mount directories of partitions, not partitions possible?

kpachopoulos · 09-02-2007, 02:29 PM

Hi,
is it possible to mount a directory of a local hard disk, not the whole hard disk?
Something like:
/dev/hda1:/shared/xdir /somewhere/here auto defaults 0 0

stress_junkie · 09-02-2007, 02:32 PM

No. It is not possible to mount a subdirectory on a partition.

macemoneta · 09-02-2007, 02:34 PM

You don't mount disks, you mount filesystems. The unit of a filesystem is typically a partition, though there are other variants. Directories are structures within a filesystem, and as such don't meet the requirement.

pixellany · 09-02-2007, 02:36 PM

Normally, you mount devices to mount points. Devices = partitions, floppies, CD's, etc. It is not possible to mount a whole drive--only partitions.

Then there is the "bind" option to mount a directory to a mount point. See "man mount" for details.

pixellany · 09-02-2007, 02:39 PM

Quote:

Originally Posted by stress_junkie

No. It is not possible to mount a subdirectory on a partition.

That's OK, because that's not what he asked....

You can mount devices and directories---but only TO mountpoints (which are really directories.....confused yet??..

)

stress_junkie · 09-02-2007, 02:44 PM

Quote:

Originally Posted by pixellany

That's OK, because that's not what he asked....

You can mount devices and directories---but only TO mountpoints (which are really directories.....confused yet??..

)

I'm not really sure. I thought that the question was to mount a subdirectory on a partition into the mounted file system. I don't know.

I thought that mount --bind would create a second access point to a mounted partition, not mount a subdirectory on a partition.

Code:

mount /dev/hda3 /mnt/hda3
mount --bind /mnt/hda3 /home

I know for a fact that the above two commands work because I just tested them.

It seemed to me that the OP wanted to do something like this.

Code:

mount /dev/hda3/subdir /somewhere

... which AFAIK is not permitted.

pixellany · 09-02-2007, 04:19 PM

Deep breath.....

I **think** it works like this:

You can mount a device to a mountpoint. "device" means partition, floppy disk, etc. the device would have to have an entry in /dev.
Using bind, you can mount a directory to another directory (aka mountpoint). This assumes that the partition containing said directory is already mounted somewhere.
You cannot mount TO anything except a mountpoint (aka directory)
You cannot use bind to mount something prefixed with a /dev pathname--ie you can only mount directories to directories

stress_junkie · 09-02-2007, 06:48 PM

Quote:

Originally Posted by pixellany

Deep breath.....

I **think** it works like this:

You can mount a device to a mountpoint. "device" means partition, floppy disk, etc. the device would have to have an entry in /dev.
Using bind, you can mount a directory to another directory (aka mountpoint). This assumes that the partition containing said directory is already mounted somewhere.
You cannot mount TO anything except a mountpoint (aka directory)
You cannot use bind to mount something prefixed with a /dev pathname--ie you can only mount directories to directories

Well shiver me timbers. I just tried this and it worked.

Code:

mount --bind /etc /var/db
ls /var/db
a2ps.cfg              info-dir                     ppp
a2ps-site.cfg         init.d                       printcap
acpi                  initlog.conf                 printer
activeheartstylerc    inittab                      product.id
adjtime               inputrc                      profile
...

My /etc directory is not a separate partition. This is great. Now I can cross mount any number of directories to other directories.

There's always more to learn.

macemoneta · 09-02-2007, 07:11 PM

The functionality of 'mount --bind' is the equivalent of just performing a symbolic or hard link, with two exceptions that I can think of:

- A 'mount --bind' will work for a chroot jail, while a symbolic link will not.
- A hard link will work for a chroot jail, but not if the link is to another filesystem.

Unless you need that specific functionality, links work just as well.

pixellany · 09-02-2007, 07:25 PM

Quote:

This is great. Now I can cross mount any number of directories to other directories.

Sounds like a really great way to confuse yourself...I raise you one: