NFS(5)
NAME
nfs - nfs fstab format and options
SYNOPSIS
/etc/fstab
DESCRIPTION
The fstab file contains information about which filesys-
tems 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.
Here is an example from an /etc/fstab file from an NFS
mount.
server:/usr/local/pub /pub nfs rsize=8192,wsize=8192,timeo=14,intr
Options
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 rsize=8192.)
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 wsize=8192.)
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 sec-
onds is reached or the enough retransmis-
sions have occured to cause a major time-
out. 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 retransmis-
sion. 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 gate-
ways.
retrans=n The number of minor timeouts and retrans-
missions that must occur before a major
timeout occurs. The default is 3 timeouts.
When a major timeout occurs, the file oper-
ation is either aborted or a "server not
responding" message is printed on the con-
sole.
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.
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.
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.
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.
actimeo=n Using actimeo sets all of acregmin, acreg-
max, acdirmin, and acdirmax to the same
value. There is no default value.
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.
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.
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 regis-
tered with its portmapper, the standard NFS
port number 2049 is used instead.
mountport=n The numeric value of the mountd port.
mounthost=name The name of the host running mountd .
mountprog=n Use an alternate RPC program number to con-
tact 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.
mountvers=n Use an alternate RPC version number to con-
tact 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.
nfsprog=n Use an alternate RPC program number to con-
tact 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.
nfsvers=n Use an alternate RPC version number to con-
tact 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.
bg If the first NFS mount attempt times out,
retry the mount in the background. After a
mount operation is backgrounded, all subse-
quent 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.
fg If the first NFS mount attempt times out,
retry the mount in the foreground. This is
the complement of the bg option, and also
the default behavior.
soft If an NFS file operation has a major time-
out then report an I/O error to the calling
program. The default is to continue retry-
ing NFS file operations indefinitely.
hard If an NFS file operation has a major time-
out then report "server not responding" on
the console and continue retrying indefi-
nitely. This is the default.
intr If an NFS file operation has a major time-
out and it is hard mounted, then allow sig-
nals 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.
posix Mount the NFS filesystem using POSIX seman-
tics. This allows an NFS filesystem to
properly support the POSIX pathconf command
by querying the mount server for the maxi-
mum length of a filename. To do this, the
remote host must support version two of the
RPC mount protocol. Many NFS servers sup-
port only version one.
nocto Suppress the retrieval of new attributes
when creating a file.
noac Disable all forms of attribute caching
entirely. This extracts a server perfor-
mance 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.
tcp Mount the NFS filesystem using the TCP pro-
tocol instead of the default UDP protocol.
Many NFS severs only support UDP.
udp Mount the NFS filesystem using the UDP pro-
tocol. This is the default.
All of the non-value options have corresponding nooption
forms. For example, nointr means don't allow file opera-
tions to be interrupted.
FILES
/etc/fstab
SEE ALSO
fstab(5) mount(8) umount(8) exports(5)
AUTHOR
"Rick Sladkey" lt;jrs@world.std.com
BUGS
The posix, and nocto options are parsed by mount but cur-
rently are silently ignored.
The tcp and namlen options are implemented but are not
currently supported by the Linux kernel.
The umount command should notify the server when an NFS
filesystem is unmounted.