nfs
NFS(5) Linux Programmer’s Manual NFS(5)
NAME
nfs - 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 time-
out, the timeout is doubled after each successive time-
out 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 net-
work, 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 respond-
ing" message is printed on the console.
acregmin=n The minimum time in seconds that attributes of a regu-
lar 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 regu-
lar file can be cached before requesting fresh informa-
tion 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.
nolock Disable NFS locking. Do not start lockd. This has to
be used with some old NFS servers that don’t support
locking.
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 con-
tinue 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 proto-
col. 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. Note that there is a performance
penalty when using integrity or privacy.
tcp Mount the NFS filesystem using the TCP protocol. This
is the default.
udp Mount the NFS filesystem using the UDP protocol instead
of the default TCP protocol.
nordirplus Disables NFSv3 READDIRPLUS RPCs. Use this option when
mounting servers that don’t support or have broken
READDIRPLUS implementations.
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
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 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 dou-
bled after each successive timeout until a maximum
timeout of 60 seconds is reached or the enough retrans-
missions 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 pre-
vious 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 oper-
ation 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 regu-
lar 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 regu-
lar file can be cached before requesting fresh informa-
tion 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 pro-
tocol instead of the default UDP protocol. Many NFS
version 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
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 con-
tinue 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.
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 ALSO
fstab(5), mount(8), umount(8), exports(5)
AUTHOR
"Rick Sladkey" <jrs@world.std.com>
BUGS
The posix option is implemented but is currently ignored by the Linux
kernel.
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)
