misc/e2image.8.in

   1 .\" -*- nroff -*-
   2 .\" Copyright 2001 by Theodore Ts'o.  All Rights Reserved.
   3 .\" This file may be copied under the terms of the GNU Public License.
   4 .\"
   5 .TH E2IMAGE 8 "@E2FSPROGS_MONTH@ @E2FSPROGS_YEAR@" "E2fsprogs version @E2FSPROGS_VERSION@"
   6 .SH NAME
   7 e2image \- Save critical ext2/ext3/ext4 filesystem metadata to a file
   8 .SH SYNOPSIS
   9 .B e2image
  10 [
  11 .B \-rsIQa
  12 ]
  13 .I device
  14 .I image-file
  15 .SH DESCRIPTION
  16 The
  17 .B e2image
  18 program will save critical ext2, ext3, or ext4 filesystem metadata located on
  19 .I device
  20 to a file specified by
  21 .IR image-file .
  22 The image file may be examined by
  23 .B dumpe2fs
  24 and
  25 .BR  debugfs ,
  26 by using the
  27 .B \-i
  28 option to those programs.  This can assist an expert in
  29 recovering catastrophically corrupted filesystems.  In the future,
  30 e2fsck will be enhanced to be able to use the image file to help
  31 recover a badly damaged filesystem.
  32 .PP
  33 If
  34 .I image-file
  35 is \-, then the output of
  36 .B e2image
  37 will be sent to standard output, so that the output can be piped to
  38 another program, such as
  39 .BR gzip (1).
  40 (Note that this is currently only supported when
  41 creating a raw image file using the
  42 .B \-r
  43 option, since the process of creating a normal image file, or QCOW2
  44 image currently
  45 requires random access to the file, which cannot be done using a
  46 pipe.  This restriction will hopefully be lifted in a future version of
  47 .BR e2image .)
  48 .PP
  49 It is a very good idea to create image files for all of
  50 filesystems on a system and save the partition
  51 layout (which can be generated using the
  52 .B fdisk \-l
  53 command) at regular intervals --- at boot time, and/or every week or so.
  54 The image file should be stored on some filesystem other than
  55 the filesystem whose data it contains, to ensure that this data is
  56 accessible in the case where the filesystem has been badly damaged.
  57 .PP
  58 To save disk space,
  59 .B e2image
  60 creates the image file as a sparse file, or in QCOW2 format.
  61 Hence, if the sparse image file
  62 needs to be copied to another location, it should
  63 either be compressed first or copied using the
  64 .B \-\-sparse=always
  65 option to the GNU version of
  66 .BR cp .
  67 This does not apply to the QCOW2 image, which is not sparse.
  68 .PP
  69 The size of an ext2 image file depends primarily on the size of the
  70 filesystems and how many inodes are in use.  For a typical 10 gigabyte
  71 filesystem, with 200,000 inodes in use out of 1.2 million inodes, the
  72 image file will be approximately 35 megabytes; a 4 gigabyte filesystem with
  73 15,000 inodes in use out of 550,000 inodes will result in a 3 megabyte
  74 image file.  Image files tend to be quite
  75 compressible; an image file taking up 32 megabytes of space on
  76 disk will generally compress down to 3 or 4 megabytes.
  77 .PP
  78 .SH RESTORING FILESYSTEM METADATA USING AN IMAGE FILE
  79 .PP
  80 The
  81 .B \-I
  82 option will cause e2image to install the metadata stored in the image
  83 file back to the device.  It can be used to restore the filesystem metadata
  84 back to the device in emergency situations.
  85 .PP
  86 .B WARNING!!!!
  87 The
  88 .B \-I
  89 option should only be used as a desperation measure when other
  90 alternatives have failed.  If the filesystem has changed since the image
  91 file was created, data
  92 .B will
  93 be lost.  In general, you should make a full image
  94 backup of the filesystem first, in case you wish to try other recovery
  95 strategies afterwards.
  96 .PP
  97 .SH RAW IMAGE FILES
  98 The
  99 .B \-r
 100 option will create a raw image file instead of a normal image file.
 101 A raw image file differs
 102 from a normal image file in two ways.  First, the filesystem metadata is
 103 placed in the proper position so that e2fsck, dumpe2fs, debugfs,
 104 etc.\& can be run directly on the raw image file.  In order to minimize
 105 the amount of disk space consumed by a raw image file, the file is
 106 created as a sparse file.  (Beware of copying or
 107 compressing/decompressing this file with utilities that don't understand
 108 how to create sparse files; the file will become as large as the
 109 filesystem itself!)  Secondly, the raw image file also includes indirect
 110 blocks and directory blocks, which the standard image file does not have,
 111 although this may change in the future.
 112 .PP
 113 Raw image files are sometimes used when sending filesystems to the maintainer
 114 as part of bug reports to e2fsprogs.  When used in this capacity, the
 115 recommended command is as follows (replace hda1 with the appropriate device):
 116 .PP
 117 .br
 118         \fBe2image \-r /dev/hda1 \- | bzip2 > hda1.e2i.bz2\fR
 119 .PP
 120 This will only send the metadata information, without any data blocks.
 121 However, the filenames in the directory blocks can still reveal
 122 information about the contents of the filesystem that the bug reporter
 123 may wish to keep confidential.  To address this concern, the
 124 .B \-s
 125 option can be specified.  This will cause
 126 .B e2image
 127 to scramble directory entries and zero out any unused portions
 128 of the directory blocks before writing the image file.  However,
 129 the
 130 .B \-s
 131 option will prevent analysis of problems related to hash-tree indexed
 132 directories.
 133 .PP
 134 Note that this will work even if you substitute "/dev/hda1" for another raw
 135 disk image, or QCOW2 image previously created by
 136 .BR e2image .
 137 .PP
 138 .SH QCOW2 IMAGE FILES
 139 The
 140 .B \-Q
 141 option will create a QCOW2 image file instead of a normal, or raw image file.
 142 A QCOW2 image contains all the information the raw image does, however unlike
 143 the raw image it is not sparse. The QCOW2 image minimize the amount of disk
 144 space by storing data in special format with pack data closely together, hence
 145 avoiding holes while still minimizing size.
 146 .PP
 147 In order to send filesystem to the maintainer as a part of bug report to
 148 e2fsprogs, use following commands (replace hda1 with the appropriate device):
 149 .PP
 150 .br
 151 \       \fBe2image \-Q /dev/hda1 hda1.qcow2\fR
 152 .br
 153 \       \fBbzip2 -z hda1.qcow2\fR
 154 .PP
 155 This will only send the metadata information, without any data blocks.
 156 However, the filenames in the directory blocks can still reveal
 157 information about the contents of the filesystem that the bug reporter
 158 may wish to keep confidential.  To address this concern, the
 159 .B \-s
 160 option can be specified.  This will cause
 161 .B e2image
 162 to scramble directory entries and zero out any unused portions
 163 of the directory blocks before writing the image file.  However, the
 164 .B \-s
 165 option will prevent analysis of problems related to hash-tree indexed
 166 directories.
 167 .PP
 168 Note that QCOW2 image created by
 169 .B e2image
 170 is regular QCOW2 image and can be processed by tools aware of QCOW2 format
 171 such as for example
 172 .BR qemu-img .
 173 .PP
 174 You can convert a qcow2 image into a raw image with:
 175 .PP
 176 .br
 177 \       \fBe2image \-r hda1.qcow2 hda1.raw\fR
 178 .br
 179 .PP
 180 This can be useful to write a qcow2 image containing all data to a
 181 sparse image file where it can be loop mounted, or to a disk partition.
 182 Note that this may not work with qcow2 images not generated by e2image.
 183 .PP
 184 .SH INCLUDING DATA
 185 Normally
 186 .B e2image
 187 only includes fs metadata, not regular file data.  The
 188 .B \-a
 189 option can be specified to include all data.  This will
 190 give an image that is suitable to use to clone the entire FS or
 191 for backup purposes.  Note that this option only works with the
 192 raw or QCOW2 formats.
 193 .PP
 194 .SH AUTHOR
 195 .B e2image
 196 was written by Theodore Ts'o (tytso@mit.edu).
 197 .SH AVAILABILITY
 198 .B e2image
 199 is part of the e2fsprogs package and is available from
 200 http://e2fsprogs.sourceforge.net.
 201 .SH SEE ALSO
 202 .BR dumpe2fs (8),
 203 .BR debugfs (8)
 204