Ubuntu Manpage: e2image - Save critical ext2/ext3/ext4 filesystem metadata to a file

Provided by: e2fsprogs_1.45.5-2ubuntu1.2_amd64

NAME

       e2image - Save critical ext2/ext3/ext4 filesystem metadata to a file

SYNOPSIS

       e2image [ -r|-Q ] [ -f ] [ -b superblock ] [ -B blocksize ] device image-file
       e2image -I device image-file
       e2image -ra [ -cfnp ] [ -o src_offset ] [ -O dest_offset ] src_fs [ dest_fs ]

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.

When saving an e2image for debugging purposes, using either the -r or -Q options, the
filesystem must be unmounted or be mounted read/only, in order for the image file to be in
a consistent state. This requirement can be overridden using the -f option, but the
resulting image file is very likely not going to be useful.

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.

RESTORING FILESYSTEM METADATA USING AN IMAGE FILE

       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.

Option -b superblock can be used to get image from partition with broken primary
superblock. The partition is copied as-is including broken primary superblock.

Option -B blocksize can be used to set superblock block size. Normally, e2fsck 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 at a particular blocksize. If the superblock is not found, e2fsck
will terminate with a fatal error.

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

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.

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.

Options -b superblock and -B blocksize can be used same way as for raw images.

INCLUDING DATA

       Normally e2image only includes fs metadata, not regular file data.  The -a option  can  be
       specified  to  include all data.  This will give 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  or
       QCOW2  formats.  The -p switch may be given to show progress.  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), the -c option
       which cause e2image to try reading a block from the destination to see if it is  identical
       to  the block which e2image is about to copy.  If the block is already the same, the write
       can be skipped.  The -n option will cause all of the writes to be no-ops,  and  print  the
       blocks that would have been written.

OFFSETS

       Normally  a  filesystem  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 filesystem starts directly with
       the -o option.  Similarly the -O option specifies the offset that should be seeked  to  in
       the destination before writing the filesystem.

       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 fs with:

            e2image -aro 1048576 img /dev/sda1

       Or you can clone a fs 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 filesystem from one offset to another.

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.