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Full Discussion: Mount point bind issues
Top Forums UNIX for Beginners Questions & Answers Mount point bind issues Post 302994511 by drysdalk on Thursday 23rd of March 2017 04:05:26 PM
Old 03-23-2017
Hi,

Great, glad you got that sorted. One last thing that may disappoint, however. If you're doing this because you're hoping to basically add the free space of the /prod/OpenCSS filesystem to the existing /var/lib/pgsql filesystem...well, then you're out of luck.

That's not how bind mounts work, or what they're for. They're purely for providing an alternative path to access the same content in multiple places, and nothing else. The free space you'll see will be that of the original filesystem, since all the calls are being routed through to the original filesystem - the new one (in your scenario) isn't actually going to be used at all.

For example, watch what happens if I do a bind mount of my /boot filesystem to a new directory, /mnt/misc:

Code:
$ df -h /boot
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1       240M  110M  114M  49% /boot
$ df -h /mnt/misc
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda2       225G  132G   82G  62% /
$ sudo /bin/mount --bind /boot /mnt/misc
$ df -h /boot
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1       240M  110M  114M  49% /boot
$ df -h /mnt/misc
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1       240M  110M  114M  49% /mnt/misc
$ sudo /bin/umount /mnt/misc
$ df -h /boot
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1       240M  110M  114M  49% /boot
$ df -h /mnt/misc
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda2       225G  132G   82G  62% /
$

So as you can see, the disc space and all other properties of the bind mount destination are the same as the source, since in reality all you're doing is providing an additional path for accessing the source, and nothing more.

Hope this helps.
This User Gave Thanks to drysdalk For This Post:
 

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VNDCOMPRESS(1)						    BSD General Commands Manual 					    VNDCOMPRESS(1)

NAME
vndcompress, vnduncompress -- compress/uncompress file system images to/from cloop2 format SYNOPSIS
vndcompress [-cd] disk/fs-image compressed-image [blocksize] vnduncompress [-cd] compressed-image disk/fs-image DESCRIPTION
The vndcompress program compresses an existing file system image into a cloop2 compatible compressed file system image. An optional block- size can be given. If omitted, the default of 64kB is used. The vnduncompress command decompress a cloop2-compressed file system image back into a regular image. The file system images that can be handled are not limited to any specific file system, i.e. it is possible to handle images e.g. in ISO 9660 or UFS/FFS format. File system images in the cloop2 format are intended to be used with the vnd(4) driver in compressed mode as configured by the -z option of the vnconfig(8) program, and later mounted with the appropriate -t option to mount(8). OPTIONS
The following options are available: -c Always compress, even if the program was started as vnduncompress. -d Always uncompress (decompress), even if the program was started as vndcompress. EXIT STATUS
The vndcompress and vnduncompress utilities exit with one of the following values: 0 The operation was performed successfully. 1 An error occurred. EXAMPLES
To compress an existing CD-ROM file system image, run the following commands: # vndcompress netbsd.iso netbsd.izo Note that the resulting compressed image cannot be mounted directly via NetBSD's vnd(4) and mount_cd9660(8) commands any longer. Instead, you will have to use the -z option of vnconfig(8). The following example decompresses an existing CD-ROM file system image that was compressed in the cloop2 format into a regular file that can then be mounted: # vnconfig vnd0 KNOPPIX.iso # mount -t cd9660 -o ro /dev/vnd0d /mnt # vnduncompress /mnt/KNOPPIX/KNOPPIX /var/tmp/knoppix.iso # umount /mnt # vnconfig -u vnd0 # # vnconfig vnd1 /var/tmp/knoppix.iso # mount -t cd9660 -o ro /dev/vnd1d /mnt # ls /mnt .rr_moved cdrom floppy lib opt sbin usr bin dev home mnt proc sys var boot etc initrd none root tmp vmlinuz # umount /mnt # vnconfig -u vnd1 As an alternative, if your vnd(4) was compiled with VND_COMPRESSION, you can use vnconfig(8) to access the cloop-compressed image directly, e.g., # vnconfig vnd0 KNOPPIX.iso # mount -t cd9660 -o ro /dev/vnd0d /mnt # vnconfig -z vnd1 /mnt/KNOPPIX/KNOPPIX # mount -t cd9660 -o ro /dev/vnd1d /mnt2 # ls /mnt2 .rr_moved cdrom floppy lib opt sbin usr bin dev home mnt proc sys var boot etc initrd none root tmp vmlinuz # df /mnt /mnt2 Filesystem Size Used Avail Capacity Mounted on /dev/vnd0a 692M 692M 0B 100% /mnt /dev/vnd1a 1.9G 1.9G 0B 100% /mnt2 # umount /mnt2 # vnconfig -u vnd1 # umount /mnt # vnconfig -u vnd0 Note how the 1.9GB big filesystem on /mnt2 is mounted from the compressed file stored on the 692MB CD mounted on /mnt. To create a com- pressed file system image of an existing directory and mount it, run: # makefs -t ffs include.fs /usr/include # vndcompress include.fs include.fs.cloop2 # vnconfig -z vnd0 include.fs.cloop2 # mount -o ro /dev/vnd0a /mnt # ls /mnt To undo the steps, run: # umount /mnt # vnconfig -u vnd0 # rm /tmp/include.fs.cloop2 # rm /tmp/include.fs SEE ALSO
gzip(1), vnd(4), mount(8), mount_cd9660(8), vnconfig(8) AUTHORS
The vndcompress utility was written by Florian Stoehr <netbsd@wolfnode.de>. The vndcompress manual page was written by Florian Stoehr <netbsd@wolfnode.de> and Hubert Feyrer <hubertf@NetBSD.org>. BSD
December 12, 2005 BSD
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