filesystem owner and permissions--where stored?

pixellany · 05-16-2012, 08:31 AM

I'm doing a bit of re-learning---please bear with me.

If I have an unmounted partition (file system, to be more precise), I cannot find a way of knowing the owner, permissions, etc.

If I mount and then change the attributes (chown, chmod, etc.), then that info stays with the partition after unmounting and re-mounting.

So---where is this info stored, and is it accessible without mounting?

anon258 · 05-16-2012, 08:56 AM

If that partittion is for example /dev/sda1 you can find in it permission information

pixellany · 05-16-2012, 10:05 AM

Quote:

Originally Posted by Fantastic

If that partittion is for example /dev/sda1 you can find in it permission information

If it's not mounted?

pan64 · 05-16-2012, 11:35 AM

the filesystem has no owner, usually it can be mounted by the root of a system. The owners, permissions and attributes of the files on the filesystem are stored within the filesystem and are can only be read by the driver of that filesystem (in short: they are filesystem specific data stored on the disk)

pixellany · 05-17-2012, 05:29 AM

Quote:

Originally Posted by pan64

the filesystem has no owner...

Here's the exact scenario: I created a partition as root---no files. When mounted, the mount point showed ownership by root. Also, when mounted, the ownership (and permissions) could be changed. Thus, the filesystem (volume) has owner/permission attributes just like a regular file. I assume that all of this is stored with the filesystem.

pan64 · 05-17-2012, 05:44 AM

no, the filesystem has no ownership, you can take that disk and give it to me and I will be able to mount and read that without knowing about your config.
when you mount a partition you will define the owner. usually it is the root. All the files/dirs stored inside can only be accessed by the filesystem's driver.

colucix · 05-17-2012, 06:08 AM

In ext2/ext3/ext4 filesystem, information about file type, file size, permissions, extended attributes, number of hard links and so on are stored in the inode of the file. Here is an interesting article about the structure of an ext4 filesystem and how to retrieve information stored in the inodes even from unmounted filesystems (if I understand well). They use some commands like istat or fsstat that are provided by the Sleuth Kit. Have fun!

Edit: FYI the other parts of the featured article are listed here.

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