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 [
  17 .B \-b
  18 .I superblock
  19 ]
  20 [
  21 .B \-B
  22 .I blocksize
  23 ]
  24 .I device
  25 .I image-file
  26 .br
  27 .B e2image
  28 .B \-I
  29 .I device
  30 .I image-file
  31 .br
  32 .B e2image
  33 .B \-ra
  34 [
  35 .B \-cfnp
  36 ]
  37 [
  38 .B \-o
  39 .I src_offset
  40 ]
  41 [
  42 .B \-O
  43 .I dest_offset
  44 ]
  45 .I src_fs
  46 [
  47 .I dest_fs
  48 ]
  49 .SH DESCRIPTION
  50 The
  51 .B e2image
  52 program will save critical ext2, ext3, or ext4 filesystem metadata located on
  53 .I device
  54 to a file specified by
  55 .IR image-file .
  56 The image file may be examined by
  57 .B dumpe2fs
  58 and
  59 .BR  debugfs ,
  60 by using the
  61 .B \-i
  62 option to those programs.  This can assist an expert in
  63 recovering catastrophically corrupted filesystems.  In the future,
  64 e2fsck will be enhanced to be able to use the image file to help
  65 recover a badly damaged filesystem.
  66 .PP
  67 When saving an e2image for debugging purposes, using either the
  68 .B \-r
  69 or
  70 .B \-Q
  71 options, the filesystem must be unmounted or be mounted read/only, in order
  72 for the image file to be in a consistent state.  This requirement can be
  73 overridden using the
  74 .B \-f
  75 option, but the resulting image file is very likely not going to be useful.
  76 .PP
  77 If
  78 .I image-file
  79 is \-, then the output of
  80 .B e2image
  81 will be sent to standard output, so that the output can be piped to
  82 another program, such as
  83 .BR gzip (1).
  84 (Note that this is currently only supported when
  85 creating a raw image file using the
  86 .B \-r
  87 option, since the process of creating a normal image file, or QCOW2
  88 image currently
  89 requires random access to the file, which cannot be done using a
  90 pipe.  This restriction will hopefully be lifted in a future version of
  91 .BR e2image .)
  92 .PP
  93 It is a very good idea to create image files for all of
  94 filesystems on a system and save the partition
  95 layout (which can be generated using the
  96 .B fdisk \-l
  97 command) at regular intervals --- at boot time, and/or every week or so.
  98 The image file should be stored on some filesystem other than
  99 the filesystem whose data it contains, to ensure that this data is
 100 accessible in the case where the filesystem has been badly damaged.
 101 .PP
 102 To save disk space,
 103 .B e2image
 104 creates the image file as a sparse file, or in QCOW2 format.
 105 Hence, if the sparse image file
 106 needs to be copied to another location, it should
 107 either be compressed first or copied using the
 108 .B \-\-sparse=always
 109 option to the GNU version of
 110 .BR cp .
 111 This does not apply to the QCOW2 image, which is not sparse.
 112 .PP
 113 The size of an ext2 image file depends primarily on the size of the
 114 filesystems and how many inodes are in use.  For a typical 10 gigabyte
 115 filesystem, with 200,000 inodes in use out of 1.2 million inodes, the
 116 image file will be approximately 35 megabytes; a 4 gigabyte filesystem with
 117 15,000 inodes in use out of 550,000 inodes will result in a 3 megabyte
 118 image file.  Image files tend to be quite
 119 compressible; an image file taking up 32 megabytes of space on
 120 disk will generally compress down to 3 or 4 megabytes.
 121 .PP
 122 .SH RESTORING FILESYSTEM METADATA USING AN IMAGE FILE
 123 .PP
 124 The
 125 .B \-I
 126 option will cause e2image to install the metadata stored in the image
 127 file back to the device.  It can be used to restore the filesystem metadata
 128 back to the device in emergency situations.
 129 .PP
 130 .B WARNING!!!!
 131 The
 132 .B \-I
 133 option should only be used as a desperation measure when other
 134 alternatives have failed.  If the filesystem has changed since the image
 135 file was created, data
 136 .B will
 137 be lost.  In general, you should make a full image
 138 backup of the filesystem first, in case you wish to try other recovery
 139 strategies afterwards.
 140 .PP
 141 .SH RAW IMAGE FILES
 142 The
 143 .B \-r
 144 option will create a raw image file instead of a normal image file.
 145 A raw image file differs
 146 from a normal image file in two ways.  First, the filesystem metadata is
 147 placed in the proper position so that e2fsck, dumpe2fs, debugfs,
 148 etc.\& can be run directly on the raw image file.  In order to minimize
 149 the amount of disk space consumed by a raw image file, the file is
 150 created as a sparse file.  (Beware of copying or
 151 compressing/decompressing this file with utilities that don't understand
 152 how to create sparse files; the file will become as large as the
 153 filesystem itself!)  Secondly, the raw image file also includes indirect
 154 blocks and directory blocks, which the standard image file does not have,
 155 although this may change in the future.
 156 .PP
 157 Raw image files are sometimes used when sending filesystems to the maintainer
 158 as part of bug reports to e2fsprogs.  When used in this capacity, the
 159 recommended command is as follows (replace hda1 with the appropriate device):
 160 .PP
 161 .br
 162         \fBe2image \-r /dev/hda1 \- | bzip2 > hda1.e2i.bz2\fR
 163 .PP
 164 This will only send the metadata information, without any data blocks.
 165 However, the filenames in the directory blocks can still reveal
 166 information about the contents of the filesystem that the bug reporter
 167 may wish to keep confidential.  To address this concern, the
 168 .B \-s
 169 option can be specified.  This will cause
 170 .B e2image
 171 to scramble directory entries and zero out any unused portions
 172 of the directory blocks before writing the image file.  However,
 173 the
 174 .B \-s
 175 option will prevent analysis of problems related to hash-tree indexed
 176 directories.
 177 .PP
 178 Option
 179 .B \-b
 180 .I superblock
 181 can be used to get image from partition with broken primary superblock.
 182 The partition is copied as-is including broken primary superblock.
 183 .PP
 184 Option
 185 .B \-B
 186 .I blocksize
 187 can be used to set superblock block size. Normally, e2fsck will search
 188 for the superblock at various different block sizes in an attempt to find
 189 the appropriate blocksize. This search can be fooled in some cases.  This
 190 option forces e2fsck to only try locating the superblock at a particular
 191 blocksize. If the superblock is not found, e2fsck will terminate with a
 192 fatal error.
 193 .PP
 194 Note that this will work even if you substitute "/dev/hda1" for another raw
 195 disk image, or QCOW2 image previously created by
 196 .BR e2image .
 197 .PP
 198 .SH QCOW2 IMAGE FILES
 199 The
 200 .B \-Q
 201 option will create a QCOW2 image file instead of a normal, or raw image file.
 202 A QCOW2 image contains all the information the raw image does, however unlike
 203 the raw image it is not sparse. The QCOW2 image minimize the amount of disk
 204 space by storing data in special format with pack data closely together, hence
 205 avoiding holes while still minimizing size.
 206 .PP
 207 In order to send filesystem to the maintainer as a part of bug report to
 208 e2fsprogs, use following commands (replace hda1 with the appropriate device):
 209 .PP
 210 .br
 211 \       \fBe2image \-Q /dev/hda1 hda1.qcow2\fR
 212 .br
 213 \       \fBbzip2 -z hda1.qcow2\fR
 214 .PP
 215 This will only send the metadata information, without any data blocks.
 216 However, the filenames in the directory blocks can still reveal
 217 information about the contents of the filesystem that the bug reporter
 218 may wish to keep confidential.  To address this concern, the
 219 .B \-s
 220 option can be specified.  This will cause
 221 .B e2image
 222 to scramble directory entries and zero out any unused portions
 223 of the directory blocks before writing the image file.  However, the
 224 .B \-s
 225 option will prevent analysis of problems related to hash-tree indexed
 226 directories.
 227 .PP
 228 Note that QCOW2 image created by
 229 .B e2image
 230 is regular QCOW2 image and can be processed by tools aware of QCOW2 format
 231 such as for example
 232 .BR qemu-img .
 233 .PP
 234 You can convert a qcow2 image into a raw image with:
 235 .PP
 236 .br
 237 \       \fBe2image \-r hda1.qcow2 hda1.raw\fR
 238 .br
 239 .PP
 240 This can be useful to write a qcow2 image containing all data to a
 241 sparse image file where it can be loop mounted, or to a disk partition.
 242 Note that this may not work with qcow2 images not generated by e2image.
 243 .PP
 244 Options
 245 .B \-b
 246 .I superblock
 247 and
 248 .B \-B
 249 .I blocksize
 250 can be used same way as for raw images.
 251 .PP
 252 .SH INCLUDING DATA
 253 Normally
 254 .B e2image
 255 only includes fs metadata, not regular file data.  The
 256 .B \-a
 257 option can be specified to include all data.  This will
 258 give an image that is suitable to use to clone the entire FS or
 259 for backup purposes.  Note that this option only works with the
 260 raw or QCOW2 formats.  The
 261 .B \-p
 262 switch may be given to show progress.  If the file system is being
 263 cloned to a flash-based storage device (where reads are very fast and
 264 where it is desirable to avoid unnecessary writes to reduce write wear
 265 on the device), the
 266 .B \-c
 267 option which cause e2image to try reading a block from the destination
 268 to see if it is identical to the block which
 269 .B e2image
 270 is about to copy.  If the block is already the same, the write can be
 271 skipped.  The
 272 .B \-n
 273 option will cause all of the writes to be no-ops, and print the blocks
 274 that would have been written.
 275 .PP
 276 .SH OFFSETS
 277 Normally a filesystem starts at the beginning of a partition, and
 278 .B e2image
 279 is run on the partition.  When working with image files, you don't
 280 have the option of using the partition device, so you can specify
 281 the offset where the filesystem starts directly with the
 282 .B \-o
 283 option.  Similarly the
 284 .B \-O
 285 option specifies the offset that should be seeked to in the destination
 286 before writing the filesystem.
 287 .PP
 288 For example, if you have a
 289 .B dd
 290 image of a whole hard drive that contains an ext2 fs in a partition
 291 starting at 1 MiB, you can clone that fs with:
 292 .PP
 293 .br
 294 \       \fBe2image \-aro 1048576 img /dev/sda1\fR
 295 .br
 296 .PP
 297 Or you can clone a fs into an image file, leaving room in the first
 298 MiB for a partition table with:
 299 .PP
 300 .br
 301 \       \fBe2image -arO 1048576 /dev/sda1 img\fR
 302 .br
 303 .PP
 304 If you specify at least one offset, and only one file, an in-place
 305 move will be performed, allowing you to safely move the filesystem
 306 from one offset to another.
 307 .SH AUTHOR
 308 .B e2image
 309 was written by Theodore Ts'o (tytso@mit.edu).
 310 .SH AVAILABILITY
 311 .B e2image
 312 is part of the e2fsprogs package and is available from
 313 http://e2fsprogs.sourceforge.net.
 314 .SH SEE ALSO
 315 .BR dumpe2fs (8),
 316 .BR debugfs (8)
 317