freebsd-dev/sbin/mount/mount.8

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.\"     @(#)mount.8	8.8 (Berkeley) 6/16/94
.\" $FreeBSD$
.\"
.Dd June 16, 1994
.Dt MOUNT 8
.Os
.Sh NAME
.Nm mount
.Nd mount filesystems
.Sh SYNOPSIS
.Nm
.Op Fl adfpruvw
.Op Fl t Ar ufs | external_type
.Nm
.Op Fl dfpruvw
.Ar special | node
.Nm
.Op Fl dfpruvw
.Op Fl o Ar options
.Op Fl t Ar ufs | external_type
.Ar special node
.Sh DESCRIPTION
The
.Nm
utility calls the
.Xr mount 2
system call to prepare and graft a
.Ar "special device"
or the remote node (rhost:path) on to the filesystem 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 filesystems.
If no arguments are given to
.Nm ,
this list is printed.
.Pp
The options are as follows:
.Bl -tag -width indent
.It Fl a
All the filesystems described in
.Xr fstab 5
are mounted.
Exceptions are those marked as
.Dq noauto ,
excluded by the
.Fl t
flag (see below), or if they are already mounted (except the
root filesystem which is always remounted to preserve
traditional single user mode behavior).
.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
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.
In case of conflicting options being specified, the rightmost option
takes effect.
The following options are available:
.Bl -tag -width indent
.It Cm async
All
.Tn I/O
to the filesystem 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 Cm current
When used with the
.Fl u
flag, this is the same as specifying the options currently in effect for
the mounted filesystem.
.It Cm 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 Cm fstab
When used with the
.Fl u
flag, this is the same as specifying all the options listed in the
.Xr fstab 5
file for the filesystem.
.It Cm noasync
Metadata I/O should be done synchronously, while data I/O should be done
asynchronously.
This is the default.
.It Cm noatime
Do not update the file access time when reading from a file.
This option
is useful on filesystems where there are large numbers of files and
performance is more critical than updating the file access time (which is
rarely ever important).
This option is currently only supported on local filesystems.
.It Cm noauto
This filesystem should be skipped when
.Nm
is run with the
.Fl a
flag.
.It Cm noclusterr
Disable read clustering.
.It Cm noclusterw
Disable write clustering.
.It Cm nodev
Do not interpret character or block special devices on the filesystem.
This option is useful for a server that has filesystems containing
special devices for architectures other than its own.
.It Cm noexec
Do not allow execution of any binaries on the mounted filesystem.
This option is useful for a server that has filesystems containing
binaries for architectures other than its own.
.It Cm nosuid
Do not allow set-user-identifier or set-group-identifier bits to take effect.
Note: this option is worthless if a public available suid or sgid
wrapper like
.Xr suidperl 1
is installed on your system.
.It Cm nosymfollow
Do not follow symlinks
on the mounted filesystem.
.It Cm rdonly
The same as
.Fl r ;
mount the filesystem read-only (even the super-user may not write it).
.It Cm sync
All
.Tn I/O
to the filesystem should be done synchronously.
.It Cm snapshot
This option allows a snapshot of the specified filesystem to be taken.
The
.Fl u
flag is required with this option.
Note that snapshot files must be created in the filesystem that is being
snapshotted.
You may create up to 20 snapshots per filesystem.
Active snapshots are recorded in the superblock, so they persist across unmount
and remount operations and across system reboots.
When you are done with a snapshot, it can be removed with the
.Xr rm
command.
Snapshots may be removed in any order, however you may not get back all the
space contained in the snapshot as another snapshot may claim some of the blocks
that it is releasing.
Note that the schg flag is set on snapshots to ensure that not even the root
user can write to them.
The unlink command makes an exception for snapshot files in that it allows them
to be removed even though they have the schg flag set, so it is not necessary to
clear the schg flag before removing a snapshot file.
.Pp
Once you have taken a snapshot, there are three interesting things that you can 
do with it:
.Pp
.Bl -enum -compact
.It
Run fsck on the snapshot file.
Assuming that the filesystem was clean when it was mounted, you should always
get a clean (and unchanging) result from running fsck on the snapshot.
This is essentially what the background fsck process does.
.Pp
.It
Run dump on the snapshot.
You will get a dump that is consistent with the filesystem as of the timestamp
of the snapshot.
Note that
.Xr dump
has not yet been changed to set the dumpdates file correctly, so do not use this
feature in production until that fix is made.
.Pp
.It
Mount the snapshot as a frozen image of the filesystem.
To mount the snapshot
.Pa /var/snapshot/snap1 :
.Bd -literal
mdconfig -a -t vnode -f /var/snapshot/snap1 -u 4
mount -r /dev/md4 /mnt
.Ed
.Pp
You can now cruise around your frozen
.Pa /var
filesystem at
.Pa /mnt .
Everything will be in the same state that it was at the time the snapshot was
taken.
The one exception is that any earlier snapshots will appear as zero length
files.
When you are done with the mounted snapshot:
.Bd -literal
umount /mnt
mdconfig -d -u 4
.Ed
.Pp
Further details can be found in the file at
.Pa /usr/src/sys/ufs/ffs/README.snapshot .
.El
.It Cm suiddir
A directory on the mounted filesystem will respond to the SUID bit
being set, by setting the owner of any new files to be the same
as the owner of the directory.
New directories will inherit the bit from their parents.
Execute bits are removed from
the file, and it will not be given to root.
.Pp
This feature is designed for use on fileservers serving PC users via
ftp, SAMBA, or netatalk.
It provides security holes for shell users and as
such should not be used on shell machines, especially on home directories.
This option requires the SUIDDIR
option in the kernel to work.
Only UFS filesystems support this option.
See
.Xr chmod 2
for more information.
.It Cm update
The same as
.Fl u ;
indicate that the status of an already mounted filesystem should be changed.
.It Cm 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
.Nm
command:
.Bd -literal -offset indent
mount -t unionfs -o -b /sys $HOME/sys
.Ed
.Pp
causes
.Nm
to execute the equivalent of:
.Bd -literal -offset indent
/sbin/mount_unionfs -b /sys $HOME/sys
.Ed
.Pp
Additional options specific to filesystem types
which are not internally known
(see the description of the
.Fl t
option below)
may be described in the manual pages for the associated
.Pa /sbin/mount_ Ns Sy XXX
utilities.
.It Fl p
Print mount information in
.Xr fstab 5
format.
Implies also the
.Fl v
option.
.It Fl r
The filesystem is to be mounted read-only.
Mount the filesystem read-only (even the super-user may not write it).
The same as the
.Cm rdonly
argument to the
.Fl o
option.
.It Fl t Ar ufs | external_type
The argument following the
.Fl t
is used to indicate the filesystem 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
command:
.Bd -literal -offset indent
mount -a -t nonfs,nullfs
.Ed
.Pp
mounts all filesystems except those of type
.Tn NFS
and
.Tn NULLFS .
.Pp
If the type is not one of the internally known types,
.Nm
will attempt to execute a program in
.Pa /sbin/mount_ Ns Sy XXX
where
.Sy 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
.Nm
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 filesystem 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 applying the options specified
in the argument to
.Fl o
and finally applying the
.Fl r
or
.Fl w
option.
.It Fl v
Verbose mode.
.It Fl w
The filesystem object is to be read and write.
.El
.Sh DIAGNOSTICS
Various, most of them are self-explanatory.
.Pp
.Dl XXXXX filesystem is not available
.Pp
The kernel does not support the respective filesystem type.
Note that
support for a particular filesystem might be provided either on a static
(kernel compile-time), or dynamic basis (loaded as a kernel module by
.Xr kldload 8 ) .
Normally,
.Nm
or its subprocesses attempt to dynamically load a filesystem module if
it has not been configured statically, using
.Xr vfsload 3 .
In this case, the above error message can also mean that you did not
have permission to load the module.
.Sh FILES
.Bl -tag -width /etc/fstab -compact
.It Pa /etc/fstab
filesystem table
.El
.Sh SEE ALSO
.Xr mount 2 ,
.Xr vfsload 3 ,
.Xr fstab 5 ,
.Xr kldload 8 ,
.Xr mount_cd9660 8 ,
.Xr mount_devfs 8 ,
.Xr mount_ext2fs 8 ,
.Xr mount_fdescfs 8 ,
.Xr mount_hpfs 8 ,
.Xr mount_linprocfs 8 ,
.Xr mount_msdosfs 8 ,
.Xr mount_nfs 8 ,
.Xr mount_ntfs 8 ,
.Xr mount_nullfs 8 ,
.Xr mount_nwfs 8 ,
.Xr mount_portalfs 8 ,
.Xr mount_procfs 8 ,
.Xr mount_smbfs 8 ,
.Xr mount_std 8 ,
.Xr mount_udf 8 ,
.Xr mount_umapfs 8 ,
.Xr mount_unionfs 8 ,
.Xr umount 8
.Sh BUGS
It is possible for a corrupted filesystem to cause a crash.
.Sh CAVEATS
After a successful
.Nm ,
the permissions on the original mount point determine if
.Pa ..\&
is accessible from the mounted filesystem.
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).
.Sh HISTORY
A
.Nm
utility appeared in
.At v1 .