I just installed e2fsprogs-1.41.4 and want to know more about the e2undo feature.The manual states can be used to undo a failed operation by an e2fsprogs program via an "undo_log".

(eg.) e2undo undo_log device

Does any one know where & how this "undo_log" gets made? I came across two
interesting optional entries in the mke2fs.conf.5 manual that seem to related to e2undo & its required "undo_log".

(eg.) Default [stanza]

<option> <value>
force undo true (or) false
undo dir none (or) path to existing directory

If value=none, mke2fs will not create an undo file.

Unfortunately that is all I have found out about e2undo. I am thinking that the mke2fs "Undo_log" is made by default given that you can have a value=none for the "undo dir" option shown above. But, even if it is made by default, I will still need to know it's path name when running e2undo.

If anyone can explain exactly how to use e2undo I would appreciate the help. My end is to be able to recover from a failed fsck.ext4 operation. Thank You.

You know this and the links shown there...?

http://e2undel.sourceforge.net/

If that doesn't help come back for links concerning data-recovery tools. Umm, no, please come back anyway and report results in any case .

I don't think e2undel & e2undo are the same thing. I think e2undel is for file recovery & e2undo is used to recover from a failed EXT4 filesystem operation.

Let's say I do a fsck.ext4 -v -f -y /dev/sda1 & for some reason my system refuses to boot after this operation. I believe the utility e2undo
can restore the EXT4 filesystem to its former state.

Here is what the e2fsprogs-1.41.4 manual for e2undo states:

DESCRIPTION
e2undo will replay the undo log undo_log for an ext2/ext3/ext4 filesystem found on device. This can be used to undo a failed operation by an e2fsprogs program.

SYNOPSIS
e2undo [ -f ] undo_log device

Hmm. That's new to me. Anyway, when you create a journal during operation of an ext2 (to create an ext3) the documentation states that the journal will be an invisible (.dot)(?) file until the next reboot and vanish after that.

So just maybe you could find a .undo_log file but more probably it is hidden in some inode. Possibly you could get information using dump2fs... (I have no ext4, so I can't try).

<edit> That implies that the undo_log is created by default and no naming necessary or even possible, so you can probably simply run e2undo since you didn't mention switching the logging off. Why don't you clone the partition ("dd") and give it a go... </edit>

Unfortunately, I haven't got the Ext4 filesystem up & running on my Linux
box yet. I am waiting for the "stable" Mandriva-2009.1 (Spring) distribution to be released & then I'll give EXT4 & KDE4 a test run. It
should be out in May 2009.

Right now, I'm just trying to find out as much as I can about EXT4 so I can avoid & fix future problems. So, if anyone has experience using EXT4
& the e2undo utility, your reply would be appreciated. Thank you.