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.\"     @(#)mount.8	8.7 (Berkeley) 3/27/94
.\"
.Dd March 27, 1994
.Dt MOUNT 8
.Os BSD 4
.Sh NAME
.Nm mount
.Nd mount file systems
.Sh SYNOPSIS
.Nm mount
.Op Fl adfruvw
.Op Fl t Ar ufs | lfs | external_type
.Nm mount
.Op Fl dfruvw
.Ar special | node
.Nm mount
.Op Fl dfruvw
.Op Fl o Ar options
.Op Fl t Ar ufs | lfs | external_type
.Ar special node
.Sh DESCRIPTION
The
.Nm mount
command
calls the
.Xr mount 2
system call to prepare and graft a
.Ar "special device"
or the remote node (rhost:path) on to the file system tree at the point
.Ar node .
If either
.Ar special
or
.Ar node
are not provided, the appropriate information is taken from the
.Xr fstab 5
file.
.Pp
The system maintains a list of currently mounted file systems.
If no arguments are given to
.Nm mount,
this list is printed.
.Pp
The options are as follows:
.Bl -tag -width indent
.It Fl d
Causes everything to be done except for the actual system call.
This option is useful in conjunction with the
.Fl v
flag to
determine what the
.Nm mount
command is trying to do.
.It Fl f
Forces the revocation of write access when trying to downgrade
a filesystem mount status from read-write to read-only. Also
forces the R/W mount of an unclean filesystem (dangerous; use with
caution).
.It Fl o
Options are specified with a
.Fl o
flag followed by a comma separated string of options.
The following options are available:
.Bl -tag -width indent
.It async
All
.Tn I/O
to the file system should be done asynchronously.
This is a
.Em dangerous
flag to set,
and should not be used unless you are prepared to recreate the file
system should your system crash.
.It force
The same as
.Fl f ;
forces the revocation of write access when trying to downgrade
a filesystem mount status from read-write to read-only. Also
forces the R/W mount of an unclean filesystem (dangerous; use with caution).
.It nodev
Do not interpret character or block special devices on the file system.
This option is useful for a server that has file systems containing
special devices for architectures other than its own.
.It noexec
Do not allow execution of any binaries on the mounted file system.
This option is useful for a server that has file systems containing
binaries for architectures other than its own.
.It nosuid
Do not allow set-user-identifier or set-group-identifier bits to take effect.
.It rdonly
The same as
.Fl r ;
mount the file system read-only (even the super-user may not write it).
.It sync
All
.Tn I/O
to the file system should be done synchronously.
.It update
The same as
.Fl u ;
indicate that the status of an already mounted file system should be changed.
.It union
Causes the namespace at the mount point to appear as the union
of the mounted filesystem root and the existing directory.
Lookups will be done in the mounted filesystem first.
If those operations fail due to a non-existent file the underlying
directory is then accessed.
All creates are done in the mounted filesystem.
.El
.Pp
Any additional options specific to a filesystem type that is not
one of the internally known types (see the
.Fl t
option) may be passed as a comma separated list; these options are
distinguished by a leading
.Dq \&-
(dash).
Options that take a value are specified using the syntax -option=value.
For example, the mount command:
.Bd -literal -offset indent
mount -t mfs -o nosuid,-N,-s=4000 /dev/dk0b /tmp
.Ed
.Pp
causes
.Nm mount
to execute the equivalent of:
.Bd -literal -offset indent
/sbin/mount_mfs -o nosuid -N -s 4000 /dev/dk0b /tmp
.Ed
.It Fl r
The file system is to be mounted read-only.
Mount the file system read-only (even the super-user may not write it).
The same as the
.Dq rdonly
argument to the
.Fl o
option.
.It Fl t Ar "ufs \\*(Ba lfs \\*(Ba external type"
The argument following the
.Fl t
is used to indicate the file system type.
The type
.Ar ufs
is the default.
The 
.Fl t
option can be used
to indicate that the actions should only be taken on
filesystems of the specified type.
More than one type may be specified in a comma separated list.
The list of filesystem types can be prefixed with
.Dq no
to specify the filesystem types for which action should
.Em not
be taken.
For example, the
.Nm mount
command:
.Bd -literal -offset indent
mount -a -t nonfs,mfs
.Ed
.Pp
mounts all filesystems except those of type
.Tn NFS
and
.Tn MFS .
.Pp
If the type is not one of the internally known types,
mount will attempt to execute a program in
.Pa /sbin/mount_ Ns Em XXX
where
.Em XXX
is replaced by the type name.
For example, nfs filesystems are mounted by the program
.Pa /sbin/mount_nfs .
.Pp
Most filesystems will be dynamically loaded by their mount programs
if not already present in the kernel, using the
.Xr vfsload 3
subroutine.  Because this mechanism requires writable temporary space,
the filesystem type containing
.Pa /tmp
must be compiled into the kernel, and the filesystems containing
.Pa /tmp 
and
.Pa /usr/bin/ld 
must be listed in
.Pa /etc/fstab
before any filesystems which might be dynamically loaded.
.It Fl u
The
.Fl u
flag indicates that the status of an already mounted file
system should be changed.
Any of the options discussed above (the
.Fl o
option)
may be changed;
also a file system can be changed from read-only to read-write
or vice versa.
An attempt to change from read-write to read-only will fail if any
files on the filesystem are currently open for writing unless the
.Fl f
flag is also specified.
The set of options is determined by first extracting the options
for the file system from the
.Xr fstab
table,
then applying any options specified by the
.Fl o
argument,
and finally applying the
.Fl r
or
.Fl w
option.
.It Fl v
Verbose mode.
.It Fl w
The file system object is to be read and write.
.Pp
The options specific to NFS filesystems are described in the
.Xr mount_nfs 8
manual page.
.Sh FILES
.Bl -tag -width /etc/fstab -compact
.It Pa /etc/fstab
file system table
.El
.Sh SEE ALSO
.Xr mount 2 ,
.Xr vfsload 3 ,
.Xr fstab 5 ,
.Xr mount_cd9660 8 ,
.Xr mount_fdesc 8 ,
.Xr mount_kernfs 8 ,
.Xr mount_lfs 8 ,
.Xr mount_lofs 8 ,
.Xr mount_mfs 8 ,
.Xr mount_nfs 8 ,
.Xr mount_null 8 ,
.Xr mount_portal 8 ,
.Xr mount_procfs 8 ,
.Xr mount_umap 8 ,
.Xr mount_union 8 ,
.Xr umount 8
.Sh BUGS
It is possible for a corrupted file system to cause a crash.
.Sh HISTORY
A
.Nm mount
command appeared in
.At v6 .