NAME¶
e2image - Save critical ext2/ext3/ext4 filesystem metadata to a file
SYNOPSIS¶
e2image [
-rsI ]
device image-file
DESCRIPTION¶
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, or QCOW2 image 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, or
in QCOW2 format. Hence, if the sparse 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. This does not
apply to the QCOW2 image, which is not sparse.
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.
RAW IMAGE FILES¶
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.
Note that this will work even if you substitute "/dev/hda1" for
another raw disk image, or QCOW2 image previously created by
e2image.
QCOW2 IMAGE FILES¶
The
-Q option will create a QCOW2 image file instead of a normal, or raw
image file. A QCOW2 image contains all the information the raw image does,
however unlike the raw image it is not sparse. The QCOW2 image minimize the
amount of disk space by storing data in special format with pack data closely
together, hence avoiding holes while still minimizing size.
In order to send filesystem to the maintainer as a part of bug report to
e2fsprogs, use following commands (replace hda1 with the appropriate device):
e2image -Q /dev/hda1 hda1.qcow2
bzip2 -z hda1.qcow2
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.
Note that QCOW2 image created by
e2image is regular QCOW2 image and can
be processed by tools aware of QCOW2 format such as for example
qemu-img.
AUTHOR¶
e2image was written by Theodore Ts'o (tytso@mit.edu).
AVAILABILITY¶
e2image is part of the e2fsprogs package and is available from
http://e2fsprogs.sourceforge.net.
SEE ALSO¶
dumpe2fs(8),
debugfs(8)
