diff options
Diffstat (limited to 'misc/e2image.8.in')
| -rw-r--r-- | misc/e2image.8.in | 335 |
1 files changed, 335 insertions, 0 deletions
diff --git a/misc/e2image.8.in b/misc/e2image.8.in new file mode 100644 index 0000000..90ea0c2 --- /dev/null +++ b/misc/e2image.8.in @@ -0,0 +1,335 @@ +.\" -*- nroff -*- +.\" Copyright 2001 by Theodore Ts'o. All Rights Reserved. +.\" This file may be copied under the terms of the GNU Public License. +.\" +.TH E2IMAGE 8 "@E2FSPROGS_MONTH@ @E2FSPROGS_YEAR@" "E2fsprogs version @E2FSPROGS_VERSION@" +.SH NAME +e2image \- Save critical ext2/ext3/ext4 file system metadata to a file + +.SH SYNOPSIS +.B e2image +.RB [ \-r | \-Q " [" \-af ]] +[ +.B \-b +.I superblock +] +[ +.B \-B +.I blocksize +] +[ +.B \-cnps +] +[ +.B \-o +.I src_offset +] +[ +.B \-O +.I dest_offset +] +.I device +.I image-file +.br +.B e2image +.B \-I +.I device +.I image-file + +.SH DESCRIPTION +The +.B e2image +program will save critical ext2, ext3, or ext4 file system metadata located on +.I device +to a file specified by +.IR image-file . +The image file may be examined by +.B dumpe2fs +and +.BR debugfs , +by using the +.B \-i +option to those programs. This can assist an expert in recovering +catastrophically corrupted file systems. +.PP +It is a very good idea to create image files for all file systems on a +system and save the partition layout (which can be generated using the +.B fdisk \-l +command) at regular intervals --- at boot time, and/or every week or so. +The image file should be stored on some file system other than +the file system whose data it contains, to ensure that this data is +accessible in the case where the file system has been badly damaged. +.PP +To save disk space, +.B e2image +creates the image file as a sparse file, or in QCOW2 format. Hence, if +the sparse image file needs to be copied to another location, it should +either be compressed first or copied using the +.B \-\-sparse=always +option to the GNU version of +.BR cp (1). +This does not apply to the QCOW2 image, which is not sparse. +.PP +The size of an ext2 image file depends primarily on the size of the +file systems and how many inodes are in use. For a typical 10 Gigabyte +file system, with 200,000 inodes in use out of 1.2 million inodes, the image +file will be approximately 35 Megabytes; a 4 Gigabyte file system with 15,000 +inodes in use out of 550,000 inodes will result in a 3 Megabyte image file. +Image files tend to be quite compressible; an image file taking up 32 Megabytes +of space on disk will generally compress down to 3 or 4 Megabytes. +.PP +If +.I image-file +is +.BR \- , +then the output of +.B e2image +will be sent to standard output, so that the output can be piped to +another program, such as +.BR gzip (1). +(Note that this is currently only supported when +creating a raw image file using the +.B \-r +option, since the process of creating a normal image file, or QCOW2 +image currently +requires random access to the file, which cannot be done using a +pipe. + +.SH OPTIONS +.TP +.B \-a +Include file data in the image file. Normally +.B e2image +only includes fs metadata, not regular file data. This option will +produce an image that is suitable to use to clone the entire FS or +for backup purposes. Note that this option only works with the +raw +.RI ( \-r ) +or QCOW2 +.RI ( \-Q ) +formats. In conjunction with the +.B \-r +option it is possible to clone all and only the used blocks of one +file system to another device/image file. +.TP +.BI \-b " superblock" +Get image from partition with broken primary superblock by using +the superblock located at file system block number +.IR superblock . +The partition is copied as-is including broken primary superblock. +.TP +.BI \-B " blocksize" +Set the file system blocksize in bytes. Normally, +.B e2image +will search for the superblock at various different block sizes in an +attempt to find the appropriate blocksize. This search can be fooled in +some cases. This option forces e2fsck to only try locating the superblock +with a particular blocksize. If the superblock is not found, e2image will +terminate with a fatal error. +.TP +.BI \-c +Compare each block to be copied from the source +.I device +to the corresponding block in the target +.IR image-file . +If both are already the same, the write will be skipped. This is +useful if the file system is being cloned to a flash-based storage device +(where reads are very fast and where it is desirable to avoid unnecessary +writes to reduce write wear on the device). +.TP +.B \-f +Override the read-only requirement for the source file system when saving +the image file using the +.B \-r +and +.B \-Q +options. Normally, if the source file system is in use, the resulting image +file is very likely not going to be useful. In some cases where the source +file system is in constant use this may be better than no image at all. +.TP +.B \-I +install the metadata stored in the image file back to the device. +It can be used to restore the file system metadata back to the device +in emergency situations. +.PP +.B WARNING!!!! +The +.B \-I +option should only be used as a desperation measure when other +alternatives have failed. If the file system has changed since the image +file was created, data +.B will +be lost. In general, you should make another full image backup of the +file system first, in case you wish to try other recovery strategies afterward. +.TP +.B \-n +Cause all image writes to be skipped, and instead only print the block +numbers that would have been written. +.TP +.BI \-o " src_offset" +Specify offset of the image to be read from the start of the source +.I device +in bytes. See +.B OFFSETS +for more details. +.TP +.BI \-O " tgt_offset" +Specify offset of the image to be written from the start of the target +.I image-file +in bytes. See +.B OFFSETS +for more details. +.TP +.B \-p +Show progress of image-file creation. +.TP +.B \-Q +Create a QCOW2-format image file instead of a normal image file, suitable +for use by virtual machine images, and other tools that can use the +.B .qcow +image format. See +.B QCOW2 IMAGE FILES +below for details. +.TP +.B \-r +Create a raw image file instead of a normal image file. See +.B RAW IMAGE FILES +below for details. +.TP +.B \-s +Scramble directory entries and zero out unused portions of the directory +blocks in the written image file to avoid revealing information about +the contents of the file system. However, this will prevent analysis of +problems related to hash-tree indexed directories. + +.SH RAW IMAGE FILES +The +.B \-r +option will create a raw image file, which differs +from a normal image file in two ways. First, the file system metadata is +placed in the same relative offset within +.I image-file +as it is in the +.I device +so that +.BR debugfs (8), +.BR dumpe2fs (8), +.BR e2fsck (8), +.BR losetup (8), +etc. and can be run directly on the raw image file. In order to minimize +the amount of disk space consumed by the raw image file, it is +created as a sparse file. (Beware of copying or +compressing/decompressing this file with utilities that don't understand +how to create sparse files; the file will become as large as the +file system itself!) Secondly, the raw image file also includes indirect +blocks and directory blocks, which the standard image file does not have. +.PP +Raw image files are sometimes used when sending file systems to the maintainer +as part of bug reports to e2fsprogs. When used in this capacity, the +recommended command is as follows (replace +.B hda1 +with the appropriate device for your system): +.PP +.br + \fBe2image \-r /dev/hda1 \- | bzip2 > hda1.e2i.bz2\fR +.PP +This will only send the metadata information, without any data blocks. +However, the filenames in the directory blocks can still reveal +information about the contents of the file system that the bug reporter +may wish to keep confidential. To address this concern, the +.B \-s +option can be specified to scramble the filenames in the image. +.PP +Note that this will work even if you substitute +.B /dev/hda1 +for another raw +disk image, or QCOW2 image previously created by +.BR e2image . + +.SH QCOW2 IMAGE FILES +The +.B \-Q +option will create a QCOW2 image file instead of a normal, or raw image file. +A QCOW2 image contains all the information the raw image does, however unlike +the raw image it is not sparse. The QCOW2 image minimize the amount of space +used by the image by storing it in special format which packs data closely +together, hence avoiding holes while still minimizing size. +.PP +In order to send file system to the maintainer as a part of bug report to +e2fsprogs, use following commands (replace +.B hda1 +with the appropriate device for your system): +.PP +.br +\ \fBe2image \-Q /dev/hda1 hda1.qcow2\fR +.br +\ \fBbzip2 -z hda1.qcow2\fR +.PP +This will only send the metadata information, without any data blocks. +As described for +.B RAW IMAGE FILES +the +.B \-s +option can be specified to scramble the file system names in the image. +.PP +Note that the QCOW2 image created by +.B e2image +is a regular QCOW2 image and can be processed by tools aware of QCOW2 format +such as for example +.BR qemu-img . +.PP +You can convert a .qcow2 image into a raw image with: +.PP +.br +\ \fBe2image \-r hda1.qcow2 hda1.raw\fR +.br +.PP +This can be useful to write a QCOW2 image containing all data to a +sparse image file where it can be loop mounted, or to a disk partition. +Note that this may not work with QCOW2 images not generated by e2image. + +.SH OFFSETS +Normally a file system starts at the beginning of a partition, and +.B e2image +is run on the partition. When working with image files, you don't +have the option of using the partition device, so you can specify +the offset where the file system starts directly with the +.B \-o +option. Similarly the +.B \-O +option specifies the offset that should be seeked to in the destination +before writing the file system. +.PP +For example, if you have a +.B dd +image of a whole hard drive that contains an ext2 fs in a partition +starting at 1 MiB, you can clone that image to a block device with: +.PP +.br +\ \fBe2image \-aro 1048576 img /dev/sda1\fR +.br +.PP +Or you can clone a file system from a block device into an image file, +leaving room in the first MiB for a partition table with: +.PP +.br +\ \fBe2image -arO 1048576 /dev/sda1 img\fR +.br +.PP +If you specify at least one offset, and only one file, an in-place +move will be performed, allowing you to safely move the file system +from one offset to another. + +.SH AUTHOR +.B e2image +was written by Theodore Ts'o (tytso@mit.edu). + +.SH AVAILABILITY +.B e2image +is part of the e2fsprogs package and is available from +http://e2fsprogs.sourceforge.net. + +.SH SEE ALSO +.BR dumpe2fs (8), +.BR debugfs (8) +.BR e2fsck (8) |