Power failure: file damage? Post: 302895040

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Top Forums UNIX for Dummies Questions & Answers Power failure: file damage? Post 302895040 by bakunin on Friday 28th of March 2014 10:06:33 AM

03-28-2014

Registered User

Quote:

Originally Posted by raylier

But is it possible that there are damaged files I don't know of but can cause trouble later on?

Yes, there is a very remote chance of that having happened, but it is not at all likely.

Most Unix systems today use a "journaling filesystem" of some sort or other and these are quite robust when it comes to unexpected power loss.

At the startup a system will notice that a filesystem was not properly closed during the shutdown before in such a case and initiate a filesystem check. While older FSes would have a (ever diminishing) chance of such a check not being successful (SUNs sfs, for instance, was famous for the high rate of this happening) or some files being beyond repair modern FSes - and especially journaling FSes - run a very low risk in this regard. Usually you see something like "replaying log" during startup and the time that takes is barely noticeable.

I hope this helps.

bakunin

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LEARN ABOUT XFREE86

e2undo

E2UNDO(8)						      System Manager's Manual							 E2UNDO(8)

NAME

       e2undo - Replay an undo log for an ext2/ext3/ext4 filesystem

SYNOPSIS

       e2undo [ -f ] [ -h ] [ -n ] [ -o offset ] [ -v ] [ -z undo_file ] undo_log device

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.

OPTIONS

       -f     Normally, e2undo will check the filesystem superblock to make sure the undo log matches with the filesystem on the device.  If  they
	      do not match, e2undo will refuse to apply the undo log as a safety mechanism.  The -f option disables this safety mechanism.

       -h     Display a usage message.

       -n     Dry-run; do not actually write blocks back to the filesystem.

       -o offset
	      Specify the filesystem's offset (in bytes) from the beginning of the device or file.

       -v     Report which block we're currently replaying.

       -z undo_file
	      Before  overwriting  a  file  system  block,  write  the old contents of the block to an undo file.  This undo file can be used with
	      e2undo(8) to restore the old contents of the file system should something go wrong.  If the empty string is passed as the  undo_file
	      argument,  the  undo file will be written to a file named e2undo-device.e2undo in the directory specified via the E2FSPROGS_UNDO_DIR
	      environment variable.

	      WARNING: The undo file cannot be used to recover from a power or system crash.

AUTHOR

       e2undo was written by Aneesh Kumar K.V. (aneesh.kumar@linux.vnet.ibm.com)

AVAILABILITY

       e2undo is part of the e2fsprogs package and is available from http://e2fsprogs.sourceforge.net.

SEE ALSO

       mke2fs(8), tune2fs(8)

E2fsprogs version 1.44.1					    March 2018								 E2UNDO(8)