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

Provided by: e2fsprogs_1.46.5-2ubuntu1.2_amd64

NAME

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

SYNOPSIS

       e2image  [-r|-Q [-af]] [ -b superblock ] [ -B blocksize ] [ -cnps ] [ -o src_offset ] [ -O
       dest_offset ] device image-file
       e2image -I device image-file

DESCRIPTION

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.

OPTIONS

-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.

RAW IMAGE FILES

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.

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  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.

OFFSETS

       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.

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.