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Topic: unionfs help corner, Let's talk about it a bit.

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Zucca

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Posts: 524
Joined: Feb. 2006

Posted: Sep. 05 2006,07:34

Ok. I've read some information about unionfs.
But some open questions still remain.

Creating a tmpfs partition and merging it with another partition that already exist and contains files:
Ok. I have a tmpfs mount mounted to /tmpbin and also a root mount (mounted to / ofcourse) formatted to... let's say reiserfs (doesn't really matter what format).
Now I want that my /bin directory could be writeable but not permanently.
So I decide to mount /tmpbin over /bin using unionfs.

I wonder if it is possible?

Code Sample

mount -t unionfs -o dirs=/tmpbin=rw:/bin=ro unionfs /bin

Ok. Let's assume it worked just fine.
What if I delete a file that was originally on /bin? Does some special file on /tmpbin tell that the file is deleted (until reboot)? More simplier: How does my system know that the file is deleted while it still exists in ro area physically but invisible to system.

I'll be posting more questions later and also some anvers if I happen to find them.

Any urls refering to basic unionfs quide are very velcome.

--------------
Do you have it? - http://dy.fi/mak

Zucca

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Posts: 524
Joined: Feb. 2006

Posted: Sep. 11 2006,14:28

Quote

Unionfs is a stackable filesystem, allowing you to "merge" several different filesystems together.

Ok. So it seems that unionfs is not actually a filesystem (?). I is just a mount that combines different filesystems together.

--------------
Do you have it? - http://dy.fi/mak

dmizzel

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Posts: 112
Joined: April 2005

Posted: Sep. 12 2006,00:12

This link is for unionfs as it is used in mac osx. I found it informative in a general overview sort of way. I don't know if it applies, or is what you're looking for.

http://rentzsch.com/macosx/unionFilesystems

Zucca

Group: Members
Posts: 524
Joined: Feb. 2006

Posted: Sep. 18 2006,14:36

Thanks. That document has few intresting points. =)

--------------
Do you have it? - http://dy.fi/mak

Zucca

Group: Members
Posts: 524
Joined: Feb. 2006

Posted: Sep. 18 2006,14:47

Quote

In FreeBSD/NetBSD, deleting a file in the base system should not really delete this file, but rather add a 'whiteout' file to the overlay. If the file system of the overlay does not support whiteout files, deleting files in the base system should not be possible at all.

Ok. Then I'll like to know what filesystems support these whiteout files?

--------------
Do you have it? - http://dy.fi/mak

5 replies since Sep. 05 2006,07:34

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