mount_nfs(1M) Maintenance Commands mount_nfs(1M)
NAME
mount_nfs - mount remote NFS resources
SYNOPSIS
mount [ -F nfs ] [ -r ] [ -m ] [ -o specific_options ]
[ -O ] resource | mount_point
DESCRIPTION
mount attaches a named resource to the file system hierarchy
at the pathname location mount_point, which must already
exist. If mount_point has any contents prior to the mount
operation, the contents remain hidden until the resource is
once again unmounted.
If the resource is listed in the vfstab file, the command
line can specify either resource or mount_point, and mount
will consult vfstab for more information. If the -F option
is omitted, mount takes the file system type from vfstab.
mount maintains a table of mounted file systems in
/etc/mnttab, described in mnttab(4).
OPTIONS
-r Mount the specified file system read-only.
-m Do not append an entry to the /etc/mnttab table of
mounted file systems
-o specific_options
Set file system specific options according to a comma-
separated list chosen from words below.
rw|ro resource is mounted read-write or read-
only. The default is rw.
suid|nosuid Setuid execution allowed or disallowed.
The default is suid.
remount If a file system is mounted read-only,
remounts the file system read-write.
bg|fg If the first attempt fails, retry in the
background, or, in the foreground. The
default is fg.
retry=n The number of times to retry the mount
operation. The default is 10000.
port=n The server IP port number. The default
is NFS_PORT.
grpid By default, the GID associated with a
neewly created file will obey the System
V semantics; that is, the GID is set to
the effective GID of the calling pro-
cess. This behavior may be overridden
on a per-directory basis by setting the
set-GID bit of the parent directory; in
this case, the GID of a newly created
file is set to the GID of the parent
directory (see open(2) and mkdir(2)).
Files created on file systems that are
mounted with the grpid option will obey
BSD semantics independent of whether the
set-GID bit of the parent directory is
set; that is, the GID is unconditionally
inherited from that of the parent direc-
tory.
rsize=n Set the read buffer size to n bytes.
The default value is 8192.
wsize=n Set the write buffer size to n bytes.
The default value is 8192.
timeo=n Set the NFS timeout to n tenths of a
second. The default value is 11.
retrans=n Set the number of NFS retransmissions to
n. The default value is 5.
soft|hard Return an error if the server does not
respond, or continue the retry request
until the server responds. The default
value is hard.
intr|nointr Allow (do not allow) keyboard interrupts
to kill a process that is hung while
waiting for a response on a hard-mounted
file system. The default is intr.
secure Use DES authentication for NFS transac-
tions.
posix Request POSIX.1 semantics for the file
system. Requires a mount version 2
mountd(1M) on the server.
kerberos Use Kerberos authentication for NFS
transactions.
noac Suppress attribute caching.
acregmin=n Hold cached attributes for at least n
seconds after file modification. The
default value is 3.
acregmax=n Hold cached attributes for no more than
n seconds after file modification. The
default value is 60.
acdirmin=n Hold cached attributes for at least n
seconds after directory update. The
default value is 30.
acdirmax=n Hold cached attributes for no more than
n seconds after directory update. The
default value is 60.
actimeo=n Set min and max times for regular files
and directories to n seconds.
-O Overlay mount. Allow the file system to be mounted
over an existing mount point, making the underlying
file system inaccessible. If a mount is attempted on a
pre-existing mount point without setting this flag, the
mount will fail, producing the error "device busy".
NFS FILE SYSTEMS
Background vs. Foreground
File systems mounted with the bg option indicate that
mount is to retry in the background if the server's
mount daemon (mountd(1M)) does not respond. mount
retries the request up to the count specified in the
retry=n option. Once the file system is mounted, each
NFS request made in the kernel waits timeo=n tenths of
a second for a response. If no response arrives, the
time-out is multiplied by 2 and the request is
retransmitted. When the number of retransmissions has
reached the number specified in the retrans=n option, a
file system mounted with the soft option returns an
error on the request; one mounted with the hard option
prints a warning message and continues to retry the
request.
Hard vs. Soft
File systems that are mounted read-write or that con-
tain executable files should always be mounted with the
hard option. Applications using soft mounted filesys-
tems may incur unexpected I/O errors.
Authenticated Requests
The server may require authenticated NFS requests from
the client. Either secure or kerberos authentication
may be required.
File Attributes
To improve NFS read performance, files and file attributes
are cached. File modification times get updated whenever a
write occurs. However, file access times may be temporarily
out-of-date until the cache gets refreshed.
The attribute cache retains file attributes on the client.
Attributes for a file are assigned a time to be flushed. If
the file is modified before the flush time, then the flush
time is extended by the time since the last modification
(under the assumption that files that changed recently are
likely to change soon). There is a minimum and maximum
flush time extension for regular files and for directories.
Setting actimeo=n sets flush time to n seconds for both reg-
ular files and directories.
EXAMPLES
To mount an NFS file system:
example# mount serv:/usr/src /usr/src
To mount an NFS file system readonly with no suid
privileges:
example# mount -r -o nosuid serv:/usr/src /usr/src
FILES
/etc/mnttab table of mounted file systems
/etc/dfs/fstypes default distributed file system type
/etc/vfstab table of automatically mounted resources
SEE ALSO
mountall(1M), mountd(1M), mkdir(2), mount(2), open(2),
umount(2), mnttab(4)
NOTES
If the directory on which a file system is to be mounted is
a symbolic link, the file system is mounted on the directory
to which the symbolic link refers, rather than being mounted
on top of the symbolic link itself.
SunOS 4.X used the biod maintenance procedure to perform
parrallel read-ahead and write-behind on NFS clients. SunOS
5.X obsoleted biod with multi-threaded processing, which
transparently performs parallel read-ahead and write-behind.
SunOS 5.4 Last change: 3 Mar 1994