path: root/sbin/mount/mount.8

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.\"     @(#)mount.8	8.7 (Berkeley) 3/27/94
.\"
.Dd March 27, 1994
.Dt MOUNT 8
.Os
.Sh NAME
.Nm mount
.Nd mount file systems
.Sh SYNOPSIS
.Nm mount
.Op Fl Aadfruvw
.Op Fl t Ar type
.Nm mount
.Op Fl dfruvw
.Ar special | node
.Nm mount
.Op Fl dfruvw
.Op Fl o Ar options
.Op Fl t Ar type
.Ar special node
.Sh DESCRIPTION
The
.Nm
command invokes a file system specific program to prepare
and graft the
.Ar special
device or 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
For disk partitions, the
.Ar special
device must correspond to a partition registered in the
.Xr disklabel 5 .
.Pp
The system maintains a list of currently mounted file systems.
If no arguments are given to
.Nm mount ,
this list is printed.
.Pp
A mount point
.Ar node
must be an existing directory for a mount to succeed
.Po
except in the special case of
.Pa / ,
of course
.Pc .
Only the superuser may mount file systems unless
.Va kern.usermount
is nonzero
.Po
see
.Xr sysctl 8
.Pc ,
the
.Ar special
device
is readable and writeable by the user attempting the mount,
and the mount point
.Ar node
is owned by the user attempting the mount.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl A
Causes
.Nm
to try to mount all of the file systems listed in the
.Xr fstab 5
table except those for which the
.Dq noauto
option is specified.
.It Fl a
Similar to the
.Fl A
flag, except that if a file system (other than the root file system)
appears to be already mounted,
.Nm
will not try to mount it again.
.Nm
assumes that a file system is already mounted if a file system with
the same type is mounted on the given mount point.
More stringent checks are not possible because some file system types
report strange values for the mounted-from device for mounted file
systems.
.It Fl d
Causes everything to be done except for the invocation of
the file system specific program.
This option is useful in conjunction with the
.Fl v
flag to
determine what the
.Nm
command is trying to do.
.It Fl f
Either force mounting of dirty file systems or, in the case of a
downgrade from read-write to read-only operation, the revocation of
opened files with write access.
.It Fl o Ar options
Options can be given with (or without) a
.Sq no
prefix to invert their meaning.
The options listed below specify non-default values.
For example,
.Sq noasync
is the default, so
.Sq async
can be used to mount a file system asynchronously.
Multiple options can be specified in a comma-separated list.
The available options are as follows:
.Bl -tag -width Ds
.It async
All
.Tn I/O
to the file system should be done asynchronously.
This is a
.Em dangerous
flag to set since it does not guarantee to keep a consistent
file system structure on the disk.
You should not use this flag
unless you are prepared to recreate the file system should your
system crash.
The most common use of this flag is to speed up
.Xr restore 8
where it can give a factor of two speed increase.
.It softdep
(FFS only.)
Mount the file system using soft dependencies.
Instead of metadata being written immediately, it is written in an ordered
fashion to keep the on-disk state of the file system consistent.
This results in significant speedups for file create/delete operations.
This option will be ignored when using the
.Fl u
flag and a file system is already mounted read/write.
It requires
.Cm option FFS_SOFTUPDATES
to be enabled in the running kernel.
.It force
The same as
.Fl f ;
forces the revocation of write access when trying to downgrade
a file system mount status from read-write to read-only.
.It noatime
Do not update atime on files in the system unless the mtime or ctime
is being changed as well.
This option is useful for laptops and news servers where one does
not want the extra disk activity associated with updating the atime.
.It noaccesstime
Synonym for noatime provided for compatibility with
other operating systems.
.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 superuser 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 file system root and the existing directory.
Lookups will be done in the mounted file system first.
If those operations fail due to a non-existent file the underlying
directory is then accessed.
All creates are done in the mounted file system.
.El
.Pp
Any additional options specific to a given file system type (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
.Nm
command:
.Bd -literal -offset indent
# mount -t mfs -o nosuid,-s=4000 /dev/sd0b /tmp
.Ed
.Pp
causes
.Nm
to execute the equivalent of:
.Bd -literal -offset indent
# /sbin/mount_mfs -o nosuid -s 4000 /dev/sd0b /tmp
.Ed
.It Fl r
The file system is to be mounted read-only.
Mount the file system read-only (even the superuser may not write it).
The same as the
.Dq rdonly
argument to the
.Fl o
option.
.It Fl t Ar type
The argument following the
.Fl t
is used to indicate the file system type.
The type
.Ar ffs
is the default.
The
.Fl t
option can be used
to indicate that the actions should only be taken on
file systems of the specified type.
More than one type may be specified in a comma separated list.
The list of file system types can be prefixed with
.Dq no
to specify the file system types for which action should
.Em not
be taken.
For example, the
.Nm
command:
.Bd -literal -offset indent
# mount -a -t nonfs,mfs
.Ed
.Pp
mounts all file systems except those of type
.Tn NFS
and
.Tn MFS .
.Pp
.Nm
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 file systems are mounted by the program
.Pa /sbin/mount_nfs .
.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 file system are currently open for writing unless the
.Fl f
flag is also specified.
Only options specified on the command line with
.Fl o
are changed;
other file system options are unaltered.
The options set in the
.Xr fstab 5
table are ignored.
.It Fl v
Verbose mode.
.It Fl w
The file system object is to be read and write.
.El
.Pp
The options specific to the various file system types are
described in the manual pages for those file systems'
.Nm mount_XXX
commands.
For instance, the options specific to Berkeley
Fast File Systems are described in the
.Xr mount_ffs 8
manual page.
.Sh FILES
.Bl -tag -width /etc/fstab -compact
.It Pa /etc/fstab
file system table
.El
.Sh EXAMPLES
Mount a CD-ROM on node
.Pa /mnt/cdrom :
.Pp
.Dl # mount -t cd9660 -r /dev/cd0a /mnt/cdrom
.Pp
Mount an MS-DOS floppy on node
.Pa /mnt/floppy :
.Pp
.Dl # mount -t msdos /dev/fd0a /mnt/floppy
.Pp
Graft a remote NFS file system on host
.Ar host ,
path
.Pa /path/name ,
on node
.Pa /mnt/nfs :
.Pp
.Dl # mount host:/path/name /mnt/nfs
.Pp
Remount
.Pa /var
with option
.Dq dev :
.Pp
.Dl # mount -u -o dev /var
.Sh SEE ALSO
.Xr mount 2 ,
.Xr fstab 5 ,
.Xr disklabel 8 ,
.Xr mount_ados 8 ,
.Xr mount_cd9660 8 ,
.Xr mount_ext2fs 8 ,
.Xr mount_fdesc 8 ,
.Xr mount_ffs 8 ,
.Xr mount_kernfs 8 ,
.Xr mount_mfs 8 ,
.Xr mount_msdos 8 ,
.Xr mount_nfs 8 ,
.Xr mount_ntfs 8 ,
.Xr mount_null 8 ,
.Xr mount_portal 8 ,
.Xr mount_procfs 8 ,
.Xr mount_umap 8 ,
.Xr mount_union 8 ,
.Xr mount_xfs 8 ,
.Xr sysctl 8 ,
.Xr umount 8
.Sh HISTORY
A
.Nm
command appeared in
.At v3 .
.Sh CAVEATS
After a successful
.Nm mount ,
the permissions on the original mount point determine if
.Dq \&.\&.
is accessible from the mounted file system.
The minimum permissions for
the mount point for traversal across the mount point in both
directions to be possible for all users is 0111 (execute for all).