NFS(5) Linux Programmer's Manual NFS(5)NAMEnfs - nfs and nfs4 fstab format and options
SYNOPSIS
/etc/fstab
DESCRIPTION
The 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.
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 nfs file system type and specify nfsvers=2.
Version 2 is the default protocol version for the nfs file system type
when nfsvers= is not specified on the mount command. To mount via NFS
version 3, use the nfs file system type and specify nfsvers=3. To
mount via NFS version 4, use the nfs4 file system type. The nfsvers=
keyword is not supported for the nfs4 file system type.
These file system types share similar mount options; the differences
are listed below.
Here is an example from an /etc/fstab file for an NFSv2 mount over UDP.
server:/usr/local/pub /pub nfs rsize=32768,wsize=32768,timeo=14,intr
Here is an example for an NFSv4 mount over TCP using Kerberos 5 mutual
authentication.
server:/usr/local/pub /pub nfs4 proto=tcp,sec=krb5,hard,intr
Options for the nfs file system type
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.
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.
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 time‐
out cascade restarts at twice the initial value of the
previous cascade, again doubling at each retransmission.
The maximum timeout is always 60 seconds. Better over‐
all performance may be achieved by increasing the time‐
out when mounting on a busy network, to a slow server,
or through several routers or gateways.
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.
acregmin=n The minimum time in seconds that attributes of a regular
file should be cached before requesting fresh informa‐
tion 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 direc‐
tory should be cached before requesting fresh informa‐
tion from a server. The default is 30 seconds.
acdirmax=n The maximum time in seconds that attributes of a direc‐
tory can be cached before requesting fresh information
from a server. The default is 60 seconds.
actimeo=n Using actimeo sets all of acregmin, acregmax, 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 for forground mounts is 2 minutes. The
default value for background mounts 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 charac‐
ters.
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 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.
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.
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.
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.
vers=n vers is an alternative to nfsvers and is compatible with
many other operating systems.
nolock Disable NFS locking. Do not start lockd. This has to be
used with some old NFS servers that don't support lock‐
ing.
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.
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 timeout then report
an I/O error to the calling program. The default is to
continue retrying NFS file operations indefinitely.
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.
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.
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.
nocto Suppress the retrieval of new attributes when creating a
file.
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.
noacl Disables Access Control List (ACL) processing.
sec=mode Set the security flavor for this mount to "mode". The
default setting is sec=sys, which uses local unix uids
and gids to authenticate NFS operations (AUTH_SYS).
Other currently supported settings are: sec=krb5, which
uses Kerberos V5 instead of local unix uids and gids to
authenticate users; sec=krb5i, which uses Kerberos V5
for user authentication and performs integrity checking
of NFS operations using secure checksums to prevent data
tampering; and sec=krb5p, 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.
tcp Mount the NFS filesystem using the TCP protocol instead
of the default UDP protocol. Many NFS servers only sup‐
port UDP.
udp Mount the NFS filesystem using the UDP protocol. This
is the default.
fsc Enable the use of persistent caching to the local disk
using the FS-Cache facility for the given mount point.
All of the non-value options have corresponding nooption forms. For
example, nointr means don't allow file operations to be interrupted.
Options for the nfs4 file system type
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.
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 max‐
imum 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.
timeo=n The value in tenths of a second before sending the first
retransmission after an RPC timeout. The default value
depends on whether proto=udp or 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.
retrans=n The number of minor timeouts and retransmissions that
must occur before a major timeout occurs. The default
is 5 timeouts for proto=udp and 2 timeouts for
proto=tcp. When a major timeout occurs, the file opera‐
tion is either aborted or a "server not responding" mes‐
sage is printed on the console.
acregmin=n The minimum time in seconds that attributes of a regular
file should be cached before requesting fresh informa‐
tion 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 direc‐
tory should be cached before requesting fresh informa‐
tion from a server. The default is 30 seconds.
acdirmax=n The maximum time in seconds that attributes of a direc‐
tory can be cached before requesting fresh information
from a server. The default is 60 seconds.
actimeo=n Using actimeo sets all of acregmin, acregmax, 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 for forground mounts is 2 minutes. The
default value for background mounts is 10000 minutes,
which is roughly one week.
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.
proto=n Mount the NFS filesystem using a specific network proto‐
col instead of the default UDP protocol. Many NFS ver‐
sion 4 servers only support TCP. Valid protocol types
are udp and tcp.
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.
sec=mode Same as sec=mode for the nfs filesystem type (see
above).
bg If an NFS mount attempt times out, retry the mount in
the background. After a mount operation is back‐
grounded, all subsequent mounts on the same NFS server
will be backgrounded immediately, without first attempt‐
ing 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 timeout then report
an I/O error to the calling program. The default is to
continue retrying NFS file operations indefinitely.
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.
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.
nocto Suppress the retrieval of new attributes when creating a
file.
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.
fsc Enable the use of persistent caching to the local disk
using the FS-Cache facility for the given mount point.
All of the non-value options have corresponding nooption forms. For
example, nointr means don't allow file operations to be interrupted.
FILES
/etc/fstab
SEE ALSOfstab(5), mount(8), umount(8), exports(5)AUTHOR
"Rick Sladkey" <jrs@world.std.com>
BUGS
The posix, and nocto options are parsed by mount but currently are
silently ignored.
The tcp and namlen options are implemented but are not currently sup‐
ported by the Linux kernel.
The umount command should notify the server when an NFS filesystem is
unmounted.
Checking files on NFS filesystem referenced by file descriptors (i.e.
the fcntl and ioctl families of functions) may lead to inconsistent
result due to the lack of consistency check in kernel even if noac is
used.
Linux 0.99 20 November 1993 NFS(5)
