mirror of
https://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git
synced 2024-11-28 12:34:13 +08:00
286 lines
9.0 KiB
Groff
286 lines
9.0 KiB
Groff
.\" -*- nroff -*-
|
|
.\" Copyright 2001 by Theodore Ts'o. All Rights Reserved.
|
|
.\" This file may be copied under the terms of the GNU Public License.
|
|
.\"
|
|
.TH E2IMAGE 8 "@E2FSPROGS_MONTH@ @E2FSPROGS_YEAR@" "E2fsprogs version @E2FSPROGS_VERSION@"
|
|
.SH NAME
|
|
e2image \- Save critical ext2/ext3/ext4 filesystem metadata to a file
|
|
.SH SYNOPSIS
|
|
.B e2image
|
|
[
|
|
.B \-r|Q
|
|
]
|
|
[
|
|
.B \-fr
|
|
]
|
|
.I device
|
|
.I image-file
|
|
.br
|
|
.B e2image
|
|
.B \-I
|
|
.I device
|
|
.I image-file
|
|
.br
|
|
.B e2image
|
|
.B \-ra
|
|
[
|
|
.B \-cfnp
|
|
]
|
|
[
|
|
.B \-o
|
|
.I src_offset
|
|
]
|
|
[
|
|
.B \-O
|
|
.I dest_offset
|
|
]
|
|
.I src_fs
|
|
[
|
|
.I dest_fs
|
|
]
|
|
.SH DESCRIPTION
|
|
The
|
|
.B e2image
|
|
program will save critical ext2, ext3, or ext4 filesystem metadata located on
|
|
.I device
|
|
to a file specified by
|
|
.IR image-file .
|
|
The image file may be examined by
|
|
.B dumpe2fs
|
|
and
|
|
.BR debugfs ,
|
|
by using the
|
|
.B \-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.
|
|
.PP
|
|
When saving an e2image for debugging purposes, using either the
|
|
.B \-r
|
|
or
|
|
.B \-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
|
|
.B \-f
|
|
option, but the resulting image file is very likely not going to be useful.
|
|
.PP
|
|
If
|
|
.I image-file
|
|
is \-, then the output of
|
|
.B e2image
|
|
will be sent to standard output, so that the output can be piped to
|
|
another program, such as
|
|
.BR gzip (1).
|
|
(Note that this is currently only supported when
|
|
creating a raw image file using the
|
|
.B \-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
|
|
.BR e2image .)
|
|
.PP
|
|
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
|
|
.B 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.
|
|
.PP
|
|
To save disk space,
|
|
.B 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
|
|
.B \-\-sparse=always
|
|
option to the GNU version of
|
|
.BR cp .
|
|
This does not apply to the QCOW2 image, which is not sparse.
|
|
.PP
|
|
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.
|
|
.PP
|
|
.SH RESTORING FILESYSTEM METADATA USING AN IMAGE FILE
|
|
.PP
|
|
The
|
|
.B \-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.
|
|
.PP
|
|
.B WARNING!!!!
|
|
The
|
|
.B \-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
|
|
.B 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.
|
|
.PP
|
|
.SH RAW IMAGE FILES
|
|
The
|
|
.B \-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.
|
|
.PP
|
|
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):
|
|
.PP
|
|
.br
|
|
\fBe2image \-r /dev/hda1 \- | bzip2 > hda1.e2i.bz2\fR
|
|
.PP
|
|
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
|
|
.B \-s
|
|
option can be specified. This will cause
|
|
.B e2image
|
|
to scramble directory entries and zero out any unused portions
|
|
of the directory blocks before writing the image file. However,
|
|
the
|
|
.B \-s
|
|
option will prevent analysis of problems related to hash-tree indexed
|
|
directories.
|
|
.PP
|
|
Note that this will work even if you substitute "/dev/hda1" for another raw
|
|
disk image, or QCOW2 image previously created by
|
|
.BR e2image .
|
|
.PP
|
|
.SH QCOW2 IMAGE FILES
|
|
The
|
|
.B \-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.
|
|
.PP
|
|
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):
|
|
.PP
|
|
.br
|
|
\ \fBe2image \-Q /dev/hda1 hda1.qcow2\fR
|
|
.br
|
|
\ \fBbzip2 -z hda1.qcow2\fR
|
|
.PP
|
|
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
|
|
.B \-s
|
|
option can be specified. This will cause
|
|
.B e2image
|
|
to scramble directory entries and zero out any unused portions
|
|
of the directory blocks before writing the image file. However, the
|
|
.B \-s
|
|
option will prevent analysis of problems related to hash-tree indexed
|
|
directories.
|
|
.PP
|
|
Note that QCOW2 image created by
|
|
.B e2image
|
|
is regular QCOW2 image and can be processed by tools aware of QCOW2 format
|
|
such as for example
|
|
.BR qemu-img .
|
|
.PP
|
|
You can convert a qcow2 image into a raw image with:
|
|
.PP
|
|
.br
|
|
\ \fBe2image \-r hda1.qcow2 hda1.raw\fR
|
|
.br
|
|
.PP
|
|
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.
|
|
.PP
|
|
.SH INCLUDING DATA
|
|
Normally
|
|
.B e2image
|
|
only includes fs metadata, not regular file data. The
|
|
.B \-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
|
|
.B \-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
|
|
.B \-c
|
|
option which cause e2image to try reading a block from the destination
|
|
to see if it is identical to the block which
|
|
.B e2image
|
|
is about to copy. If the block is already the same, the write can be
|
|
skipped. The
|
|
.B \-n
|
|
option will cause all of the writes to be no-ops, and print the blocks
|
|
that would have been written.
|
|
.PP
|
|
.SH OFFSETS
|
|
Normally a filesystem starts at the beginning of a partition, and
|
|
.B 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
|
|
.B \-o
|
|
option. Similarly the
|
|
.B \-O
|
|
option specifies the offset that should be seeked to in the destination
|
|
before writing the filesystem.
|
|
.PP
|
|
For example, if you have a
|
|
.B 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:
|
|
.PP
|
|
.br
|
|
\ \fBe2image \-aro 1048576 img /dev/sda1\fR
|
|
.br
|
|
.PP
|
|
Or you can clone a fs into an image file, leaving room in the first
|
|
MiB for a partition table with:
|
|
.PP
|
|
.br
|
|
\ \fBe2image -arO 1048576 /dev/sda1 img\fR
|
|
.br
|
|
.PP
|
|
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.
|
|
.SH AUTHOR
|
|
.B e2image
|
|
was written by Theodore Ts'o (tytso@mit.edu).
|
|
.SH AVAILABILITY
|
|
.B e2image
|
|
is part of the e2fsprogs package and is available from
|
|
http://e2fsprogs.sourceforge.net.
|
|
.SH SEE ALSO
|
|
.BR dumpe2fs (8),
|
|
.BR debugfs (8)
|
|
|