server simply does not grant any delegations to
+that client.
+.SH "SECURITY CONSIDERATIONS"
+NFS servers control access to file data,
+but they depend on their RPC implementation
+to provide authentication of NFS requests.
+Traditional NFS access control mimics
+the standard mode bit access control provided in local file systems.
+Traditional RPC authentication uses a number
+to represent each user
+(usually the user's own uid),
+a number to represent the user's group (the user's gid),
+and a set of up to 16 auxiliary group numbers
+to represent other groups of which the user may be a member.
+.P
+Typically, file data and user ID values appear unencrypted
+(i.e. "in the clear") on the network.
+Moreover, NFS versions 2 and 3 use
+separate sideband protocols for mounting,
+locking and unlocking files,
+and reporting system status of clients and servers.
+These auxiliary protocols use no authentication.
+.P
+In addition to combining these sideband protocols with the main NFS protocol,
+NFS version 4 introduces more advanced forms of access control,
+authentication, and in-transit data protection.
+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
+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.
+RPCGSS authentication can also be used with NFS versions 2 and 3,
+but does not protect their sideband protocols.
+.P
+The
+.B sec
+mount option specifies the RPCGSS security mode
+that is in effect on a given NFS mount point.
+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
+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
+.BR rpc.gssd (8)
+man page for details.
+.P
+Two additional flavors of Kerberos security are supported:
+.B krb5i
+and
+.BR krb5p .
+The
+.B krb5i
+security flavor provides a cryptographically strong guarantee
+that the data in each RPC request has not been tampered with.
+The
+.B krb5p
+security flavor encrypts every RPC request
+to prevent data exposure during network transit; however,
+expect some performance impact
+when using integrity checking or encryption.
+Similar support for other forms of cryptographic security (such as lipkey and SPKM3)
+is also available.
+.P
+The NFS version 4 protocol allows
+clients and servers to negotiate among multiple security flavors
+during mount processing.
+However, Linux does not yet implement such negotiation.
+The Linux client specifies a single security flavor at mount time
+which remains in effect for the lifetime of the mount.
+If the server does not support this flavor,
+the initial mount request is rejected by the server.
+.SS "Mounting through a firewall"
+A firewall may reside between an NFS client and server,
+or the client or server may block some of its own ports via IP
+filter rules.
+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
+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:
+.IP
+What network port each RPC-based service is using
+.IP
+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),
+auxiliary services such as the NLM service can choose
+any unused port number at random.
+.P
+Common firewall configurations block the well-known rpcbind port.
+In the absense of an rpcbind service,
+the server administrator fixes the port number
+of NFS-related services so that the firewall
+can allow access to specific NFS service ports.
+Client administrators then specify the port number
+for the mountd service via the
+.BR mount (8)
+command's
+.B mountport
+option.
+It may also be necessary to enforce the use of TCP or UDP
+if the firewall blocks one of those transports.
+.SS "NFS Access Control Lists"
+Solaris allows NFS version 3 clients direct access
+to POSIX Access Control Lists stored in its local file systems.
+This proprietary sideband protocol, known as NFSACL,
+provides richer access control than mode bits.
+Linux implements this protocol
+for compatibility with the Solaris NFS implementation.
+The NFSACL protocol never became a standard part
+of the NFS version 3 specification, however.
+.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,
+some translation between the two is required
+in an environment that mixes POSIX ACLs and NFS version 4.
.SH FILES
+.TP 1.5i
.I /etc/fstab
-.SH "SEE ALSO"
-.BR fstab "(5), " mount "(8), " umount "(8), " exports (5)
-.SH AUTHOR
-"Rick Sladkey" <jrs@world.std.com>
+file system table
.SH BUGS
+The generic
+.B remount
+option is not fully supported.
+Generic options, such as
+.BR rw " and " ro
+can be modified using the
+.B remount
+option,
+but NFS-specific options are not all supported.
+The underlying transport or NFS version
+cannot be changed by a remount, for example.
+Performing a remount on an NFS file system mounted with the
+.B noac
+option may have unintended consequences.
+The
+.B noac
+option is a mixture of a generic option,
+.BR sync ,
+and an NFS-specific option
+.BR actimeo=0 .
.P
-Checking files on NFS filesystem referenced by file descriptors (i.e. the
-.BR fcntl
-and
-.BR ioctl
-families of functions) may lead to inconsistent result due to the lack of
-consistency check in kernel even if noac is used.
+Before 2.4.7, the Linux NFS client did not support NFS over TCP.
+.P
+Before 2.4.20, the Linux NFS client used a heuristic
+to determine whether cached file data was still valid
+rather than using the standard close-to-open cache coherency method
+described above.
+.P
+Starting with 2.4.22, the Linux NFS client employs
+a Van Jacobsen-based RTT estimator to determine retransmit
+timeout values when using NFS over UDP.
+.P
+Before 2.6.0, the Linux NFS client did not support NFS version 4.
+.P
+Before 2.6.8, the Linux NFS client used only synchronous reads and writes
+when the
+.BR rsize " and " wsize
+settings were smaller than the system's page size.
+.P
+The Linux NFS client does not yet support
+certain optional features of the NFS version 4 protocol,
+such as security negotiation, server referrals, and named attributes.
+.SH "SEE ALSO"
+.BR fstab (5),
+.BR mount (8),
+.BR umount (8),
+.BR mount.nfs (5),
+.BR umount.nfs (5),
+.BR exports (5),
+.BR nfsd (8),
+.BR rpc.idmapd (8),
+.BR rpc.gssd (8),
+.BR rpc.svcgssd (8),
+.BR kerberos (1)
+.sp
+RFC 768 for the UDP specification.
+.br
+RFC 793 for the TCP specification.
+.br
+RFC 1094 for the NFS version 2 specification.
+.br
+RFC 1813 for the NFS version 3 specification.
+.br
+RFC 1832 for the XDR specification.
+.br
+RFC 1833 for the RPC bind specification.
+.br
+RFC 2203 for the RPCSEC GSS API protocol specification.
+.br
+RFC 3530 for the NFS version 4 specification.
Reference in New Issue View Git Blame Copy Permalink