+.\" 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"
+.SH NAME
+nfs \- nfs and nfs4 fstab format and options
+.SH SYNOPSIS
+.B /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.
+.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 .
+Version 2 is the default protocol version for the
+.BR nfs
+file system type when
+.BR nfsvers=
+is not specified on the mount command.
+To mount via NFS version 3, use the
+.BR nfs
+file system type and specify
+.BR nfsvers=3 .
+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.
+.P
+These file system types share similar mount options;
+the differences are listed below.
+.P
+Here is an example from an \fI/etc/fstab\fP file for an NFSv2 mount
+over UDP.
+.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
+.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
+.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,
+and
+.I acdirmax
+to the same value.
+There is no default value.
+.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 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 has to be used with some old NFS servers
+that don't support locking.
+.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 instead of the
+default UDP protocol. Many NFS servers only support UDP.
+.TP 1.5i
+.I udp
+Mount the NFS filesystem using the UDP protocol. This
+is the default.
+.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,
+and
+.I acdirmax
+to the same value.
+There is no default value.
+.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
+and
+.IR tcp .
+.TP 1.5i
+.I clientaddr=n
+On a multi-homed client, this
+causes the client to use a specific callback address when
+communicating with an NFS version 4 server.
+This option is currently ignored.
+.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.
+.P
+All of the non-value options have corresponding nooption forms.
+For example, nointr means don't allow file operations to be
+interrupted.
+.SH FILES
+.I /etc/fstab
+.SH "SEE ALSO"
+.BR fstab "(5), " mount "(8), " umount "(8), " exports (5)
+.SH AUTHOR
+"Rick Sladkey" <jrs@world.std.com>
+.SH BUGS
+The posix, and nocto options are parsed by mount
+but currently are silently ignored.
+.P
+The tcp and namlen options are implemented but are not currently
+supported by the Linux kernel.
+.P
+The umount command should notify the server
+when an NFS filesystem is unmounted.
+.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.
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