nfs.5

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.\" nfs.5 "Rick Sladkey" <[e-mail]>
.\" Wed Feb  8 12:52:42 1995, [e-mail]: updates for Ross Biro's
.\" patches. "
.TH NFS 5 "20 November 1993" "Linux 0.99" "Linux Programmer's Manual"
.SH NAME
nfs \- nfs 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
Here is an example from an \fI/etc/fstab\fP file from an NFS mount.
.sp
.nf
.ta 2.5i +0.75i +0.75i +1.0i
server:/usr/local/pub	/pub	nfs	rsize=8192,wsize=8192,timeo=14,intr
.fi
.DT
.SS Options
.TP 1.5i
.I rsize=n
The number of bytes NFS uses when reading files from an NFS server.
The default value is dependent on the kernel, currently 1024 bytes.
(However, throughput is improved greatly by asking for
.IR rsize=8192 .)
.TP 1.5i
.I wsize=n
The number of bytes NFS uses when writing files to an NFS server.
The default value is dependent on the kernel, currently 1024 bytes.
(However, throughput is improved greatly by asking for
.IR wsize=8192 .)
.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 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 is version 1.
.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 is version 2.
.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
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 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.
.SH FILES
.I /etc/fstab
.SH "SEE ALSO"
.BR fstab "(5), " mount "(8), " umount "(8), " exports (5)
.SH AUTHOR
"Rick Sladkey" <[e-mail]>
.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.