mirror of
https://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git
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75dd3c47c4
badblocks.c: Add -B and -X to usage text. chattr.1.in: Add P to list of settable attributes. e2image.8.in, e2image.c: Remove superfluous mention of -r option. e2undo.8.in, e2undo.c: Add description for -z to man page and add -o and -z to synopsis and usage text. e4crypt.8.in: Add -p pad option to relevant command descriptions. lsattr.1.in: Fix typo. mke2fs.8.in: Add -C to synopsis. Add MKE2FS_DEVICE_PHYS_SECTSIZE description and update MKE2FS_DEVICE_SECTSIZE description. mke2fs.conf.5.in: Add devices stanza summary. Remove base_features and default_features descriptions from defaults section, as they are already described in fs_types section. Move enable_periodic_fsck and force_undo to fs_types section, as they can be set per filesystem type. Add missing lazy_journal_init and hugefiles_dir descriptions. tune2fs.8.in: Remove unsupported -p option and deprecated -s option. Add 64bit, ea_inode, large_dir, and metadata_csum_seed descriptions. tune2fs.c: Remove unsupported -p option from usage text. Add mmp_update_interval to extended option usage text. resize/main.c: Add -S option to usage text. Signed-off-by: Tyson Nottingham <tgnottingham@gmail.com> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
286 lines
9.0 KiB
Groff
286 lines
9.0 KiB
Groff
.\" -*- nroff -*-
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.\" Copyright 2001 by Theodore Ts'o. All Rights Reserved.
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.\" This file may be copied under the terms of the GNU Public License.
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.\"
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.TH E2IMAGE 8 "@E2FSPROGS_MONTH@ @E2FSPROGS_YEAR@" "E2fsprogs version @E2FSPROGS_VERSION@"
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.SH NAME
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e2image \- Save critical ext2/ext3/ext4 filesystem metadata to a file
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.SH SYNOPSIS
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.B e2image
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[
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.B \-r|Q
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]
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[
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.B \-f
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]
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.I device
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.I image-file
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.br
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.B e2image
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.B \-I
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.I device
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.I image-file
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.br
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.B e2image
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.B \-ra
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[
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.B \-cfnp
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]
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[
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.B \-o
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.I src_offset
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]
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[
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.B \-O
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.I dest_offset
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]
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.I src_fs
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[
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.I dest_fs
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]
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.SH DESCRIPTION
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The
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.B e2image
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program will save critical ext2, ext3, or ext4 filesystem metadata located on
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.I device
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to a file specified by
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.IR image-file .
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The image file may be examined by
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.B dumpe2fs
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and
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.BR debugfs ,
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by using the
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.B \-i
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option to those programs. This can assist an expert in
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recovering catastrophically corrupted filesystems. In the future,
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e2fsck will be enhanced to be able to use the image file to help
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recover a badly damaged filesystem.
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.PP
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When saving an e2image for debugging purposes, using either the
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.B \-r
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or
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.B \-Q
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options, the filesystem must be unmounted or be mounted read/only, in order
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for the image file to be in a consistent state. This requirement can be
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overridden using the
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.B \-f
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option, but the resulting image file is very likely not going to be useful.
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.PP
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If
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.I image-file
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is \-, then the output of
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.B e2image
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will be sent to standard output, so that the output can be piped to
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another program, such as
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.BR gzip (1).
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(Note that this is currently only supported when
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creating a raw image file using the
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.B \-r
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option, since the process of creating a normal image file, or QCOW2
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image currently
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requires random access to the file, which cannot be done using a
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pipe. This restriction will hopefully be lifted in a future version of
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.BR e2image .)
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.PP
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It is a very good idea to create image files for all of
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filesystems on a system and save the partition
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layout (which can be generated using the
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.B fdisk \-l
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command) at regular intervals --- at boot time, and/or every week or so.
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The image file should be stored on some filesystem other than
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the filesystem whose data it contains, to ensure that this data is
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accessible in the case where the filesystem has been badly damaged.
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.PP
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To save disk space,
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.B e2image
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creates the image file as a sparse file, or in QCOW2 format.
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Hence, if the sparse image file
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needs to be copied to another location, it should
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either be compressed first or copied using the
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.B \-\-sparse=always
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option to the GNU version of
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.BR cp .
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This does not apply to the QCOW2 image, which is not sparse.
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.PP
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The size of an ext2 image file depends primarily on the size of the
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filesystems and how many inodes are in use. For a typical 10 gigabyte
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filesystem, with 200,000 inodes in use out of 1.2 million inodes, the
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image file will be approximately 35 megabytes; a 4 gigabyte filesystem with
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15,000 inodes in use out of 550,000 inodes will result in a 3 megabyte
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image file. Image files tend to be quite
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compressible; an image file taking up 32 megabytes of space on
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disk will generally compress down to 3 or 4 megabytes.
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.PP
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.SH RESTORING FILESYSTEM METADATA USING AN IMAGE FILE
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.PP
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The
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.B \-I
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option will cause e2image to install the metadata stored in the image
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file back to the device. It can be used to restore the filesystem metadata
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back to the device in emergency situations.
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.PP
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.B WARNING!!!!
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The
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.B \-I
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option should only be used as a desperation measure when other
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alternatives have failed. If the filesystem has changed since the image
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file was created, data
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.B will
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be lost. In general, you should make a full image
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backup of the filesystem first, in case you wish to try other recovery
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strategies afterwards.
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.PP
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.SH RAW IMAGE FILES
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The
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.B \-r
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option will create a raw image file instead of a normal image file.
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A raw image file differs
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from a normal image file in two ways. First, the filesystem metadata is
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placed in the proper position so that e2fsck, dumpe2fs, debugfs,
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etc.\& can be run directly on the raw image file. In order to minimize
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the amount of disk space consumed by a raw image file, the file is
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created as a sparse file. (Beware of copying or
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compressing/decompressing this file with utilities that don't understand
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how to create sparse files; the file will become as large as the
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filesystem itself!) Secondly, the raw image file also includes indirect
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blocks and directory blocks, which the standard image file does not have,
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although this may change in the future.
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.PP
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Raw image files are sometimes used when sending filesystems to the maintainer
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as part of bug reports to e2fsprogs. When used in this capacity, the
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recommended command is as follows (replace hda1 with the appropriate device):
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.PP
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.br
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\fBe2image \-r /dev/hda1 \- | bzip2 > hda1.e2i.bz2\fR
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.PP
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This will only send the metadata information, without any data blocks.
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However, the filenames in the directory blocks can still reveal
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information about the contents of the filesystem that the bug reporter
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may wish to keep confidential. To address this concern, the
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.B \-s
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option can be specified. This will cause
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.B e2image
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to scramble directory entries and zero out any unused portions
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of the directory blocks before writing the image file. However,
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the
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.B \-s
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option will prevent analysis of problems related to hash-tree indexed
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directories.
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.PP
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Note that this will work even if you substitute "/dev/hda1" for another raw
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disk image, or QCOW2 image previously created by
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.BR e2image .
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.PP
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.SH QCOW2 IMAGE FILES
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The
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.B \-Q
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option will create a QCOW2 image file instead of a normal, or raw image file.
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A QCOW2 image contains all the information the raw image does, however unlike
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the raw image it is not sparse. The QCOW2 image minimize the amount of disk
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space by storing data in special format with pack data closely together, hence
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avoiding holes while still minimizing size.
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.PP
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In order to send filesystem to the maintainer as a part of bug report to
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e2fsprogs, use following commands (replace hda1 with the appropriate device):
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.PP
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.br
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\ \fBe2image \-Q /dev/hda1 hda1.qcow2\fR
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.br
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\ \fBbzip2 -z hda1.qcow2\fR
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.PP
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This will only send the metadata information, without any data blocks.
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However, the filenames in the directory blocks can still reveal
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information about the contents of the filesystem that the bug reporter
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may wish to keep confidential. To address this concern, the
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.B \-s
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option can be specified. This will cause
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.B e2image
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to scramble directory entries and zero out any unused portions
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of the directory blocks before writing the image file. However, the
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.B \-s
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option will prevent analysis of problems related to hash-tree indexed
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directories.
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.PP
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Note that QCOW2 image created by
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.B e2image
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is regular QCOW2 image and can be processed by tools aware of QCOW2 format
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such as for example
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.BR qemu-img .
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.PP
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You can convert a qcow2 image into a raw image with:
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.PP
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.br
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\ \fBe2image \-r hda1.qcow2 hda1.raw\fR
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.br
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.PP
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This can be useful to write a qcow2 image containing all data to a
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sparse image file where it can be loop mounted, or to a disk partition.
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Note that this may not work with qcow2 images not generated by e2image.
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.PP
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.SH INCLUDING DATA
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Normally
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.B e2image
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only includes fs metadata, not regular file data. The
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.B \-a
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option can be specified to include all data. This will
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give an image that is suitable to use to clone the entire FS or
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for backup purposes. Note that this option only works with the
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raw or QCOW2 formats. The
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.B \-p
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switch may be given to show progress. If the file system is being
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cloned to a flash-based storage device (where reads are very fast and
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where it is desirable to avoid unnecessary writes to reduce write wear
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on the device), the
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.B \-c
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option which cause e2image to try reading a block from the destination
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to see if it is identical to the block which
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.B e2image
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is about to copy. If the block is already the same, the write can be
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skipped. The
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.B \-n
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option will cause all of the writes to be no-ops, and print the blocks
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that would have been written.
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.PP
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.SH OFFSETS
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Normally a filesystem starts at the beginning of a partition, and
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.B e2image
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is run on the partition. When working with image files, you don't
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have the option of using the partition device, so you can specify
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the offset where the filesystem starts directly with the
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.B \-o
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option. Similarly the
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.B \-O
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option specifies the offset that should be seeked to in the destination
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before writing the filesystem.
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.PP
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For example, if you have a
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.B dd
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image of a whole hard drive that contains an ext2 fs in a partition
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starting at 1 MiB, you can clone that fs with:
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.PP
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.br
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\ \fBe2image \-aro 1048576 img /dev/sda1\fR
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.br
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.PP
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Or you can clone a fs into an image file, leaving room in the first
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MiB for a partition table with:
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.PP
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.br
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\ \fBe2image -arO 1048576 /dev/sda1 img\fR
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.br
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.PP
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If you specify at least one offset, and only one file, an in-place
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move will be performed, allowing you to safely move the filesystem
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from one offset to another.
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.SH AUTHOR
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.B e2image
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was written by Theodore Ts'o (tytso@mit.edu).
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.SH AVAILABILITY
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.B e2image
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is part of the e2fsprogs package and is available from
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http://e2fsprogs.sourceforge.net.
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.SH SEE ALSO
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.BR dumpe2fs (8),
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.BR debugfs (8)
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