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 filesystem metadata to a file
   8 .SH SYNOPSIS
   9 .B e2image
  10 [
  11 .B \-rsI
  12 ]
  13 .I device
  14 .I image-file
  15 .SH DESCRIPTION
  16 The
  17 .B e2image
  18 program will save critical ext2 or ext3 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 currently
  44 requires random access to the file, which cannot be done using a
  45 pipe.  This restriction will hopefully be lifted in a future version of
  46 .BR e2image .)
  47 .PP
  48 It is a very good idea to create image files for all of
  49 filesystems on a system and save the partition
  50 layout (which can be generated using the
  51 .B fdisk \-l
  52 command) at regular intervals --- at boot time, and/or every week or so.
  53 The image file should be stored on some filesystem
  54 other that
  55 the filesystem whose data it contains, to ensure that its 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.
  61 Hence, if the 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 .PP
  68 The size of an ext2 image file depends primarily on the size of the
  69 filesystems and how many inodes are in use.  For a typical 10 gigabyte
  70 filesystem, with 200,000 inodes in use out of 1.2 million inodes, the
  71 image file will be approximately 35 megabytes; a 4 gigabyte filesystem with
  72 15,000 inodes in use out of 550,000 inodes will result in a 3 megabyte
  73 image file.  Image files tend to be quite
  74 compressible; an image file taking up 32 megabytes of space on
  75 disk will generally compress down to 3 or 4 megabytes.
  76 .PP
  77 .SH RESTORING FILESYSTEM METADATA USING AN IMAGE FILE
  78 .PP
  79 The
  80 .B \-I
  81 option will cause e2image to install the metadata stored in the image
  82 file back to the device.    It can be used to restore the filesystem metadata
  83 back to the device in emergency situations.
  84 .PP
  85 .B WARNING!!!!
  86 The
  87 .B \-I
  88 option should only be used as a desperation measure when other
  89 alternatives have failed.  If the filesystem has changed since the image
  90 file was created, data
  91 .B will
  92 be lost.  In general, you should make a full image
  93 backup of the filesystem first, in case you wish to try other recovery
  94 strategies afterwards.
  95 .PP
  96 .SH RAW IMAGE FILES
  97 The
  98 .B \-r
  99 option will create a raw image file instead of a normal image file.
 100 A raw image file differs
 101 from a normal image file in two ways.  First, the filesystem metadata is
 102 placed in the proper position so that e2fsck, dumpe2fs, debugfs,
 103 etc. can be run directly on the raw image file.  In order to minimize
 104 the amount of disk space consumed by a raw image file, the file is
 105 created as a sparse file.  (Beware of copying or
 106 compressing/decompressing this file with utilities that don't understand
 107 how to create sparse files; the file will become as large as the
 108 filesystem itself!)  Secondly, the raw image file also includes indirect
 109 blocks and directory blocks, which the standard image file does not have,
 110 although this may change in the future.
 111 .PP
 112 Raw image files are sometimes used when sending filesystems to the maintainer
 113 as part of bug reports to e2fsprogs.  When used in this capacity, the
 114 recommended command is as follows (replace hda1 with the appropriate device):
 115 .PP
 116 .br
 117 \       \fBe2image \-r /dev/hda1 \- | bzip2 > hda1.e2i.bz2\fR
 118 .PP
 119 This will only send the metadata information, without any data blocks.
 120 However, the filenames in the directory blocks can still reveal
 121 information about the contents of the filesystem that the bug reporter
 122 may wish to keep confidential.  To address this concern, the
 123 .B \-s
 124 option can be specified.  This will cause
 125 .B e2image
 126 to scramble directory entries and zero out any unused portions
 127 of the directory blocks before writing the image file.  However,
 128 the
 129 .B \-s
 130 option will prevent analysis of problems related to hash-tree indexed
 131 directories.
 132 .PP
 133 .SH AUTHOR
 134 .B e2image
 135 was written by Theodore Ts'o (tytso@mit.edu).
 136 .SH AVAILABILITY
 137 .B e2image
 138 is part of the e2fsprogs package and is available from
 139 http://e2fsprogs.sourceforge.net.
 140 .SH SEE ALSO
 141 .BR dumpe2fs (8),
 142 .BR debugfs (8)
 143