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 \-r|Q
  12 ]
  13 [
  14 .B \-f
  15 ]
  16 .I device
  17 .I image-file
  18 .br
  19 .B e2image
  20 .B \-I
  21 .I device
  22 .I image-file
  23 .br
  24 .B e2image
  25 .B \-ra
  26 [
  27 .B \-cfnp
  28 ]
  29 [
  30 .B \-o
  31 .I src_offset
  32 ]
  33 [
  34 .B \-O
  35 .I dest_offset
  36 ]
  37 .I src_fs
  38 [
  39 .I dest_fs
  40 ]
  41 .SH DESCRIPTION
  42 The
  43 .B e2image
  44 program will save critical ext2, ext3, or ext4 filesystem metadata located on
  45 .I device
  46 to a file specified by
  47 .IR image-file .
  48 The image file may be examined by
  49 .B dumpe2fs
  50 and
  51 .BR  debugfs ,
  52 by using the
  53 .B \-i
  54 option to those programs.  This can assist an expert in
  55 recovering catastrophically corrupted filesystems.  In the future,
  56 e2fsck will be enhanced to be able to use the image file to help
  57 recover a badly damaged filesystem.
  58 .PP
  59 When saving an e2image for debugging purposes, using either the
  60 .B \-r
  61 or
  62 .B \-Q
  63 options, the filesystem must be unmounted or be mounted read/only, in order
  64 for the image file to be in a consistent state.  This requirement can be
  65 overridden using the
  66 .B \-f
  67 option, but the resulting image file is very likely not going to be useful.
  68 .PP
  69 If
  70 .I image-file
  71 is \-, then the output of
  72 .B e2image
  73 will be sent to standard output, so that the output can be piped to
  74 another program, such as
  75 .BR gzip (1).
  76 (Note that this is currently only supported when
  77 creating a raw image file using the
  78 .B \-r
  79 option, since the process of creating a normal image file, or QCOW2
  80 image currently
  81 requires random access to the file, which cannot be done using a
  82 pipe.  This restriction will hopefully be lifted in a future version of
  83 .BR e2image .)
  84 .PP
  85 It is a very good idea to create image files for all of
  86 filesystems on a system and save the partition
  87 layout (which can be generated using the
  88 .B fdisk \-l
  89 command) at regular intervals --- at boot time, and/or every week or so.
  90 The image file should be stored on some filesystem other than
  91 the filesystem whose data it contains, to ensure that this data is
  92 accessible in the case where the filesystem has been badly damaged.
  93 .PP
  94 To save disk space,
  95 .B e2image
  96 creates the image file as a sparse file, or in QCOW2 format.
  97 Hence, if the sparse image file
  98 needs to be copied to another location, it should
  99 either be compressed first or copied using the
 100 .B \-\-sparse=always
 101 option to the GNU version of
 102 .BR cp .
 103 This does not apply to the QCOW2 image, which is not sparse.
 104 .PP
 105 The size of an ext2 image file depends primarily on the size of the
 106 filesystems and how many inodes are in use.  For a typical 10 gigabyte
 107 filesystem, with 200,000 inodes in use out of 1.2 million inodes, the
 108 image file will be approximately 35 megabytes; a 4 gigabyte filesystem with
 109 15,000 inodes in use out of 550,000 inodes will result in a 3 megabyte
 110 image file.  Image files tend to be quite
 111 compressible; an image file taking up 32 megabytes of space on
 112 disk will generally compress down to 3 or 4 megabytes.
 113 .PP
 114 .SH RESTORING FILESYSTEM METADATA USING AN IMAGE FILE
 115 .PP
 116 The
 117 .B \-I
 118 option will cause e2image to install the metadata stored in the image
 119 file back to the device.  It can be used to restore the filesystem metadata
 120 back to the device in emergency situations.
 121 .PP
 122 .B WARNING!!!!
 123 The
 124 .B \-I
 125 option should only be used as a desperation measure when other
 126 alternatives have failed.  If the filesystem has changed since the image
 127 file was created, data
 128 .B will
 129 be lost.  In general, you should make a full image
 130 backup of the filesystem first, in case you wish to try other recovery
 131 strategies afterwards.
 132 .PP
 133 .SH RAW IMAGE FILES
 134 The
 135 .B \-r
 136 option will create a raw image file instead of a normal image file.
 137 A raw image file differs
 138 from a normal image file in two ways.  First, the filesystem metadata is
 139 placed in the proper position so that e2fsck, dumpe2fs, debugfs,
 140 etc.\& can be run directly on the raw image file.  In order to minimize
 141 the amount of disk space consumed by a raw image file, the file is
 142 created as a sparse file.  (Beware of copying or
 143 compressing/decompressing this file with utilities that don't understand
 144 how to create sparse files; the file will become as large as the
 145 filesystem itself!)  Secondly, the raw image file also includes indirect
 146 blocks and directory blocks, which the standard image file does not have,
 147 although this may change in the future.
 148 .PP
 149 Raw image files are sometimes used when sending filesystems to the maintainer
 150 as part of bug reports to e2fsprogs.  When used in this capacity, the
 151 recommended command is as follows (replace hda1 with the appropriate device):
 152 .PP
 153 .br
 154         \fBe2image \-r /dev/hda1 \- | bzip2 > hda1.e2i.bz2\fR
 155 .PP
 156 This will only send the metadata information, without any data blocks.
 157 However, the filenames in the directory blocks can still reveal
 158 information about the contents of the filesystem that the bug reporter
 159 may wish to keep confidential.  To address this concern, the
 160 .B \-s
 161 option can be specified.  This will cause
 162 .B e2image
 163 to scramble directory entries and zero out any unused portions
 164 of the directory blocks before writing the image file.  However,
 165 the
 166 .B \-s
 167 option will prevent analysis of problems related to hash-tree indexed
 168 directories.
 169 .PP
 170 Note that this will work even if you substitute "/dev/hda1" for another raw
 171 disk image, or QCOW2 image previously created by
 172 .BR e2image .
 173 .PP
 174 .SH QCOW2 IMAGE FILES
 175 The
 176 .B \-Q
 177 option will create a QCOW2 image file instead of a normal, or raw image file.
 178 A QCOW2 image contains all the information the raw image does, however unlike
 179 the raw image it is not sparse. The QCOW2 image minimize the amount of disk
 180 space by storing data in special format with pack data closely together, hence
 181 avoiding holes while still minimizing size.
 182 .PP
 183 In order to send filesystem to the maintainer as a part of bug report to
 184 e2fsprogs, use following commands (replace hda1 with the appropriate device):
 185 .PP
 186 .br
 187 \       \fBe2image \-Q /dev/hda1 hda1.qcow2\fR
 188 .br
 189 \       \fBbzip2 -z hda1.qcow2\fR
 190 .PP
 191 This will only send the metadata information, without any data blocks.
 192 However, the filenames in the directory blocks can still reveal
 193 information about the contents of the filesystem that the bug reporter
 194 may wish to keep confidential.  To address this concern, the
 195 .B \-s
 196 option can be specified.  This will cause
 197 .B e2image
 198 to scramble directory entries and zero out any unused portions
 199 of the directory blocks before writing the image file.  However, the
 200 .B \-s
 201 option will prevent analysis of problems related to hash-tree indexed
 202 directories.
 203 .PP
 204 Note that QCOW2 image created by
 205 .B e2image
 206 is regular QCOW2 image and can be processed by tools aware of QCOW2 format
 207 such as for example
 208 .BR qemu-img .
 209 .PP
 210 You can convert a qcow2 image into a raw image with:
 211 .PP
 212 .br
 213 \       \fBe2image \-r hda1.qcow2 hda1.raw\fR
 214 .br
 215 .PP
 216 This can be useful to write a qcow2 image containing all data to a
 217 sparse image file where it can be loop mounted, or to a disk partition.
 218 Note that this may not work with qcow2 images not generated by e2image.
 219 .PP
 220 .SH INCLUDING DATA
 221 Normally
 222 .B e2image
 223 only includes fs metadata, not regular file data.  The
 224 .B \-a
 225 option can be specified to include all data.  This will
 226 give an image that is suitable to use to clone the entire FS or
 227 for backup purposes.  Note that this option only works with the
 228 raw or QCOW2 formats.  The
 229 .B \-p
 230 switch may be given to show progress.  If the file system is being
 231 cloned to a flash-based storage device (where reads are very fast and
 232 where it is desirable to avoid unnecessary writes to reduce write wear
 233 on the device), the
 234 .B \-c
 235 option which cause e2image to try reading a block from the destination
 236 to see if it is identical to the block which
 237 .B e2image
 238 is about to copy.  If the block is already the same, the write can be
 239 skipped.  The
 240 .B \-n
 241 option will cause all of the writes to be no-ops, and print the blocks
 242 that would have been written.
 243 .PP
 244 .SH OFFSETS
 245 Normally a filesystem starts at the beginning of a partition, and
 246 .B e2image
 247 is run on the partition.  When working with image files, you don't
 248 have the option of using the partition device, so you can specify
 249 the offset where the filesystem starts directly with the
 250 .B \-o
 251 option.  Similarly the
 252 .B \-O
 253 option specifies the offset that should be seeked to in the destination
 254 before writing the filesystem.
 255 .PP
 256 For example, if you have a
 257 .B dd
 258 image of a whole hard drive that contains an ext2 fs in a partition
 259 starting at 1 MiB, you can clone that fs with:
 260 .PP
 261 .br
 262 \       \fBe2image \-aro 1048576 img /dev/sda1\fR
 263 .br
 264 .PP
 265 Or you can clone a fs into an image file, leaving room in the first
 266 MiB for a partition table with:
 267 .PP
 268 .br
 269 \       \fBe2image -arO 1048576 /dev/sda1 img\fR
 270 .br
 271 .PP
 272 If you specify at least one offset, and only one file, an in-place
 273 move will be performed, allowing you to safely move the filesystem
 274 from one offset to another.
 275 .SH AUTHOR
 276 .B e2image
 277 was written by Theodore Ts'o (tytso@mit.edu).
 278 .SH AVAILABILITY
 279 .B e2image
 280 is part of the e2fsprogs package and is available from
 281 http://e2fsprogs.sourceforge.net.
 282 .SH SEE ALSO
 283 .BR dumpe2fs (8),
 284 .BR debugfs (8)
 285