NAME¶
mount_nfs —
mount NFS file
systems
SYNOPSIS¶
mount_nfs |
[-23bcdiLlNPsTU]
[-a
maxreadahead]
[-D
deadthresh]
[-g
maxgroups]
[-I
readdirsize]
[-o
options]
[-R
retrycnt]
[-r
readsize]
[-t
timeout]
[-w
writesize]
[-x
retrans]
rhost:path node |
DESCRIPTION¶
The
mount_nfs utility calls the
nmount(2)
system call to prepare and graft a remote NFS file system
(
rhost:
path) on to the file system
tree at the point
node. This command is normally
executed by
mount(8). It implements the mount protocol as
described in RFC 1094, Appendix A and
NFS: Network File
System Version 3 Protocol Specification, Appendix I.
If the file system type is specified as ``oldnfs'', which implies this command
is run as ``mount_oldnfs'', then it forces use of the old NFS client, which
does not support the
nfsv4 option.
By default,
mount_nfs keeps retrying until the mount succeeds.
This behaviour is intended for file systems listed in
fstab(5) that are critical to the boot process. For
non-critical file systems, the
bg and
retrycnt options provide mechanisms to prevent the boot
process from hanging if the server is unavailable.
If the server becomes unresponsive while an NFS file system is mounted, any new
or outstanding file operations on that file system will hang uninterruptibly
until the server comes back. To modify this default behaviour, see the
intr and
soft options.
The options are:
- -o
- Options are specified with a -o flag
followed by a comma separated string of options. See the
mount(8) man page for possible options and their
meanings. The following NFS specific options are also available:
- acregmin=⟨seconds⟩
-
- acregmax=⟨seconds⟩
-
- acdirmin=⟨seconds⟩
-
- acdirmax=⟨seconds⟩
- When attributes of files are cached, a timeout
calculated to determine whether a given cache entry has expired. These
four values determine the upper and lower bounds of the timeouts for
“directory” attributes and “regular” (ie:
everything else). The default values are 3 -> 60 seconds for
regular files, and 30 -> 60 seconds for directories. The algorithm
to calculate the timeout is based on the age of the file. The older
the file, the longer the cache is considered valid, subject to the
limits above.
- bg
- If an initial attempt to contact the server fails, fork
off a child to keep trying the mount in the background. Useful for
fstab(5), where the file system mount is not
critical to multiuser operation.
- deadthresh=⟨value⟩
- Set the “dead server threshold” to the
specified number of round trip timeout intervals before a
“server not responding” message is displayed.
- dumbtimer
- Turn off the dynamic retransmit timeout estimator. This
may be useful for UDP mounts that exhibit high retry rates, since it
is possible that the dynamically estimated timeout interval is too
short.
- fg
- Same as not specifying bg.
- hard
- Same as not specifying soft.
- intr
- Make the mount interruptible, which implies that file
system calls that are delayed due to an unresponsive server will fail
with EINTR when a termination signal is posted for the process.
- maxgroups=⟨value⟩
- Set the maximum size of the group list for the
credentials to the specified value. This should be used for mounts on
old servers that cannot handle a group list size of 16, as specified
in RFC 1057. Try 8, if users in a lot of groups cannot get response
from the mount point.
- mntudp
- Force the mount protocol to use UDP transport, even for
TCP NFS mounts. (Necessary for some old BSD
servers.)
- negnametimeo=⟨value⟩
- Override the default of NFS_DEFAULT_NEGNAMETIMEO for
the timeout (in seconds) for negative name cache entries. If this is
set to 0 it disables negative name caching for the mount point.
- nfsv2
- Use the NFS Version 2 protocol (the default is to try
version 3 first then version 2). Note that NFS version 2 has a file
size limit of 2 gigabytes.
- nfsv3
- Use the NFS Version 3 protocol.
- nfsv4
- Use the NFS Version 4 protocol. This option will force
the mount to use TCP transport.
- noconn
- For UDP mount points, do not do a
connect(2). This must be used if the server does not
reply to requests from the standard NFS port number 2049 or replies to
requests using a different IP address (which can occur if the server
is multi-homed). Setting the
vfs.nfs.nfs_ip_paranoia sysctl to 0 will make
this option the default.
- nocto
- Normally, NFS clients maintain the close-to-open cache
coherency. This works by flushing at close time and checking at open
time. Checking at open time is implemented by getting attributes from
the server and purging the data cache if they do not match attributes
cached by the client.
This option disables checking at open time. It may improve performance
for read-only mounts, but should only be used if the data on the
server changes rarely. Be sure to understand the consequences before
enabling this option.
- noinet4,
noinet6
- Disables
AF_INET
or
AF_INET6
connections. Useful for hosts that
have both an A record and an AAAA record for the same name.
- nolockd
- Do not forward
fcntl(2) locks over the wire. All locks will be
local and not seen by the server and likewise not seen by other NFS
clients. This removes the need to run the rpcbind(8)
service and the rpc.statd(8) and
rpc.lockd(8) servers on the client. Note that this
option will only be honored when performing the initial mount, it will
be silently ignored if used while updating the mount options.
- principal
- For the RPCSEC_GSS security flavors, such as krb5,
krb5i and krb5p, this option sets the name of the host based principal
name expected by the server. This option overrides the default, which
will be ``nfs@<server-fqdn>'' and should normally be
sufficient.
- noresvport
- Do not use a reserved socket port
number (see below).
- port=⟨port_number⟩
- Use specified port number for NFS requests. The default
is to query the portmapper for the NFS port.
- rdirplus
- Used with NFSV3 to specify that the ReaddirPlus
RPC should be used. For NFSV4, setting this option has a similar
effect, in that it will make the Readdir Operation get more
attributes. This option reduces RPC traffic for cases such as
“ls -l”, but tends to flood the attribute and name caches
with prefetched entries. Try this option and see whether performance
improves or degrades. Probably most useful for client to server
network interconnects with a large bandwidth times delay product.
- readahead=⟨value⟩
- Set the read-ahead count to the specified value. This
may be in the range of 0 - 4, and determines how many blocks will be
read ahead when a large file is being read sequentially. Trying a
value greater than 1 for this is suggested for mounts with a large
bandwidth * delay product.
- readdirsize=⟨value⟩
- Set the readdir read size to the specified value. The
value should normally be a multiple of
DIRBLKSIZ
that is <= the read size for the
mount.
- resvport
- Use a reserved socket port number. This flag is
obsolete, and only retained for compatibility reasons. Reserved port
numbers are used by default now. (For the rare case where the client
has a trusted root account but untrustworthy users and the network
cables are in secure areas this does help, but for normal desktop
clients this does not apply.)
- retrans=⟨value⟩
- Set the retransmit timeout count for soft mounts to the
specified value.
- retrycnt=⟨count⟩
- Set the mount retry count to the specified value. The
default is a retry count of zero, which means to keep retrying
forever. There is a 60 second delay between each attempt.
- rsize=⟨value⟩
- Set the read data size to the specified value. It
should normally be a power of 2 greater than or equal to 1024. This
should be used for UDP mounts when the “fragments dropped due to
timeout” value is getting large while actively using a mount
point. (Use netstat(1) with the -s
option to see what the “fragments dropped due to timeout”
value is.)
- sec=⟨flavor⟩
- This option specifies what security flavor should be
used for the mount. Currently, they are:
krb5 - Use KerberosV authentication
krb5i - Use KerberosV authentication and
apply integrity checksums to RPCs
krb5p - Use KerberosV authentication and
encrypt the RPC data
sys - The default AUTH_SYS, which uses a
uid + gid list authenticator
- soft
- A soft mount, which implies that file system calls will
fail after retrycnt round trip timeout
intervals.
- tcp
- Use TCP transport. This is the default option, as it
provides for increased reliability on both LAN and WAN configurations
compared to UDP. Some old NFS servers do not support this method; UDP
mounts may be required for interoperability.
- timeout=⟨value⟩
- Set the initial retransmit timeout to the specified
value. May be useful for fine tuning UDP mounts over internetworks
with high packet loss rates or an overloaded server. Try increasing
the interval if nfsstat(1) shows high retransmit
rates while the file system is active or reducing the value if there
is a low retransmit rate but long response delay observed. (Normally,
the dumbtimer option should be specified when using
this option to manually tune the timeout interval.)
- udp
- Use UDP transport.
- wsize=⟨value⟩
- Set the write data size to the specified value. Ditto
the comments w.r.t. the rsize option, but using the
“fragments dropped due to timeout” value on the server
instead of the client. Note that both the rsize and
wsize options should only be used as a last ditch
effort at improving performance when mounting servers that do not
support TCP mounts.
COMPATIBILITY¶
The following command line flags are equivalent to
-o named
options and are supported for compatibility with older installations.
- -2
- Same as -o nfsv2
- -3
- Same as -o nfsv3
- -D
- Same as -o
deadthresh
- -I
- Same as -o
readdirsize=⟨value⟩
- -L
- Same as -o nolockd
- -N
- Same as -o
noresvport
- -P
- Use a reserved socket port number. This flag is obsolete,
and only retained for compatibility reasons. (For the rare case where the
client has a trusted root account but untrustworthy users and the network
cables are in secure areas this does help, but for normal desktop clients
this does not apply.)
- -R
- Same as -o
retrycnt=⟨value⟩
- -T
- Same as -o tcp
- -U
- Same as -o mntudp
- -a
- Same as -o
readahead=⟨value⟩
- -b
- Same as -o bg
- -c
- Same as -o noconn
- -d
- Same as -o
dumbtimer
- -g
- Same as -o
maxgroups
- -i
- Same as -o intr
- -l
- Same as -o
rdirplus
- -r
- Same as -o
rsize=⟨value⟩
- -s
- Same as -o soft
- -t
- Same as -o
retransmit=⟨value⟩
- -w
- Same as -o
wsize=⟨value⟩
- -x
- Same as -o
retrans=⟨value⟩
SEE ALSO¶
nmount(2),
unmount(2),
nfsv4(4),
fstab(5),
gssd(8),
mount(8),
nfsd(8),
nfsiod(8),
showmount(8)
BUGS¶
Since nfsv4 performs open/lock operations that have their ordering strictly
enforced by the server, the options
intr and
soft cannot be safely used.
hard nfsv4
mounts are strongly recommended.