OpenGrok

-*- nroff -*-
Copyright 2001 by Theodore Ts'o. All Rights Reserved.
This file may be copied under the terms of the GNU Public License.

e2image - Save critical ext2/ext3/ext4 filesystem metadata to a file e2image [ -rsI ] device image-file The e2image program will save critical ext2, ext3, or ext4 filesystem metadata located on device to a file specified by image-file . The image file may be examined by dumpe2fs and debugfs , by using the -i option to those programs. This can assist an expert in recovering catastrophically corrupted filesystems. In the future, e2fsck will be enhanced to be able to use the image file to help recover a badly damaged filesystem.

If image-file is -, then the output of e2image will be sent to standard output, so that the output can be piped to another program, such as gzip (1). (Note that this is currently only supported when creating a raw image file using the -r option, since the process of creating a normal image file currently requires random access to the file, which cannot be done using a pipe. This restriction will hopefully be lifted in a future version of e2image .)

It is a very good idea to create image files for all of filesystems on a system and save the partition layout (which can be generated using the fdisk -l command) at regular intervals --- at boot time, and/or every week or so. The image file should be stored on some filesystem other than the filesystem whose data it contains, to ensure that this data is accessible in the case where the filesystem has been badly damaged.

To save disk space, e2image creates the image file as a sparse file. Hence, if the image file needs to be copied to another location, it should either be compressed first or copied using the --sparse=always option to the GNU version of cp .

The size of an ext2 image file depends primarily on the size of the filesystems and how many inodes are in use. For a typical 10 gigabyte filesystem, with 200,000 inodes in use out of 1.2 million inodes, the image file will be approximately 35 megabytes; a 4 gigabyte filesystem with 15,000 inodes in use out of 550,000 inodes will result in a 3 megabyte image file. Image files tend to be quite compressible; an image file taking up 32 megabytes of space on disk will generally compress down to 3 or 4 megabytes.

The -I option will cause e2image to install the metadata stored in the image file back to the device. It can be used to restore the filesystem metadata back to the device in emergency situations.

WARNING!!!! The -I option should only be used as a desperation measure when other alternatives have failed. If the filesystem has changed since the image file was created, data will be lost. In general, you should make a full image backup of the filesystem first, in case you wish to try other recovery strategies afterwards.

The -r option will create a raw image file instead of a normal image file. A raw image file differs from a normal image file in two ways. First, the filesystem metadata is placed in the proper position so that e2fsck, dumpe2fs, debugfs, etc. can be run directly on the raw image file. In order to minimize the amount of disk space consumed by a raw image file, the file is created as a sparse file. (Beware of copying or compressing/decompressing this file with utilities that don't understand how to create sparse files; the file will become as large as the filesystem itself!) Secondly, the raw image file also includes indirect blocks and directory blocks, which the standard image file does not have, although this may change in the future.

Raw image files are sometimes used when sending filesystems to the maintainer as part of bug reports to e2fsprogs. When used in this capacity, the recommended command is as follows (replace hda1 with the appropriate device):

\ e2image -r /dev/hda1 - | bzip2 > hda1.e2i.bz2

This will only send the metadata information, without any data blocks. However, the filenames in the directory blocks can still reveal information about the contents of the filesystem that the bug reporter may wish to keep confidential. To address this concern, the -s option can be specified. This will cause e2image to scramble directory entries and zero out any unused portions of the directory blocks before writing the image file. However, the -s option will prevent analysis of problems related to hash-tree indexed directories.

e2image was written by Theodore Ts'o (tytso (at] mit.edu). e2image is part of the e2fsprogs package and is available from http://e2fsprogs.sourceforge.net. dumpe2fs (8), debugfs (8)