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120 lines
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5.2 KiB
Markdown
120 lines
No EOL
5.2 KiB
Markdown
---
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date: 2023-01-18 11:08:20-05:00
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draft: false
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math: false
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medium_enabled: true
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medium_post_id: b4f33babc3ac
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tags: []
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title: 'Bmaptool: A simpler way to copy ISOs'
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---
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Bmaptool is a project created by Intel for creating and copying data using block maps. It's meant to be a simpler, faster, and more reliable tool than `dd`.
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From their [GitHub page](https://github.com/intel/bmap-tools):
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> - Faster. Depending on various factors, like write speed, image size, how full is the image, and so on, `bmaptool` was 5-7 times faster than `dd` in the Tizen IVI project.
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> - Integrity. `bmaptool` verifies data integrity while flashing, which means that possible data corruptions will be noticed immediately.
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> - Usability. `bmaptool` can read images directly from the remote server, so users do not have to download images and save them locally.
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> - Protects user's data. Unlike `dd`, if you make a mistake and specify a wrong block device name, `bmaptool` will less likely destroy your data because it has protection mechanisms which, for example, prevent `bmaptool` from writing to a mounted block device.
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It comes with two commands **create** and **copy**. Create generates the block maps which isn't required to use the application. However, having a bmap will speed up the copying process. The syntax of the copy command is the following
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```bash
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sudo bmaptool copy SRC DST
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```
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Let's say that I want to flash the latest Ubuntu ISO to a USB stick located at `/dev/sdX`. As the third bullet point claims, I can easily use the URL as SRC and since we don't have a bmap, we'll have to specify that with the flag `--nobmap`.
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```bash
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sudo bmaptool copy --nobmap https://releases.ubuntu.com/22.04.1/ubuntu-22.04.1-desktop-amd64.iso /dev/sdX
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```
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Example run on my desktop:
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```
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bmaptool: info: no bmap given, copy entire image to '/dev/sdX'
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/
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bmaptool: info: synchronizing '/dev/sdX'
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bmaptool: info: copying time: 3m 7.3s, copying speed 19.5 MiB/sec
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```
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Now if we have the ISO downloaded on our computer, we can take the time to create a bmap for it.
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```bash
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sudo bmaptool create ubuntu-22.04.1-desktop-amd64.iso > ubuntu-22.04.1-desktop-amd64.bmap
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```
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A bmap file is a human readable XML file that shows the block map and the checksums for each block.
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```xml
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<?xml version="1.0" ?>
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<!-- This file contains the block map for an image file, which is basically
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a list of useful (mapped) block numbers in the image file. In other words,
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it lists only those blocks which contain data (boot sector, partition
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table, file-system metadata, files, directories, extents, etc). These
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blocks have to be copied to the target device. The other blocks do not
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contain any useful data and do not have to be copied to the target
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device.
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The block map an optimization which allows to copy or flash the image to
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the image quicker than copying of flashing the entire image. This is
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because with bmap less data is copied: <MappedBlocksCount> blocks instead
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of <BlocksCount> blocks.
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Besides the machine-readable data, this file contains useful commentaries
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which contain human-readable information like image size, percentage of
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mapped data, etc.
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The 'version' attribute is the block map file format version in the
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'major.minor' format. The version major number is increased whenever an
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incompatible block map format change is made. The minor number changes
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in case of minor backward-compatible changes. -->
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<bmap version="2.0">
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<!-- Image size in bytes: 3.6 GiB -->
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<ImageSize> 3826831360 </ImageSize>
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<!-- Size of a block in bytes -->
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<BlockSize> 4096 </BlockSize>
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<!-- Count of blocks in the image file -->
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<BlocksCount> 934285 </BlocksCount>
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<!-- Count of mapped blocks: 3.6 GiB or 100.0% -->
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<MappedBlocksCount> 934285 </MappedBlocksCount>
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<!-- Type of checksum used in this file -->
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<ChecksumType> sha256 </ChecksumType>
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<!-- The checksum of this bmap file. When it is calculated, the value of
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the checksum has be zero (all ASCII "0" symbols). -->
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<BmapFileChecksum> e69f56b4cf11a26fba8700bc66a443a20f667d0d0fe1c2d8028715ac060c402d </BmapFileChecksum>
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<!-- The block map which consists of elements which may either be a
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range of blocks or a single block. The 'chksum' attribute
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(if present) is the checksum of this blocks range. -->
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<BlockMap>
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<Range chksum="c396e956a9f52c418397867d1ea5c0cf1a99a49dcf648b086d2fb762330cc88d"> 0-934284 </Range>
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</BlockMap>
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</bmap>
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```
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Once we have generated the bmap, we can copy the ISO to the device.
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```bash
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sudo bmaptool copy ubuntu-22.04.1-desktop-amd64.iso /dev/sdX
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```
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Example run on my desktop:
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```
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bmaptool: info: discovered bmap file 'ubuntu-22.04.1-desktop-amd64.bmap'
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bmaptool: info: block map format version 2.0
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bmaptool: info: 934285 blocks of size 4096 (3.6 GiB), mapped 934285 blocks (3.6 GiB or 100.0%)
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bmaptool: info: copying image 'ubuntu-22.04.1-desktop-amd64.iso' to block device '/dev/sdX' using bmap file 'ubuntu-22.04.1-desktop-amd64.bmap'
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bmaptool: info: 100% copied
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bmaptool: info: synchronizing '/dev/sdX'
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bmaptool: info: copying time: 2m 49.2s, copying speed 21.6 MiB/sec
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```
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Recall that the `bmap` generation isn't necessary, as you can pass in the `--nobmap` flag. |