path: root/sbin/mount/mount.8

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.Dd $Mdocdate: October 6 2016 $
.Dt MOUNT 8
.Os
.Sh NAME
.Nm mount
.Nd mount file systems
.Sh SYNOPSIS
.Nm mount
.Op Fl AadfNruvw
.Op Fl t Ar type
.Nm mount
.Op Fl dfrsuvw
.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 is either a
.Xr disklabel 8
UID (DUID) or an entry in
.Pa /dev .
If it is a DUID,
it will be automatically mapped to the appropriate entry in
.Pa /dev .
In either case the partition must be present
in the disklabel loaded from the device.
The partition name is the last letter in the entry name.
For example, /dev/sd0a and 3eb7f9da875cb9ee.a both refer to the
.Sq a
partition.
.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.
.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 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
or
.Dq net
options are 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 N
If used with either
.Fl A
or
.Fl a ,
.Nm
will only look at file systems which have the
.Dq net
option specified.
By default file systems with the
.Dq net
option are ignored.
.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 nosoftdep
is the default, so
.Sq softdep
can be used to mount the file system using soft dependencies.
Multiple options can be specified in a comma-separated list.
The available options are as follows:
.Bl -tag -width 9n
.It async
Metadata I/O to the file system should be done asynchronously.
By default, only regular data is read/written asynchronously.
.Pp
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.
.Pp
The options
.Ic async
and
.Ic softdep
are mutually exclusive.
.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 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 noperm
(FFS only)
Do not check permissions when creating, accessing or modifying files and
directories in the mounted file system.
This allows unprivileged users to construct a file hierarchy containing
special device nodes and files with arbitrary file mode, owner or group
without restriction.
Only the owner, group and mode of the root directory of the filesystem
will be honored so access to the filesystem can be locked down.
The noperm option also enables the nodev and noexec options to ensure
that interpretation of the file modes and special devices cannot be
used to gain privileges.
.It norw
An alias for rdonly.
.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 ro
An alias for rdonly.
.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 is ignored when using the
.Fl u
flag and a file system is already mounted read/write.
.Pp
The options
.Ic async
and
.Ic softdep
are mutually exclusive.
.It sync
Regular data I/O to the file system should be done synchronously.
By default, only metadata is read/written synchronously.
.It update
The same as
.Fl u ;
indicate that the status of an already mounted file system should be changed.
.It wxallowed
Processes that ask for memory to be made writeable plus executable
using the
.Xr mmap 2
and
.Xr mprotect 2
system calls are killed by default.
This option allows those processes to continue operation.
It is typically used on the
.Pa /usr/local
filesystem.
.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:
.Bd -literal -offset 3n
# mount -t mfs -o rw,nodev,nosuid,-s=153600 /dev/sd0b /tmp
.Ed
.Pp
That causes
.Nm
to execute the equivalent of:
.Bd -literal -offset 3n
# /sbin/mount_mfs -o rw,nodev,nosuid -s 153600 /dev/sd0b /tmp
.Ed
.Pp
The equivalent example in
.Xr fstab 5
would be:
.Bd -literal -offset 3n
swap /tmp mfs rw,nodev,nosuid,-s=153600 0 0
.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 s
Skip mounting the file system if it is already mounted.
See the
.Fl a
flag for a description of the criteria used to decide if a file system
is already mounted.
.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 NFS and 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 USB stick with DUID 3eb7f9da875cb9ee on node
.Pa /mnt/key :
.Pp
.Dl # mount -t msdos 3eb7f9da875cb9ee.i /mnt/key
.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_cd9660 8 ,
.Xr mount_ext2fs 8 ,
.Xr mount_ffs 8 ,
.Xr mount_mfs 8 ,
.Xr mount_msdos 8 ,
.Xr mount_nfs 8 ,
.Xr mount_ntfs 8 ,
.Xr mount_tmpfs 8 ,
.Xr mount_udf 8 ,
.Xr mount_vnd 8 ,
.Xr sysctl 8 ,
.Xr umount 8
.Sh HISTORY
A
.Nm
command appeared in
.At v1 .
.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).