e2image - Save critical ext2/ext3/ext4 file system metadata to a file
e2image [
-r|
-Q [
-af]] [
-b superblock
] [
-B blocksize ] [
-cnps ] [
-o
src_offset ] [
-O dest_offset ]
device
image-file
e2image -I device image-file
The
e2image program will save critical ext2, ext3, or ext4 file system
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 file systems.
It is a very good idea to create image files for all file systems 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 file system other than the file
system whose data it contains, to ensure that this data is accessible in the
case where the file system 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(1). 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 file systems
and how many inodes are in use. For a typical 10 Gigabyte file system, with
200,000 inodes in use out of 1.2 million inodes, the image file will be
approximately 35 Megabytes; a 4 Gigabyte file system 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.
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.
- -a
- Include file data in the image file. Normally
e2image only includes fs metadata, not regular file data. This
option will produce an image that is suitable to use to clone the entire
FS or for backup purposes. Note that this option only works with the raw
(-r) or QCOW2 (-Q) formats. In conjunction with the
-r option it is possible to clone all and only the used blocks of
one file system to another device/image file.
-
-b superblock
- Get image from partition with broken primary superblock by
using the superblock located at file system block number
superblock. The partition is copied as-is including broken primary
superblock.
-
-B blocksize
- Set the file system blocksize in bytes. Normally,
e2image will search for the superblock at various different block
sizes in an attempt to find the appropriate blocksize. This search can be
fooled in some cases. This option forces e2fsck to only try locating the
superblock with a particular blocksize. If the superblock is not found,
e2image will terminate with a fatal error.
- -c
- Compare each block to be copied from the source
device to the corresponding block in the target image-file.
If both are already the same, the write will be skipped. This is useful if
the file system is being cloned to a flash-based storage device (where
reads are very fast and where it is desirable to avoid unnecessary writes
to reduce write wear on the device).
- -f
- Override the read-only requirement for the source file
system when saving the image file using the -r and -Q
options. Normally, if the source file system is in use, the resulting
image file is very likely not going to be useful. In some cases where the
source file system is in constant use this may be better than no image at
all.
- -I
- install the metadata stored in the image file back to the
device. It can be used to restore the file system 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 file system has changed
since the image file was created, data
will be lost. In general, you
should make another full image backup of the file system first, in case you
wish to try other recovery strategies afterward.
- -n
- Cause all image writes to be skipped, and instead only
print the block numbers that would have been written.
-
-o src_offset
- Specify offset of the image to be read from the start of
the source device in bytes. See OFFSETS for more
details.
-
-O tgt_offset
- Specify offset of the image to be written from the start of
the target image-file in bytes. See OFFSETS for more
details.
- -p
- Show progress of image-file creation.
- -Q
- Create a QCOW2-format image file instead of a normal image
file, suitable for use by virtual machine images, and other tools that can
use the .qcow image format. See QCOW2 IMAGE FILES below for
details.
- -r
- Create a raw image file instead of a normal image file. See
RAW IMAGE FILES below for details.
- -s
- Scramble directory entries and zero out unused portions of
the directory blocks in the written image file to avoid revealing
information about the contents of the file system. However, this will
prevent analysis of problems related to hash-tree indexed directories.
The
-r option will create a raw image file, which differs from a normal
image file in two ways. First, the file system metadata is placed in the same
relative offset within
image-file as it is in the
device so that
debugfs(8),
dumpe2fs(8),
e2fsck(8),
losetup(8),
etc. and can be run directly on the raw image file. In order to minimize the
amount of disk space consumed by the raw image file, it 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 file system itself!) Secondly, the raw image file also includes
indirect blocks and directory blocks, which the standard image file does not
have.
Raw image files are sometimes used when sending file systems 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 for your system):
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 file system that the bug reporter may wish to keep
confidential. To address this concern, the
-s option can be specified
to scramble the filenames in the image.
Note that this will work even if you substitute
/dev/hda1 for another raw
disk image, or QCOW2 image previously created by
e2image.
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 space used by the image by storing it in special format which packs
data closely together, hence avoiding holes while still minimizing size.
In order to send file system to the maintainer as a part of bug report to
e2fsprogs, use following commands (replace
hda1 with the appropriate
device for your system):
e2image -Q /dev/hda1 hda1.qcow2
bzip2 -z hda1.qcow2
This will only send the metadata information, without any data blocks. As
described for
RAW IMAGE FILES the
-s option can be specified to
scramble the file system names in the image.
Note that the QCOW2 image created by
e2image is a regular QCOW2 image and
can be processed by tools aware of QCOW2 format such as for example
qemu-img.
You can convert a .qcow2 image into a raw image with:
e2image -r hda1.qcow2 hda1.raw
This can be useful to write a QCOW2 image containing all data to a sparse image
file where it can be loop mounted, or to a disk partition. Note that this may
not work with QCOW2 images not generated by e2image.
Normally a file system starts at the beginning of a partition, and
e2image is run on the partition. When working with image files, you
don't have the option of using the partition device, so you can specify the
offset where the file system starts directly with the
-o option.
Similarly the
-O option specifies the offset that should be seeked to
in the destination before writing the file system.
For example, if you have a
dd image of a whole hard drive that contains
an ext2 fs in a partition starting at 1 MiB, you can clone that image to a
block device with:
e2image -aro 1048576 img /dev/sda1
Or you can clone a file system from a block device into an image file, leaving
room in the first MiB for a partition table with:
e2image -arO 1048576 /dev/sda1 img
If you specify at least one offset, and only one file, an in-place move will be
performed, allowing you to safely move the file system from one offset to
another.
e2image was written by Theodore Ts'o (
[email protected]).
e2image is part of the e2fsprogs package and is available from
http://e2fsprogs.sourceforge.net.
dumpe2fs(8),
debugfs(8) e2fsck(8)