|
HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
NAME | SYNOPSIS | DESCRIPTION | OPTIONS | RAW IMAGE FILES | QCOW2 IMAGE FILES | OFFSETS | AUTHOR | AVAILABILITY | SEE ALSO | COLOPHON |
|
|
|
E2IMAGE(8) System Manager's Manual E2IMAGE(8)
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 (tytso@mit.edu).
e2image is part of the e2fsprogs package and is available from
http://e2fsprogs.sourceforge.net.
dumpe2fs(8), debugfs(8) e2fsck(8)
This page is part of the e2fsprogs (utilities for ext2/3/4
filesystems) project. Information about the project can be found
at ⟨http://e2fsprogs.sourceforge.net/⟩. It is not known how to
report bugs for this man page; if you know, please send a mail to
man-pages@man7.org. This page was obtained from the project's
upstream Git repository
⟨git://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git⟩ on
2024-06-14. (At that time, the date of the most recent commit
that was found in the repository was 2024-05-20.) If you
discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for
the page, or you have corrections or improvements to the
information in this COLOPHON (which is not part of the original
manual page), send a mail to man-pages@man7.org
E2fsprogs version 1.47.1 May 2024 E2IMAGE(8)
Pages that refer to this page: e2fsck(8)
|
HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|