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96 lines
2.9 KiB
Markdown
96 lines
2.9 KiB
Markdown
# dd
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Convert and copy a file.
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## TL;DR
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N and BYTES values may be followed by the following multiplicative suffixes:
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| suffix | multiplication |
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| ----------- | ------------------- |
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| `c` | 1 |
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| `w` | 2 |
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| `b` | 512 |
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| `kB` | 1000 |
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| `K` | 1024 |
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| `MB` | 1000 * 1000 |
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| `M` or `xM` | 1024 * 1024 |
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| `GB` | 1000 \* 1000 * 1000 |
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| `G` | 1024 \* 1024 * 1024 |
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and so on for T, P, E, Z, Y.
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```sh
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# Read 512 random Bytes for each iteration and save them.
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dd if='/dev/urandom' of='output/file' count=2 bs=512
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# Read 1000 Bytes for each iteration and save them while watching the progress.
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dd if='/input/file' of='output/file' count=4M bs=1k status='progress'
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# Create a 1GiB file with nothing but zeros, ready to mkswap(8) it.
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dd if='/dev/zero' of='/swapfile' count=1048576 bs=1024
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# Make a bootable USB drive from an isohybrid file.
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dd if=file.iso of=/dev/usb_drive status=progress
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# Clone a drive to another drive with 4 MiB block.
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# Ignore any error and show the progress.
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dd if=/dev/source_drive of=/dev/dest_drive bs=4M conv=noerror status=progress
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# Generate a system backup into an IMG file and show the progress:
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dd if=/dev/drive_device of=path/to/file.img status=progress
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# Restore a drive from an IMG file and show the progress:
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dd if=path/to/file.img of=/dev/drive_device status=progress
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# Create images from disks.
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sudo dd if=/dev/mmcblk0 of=/tmp/mmcblk0.img conv=sync bs=4k
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sudo dd if=/dev/sda conv=sync,noerror bs=64K | gzip -c > /mnt/sdb/disk.img.gz
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# Write an image to disk.
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sudo dd if=/tmp/mmcblk0.img of=/dev/mmcblk0 conv=fsync oflag=direct bs=4M status=progress
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# Clone a disk on another disk.
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sudo dd if=/dev/sda of=/dev/sdb conv=fsync bs=4M oflag=direct status=progress
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```
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## Benchmark disks
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Use:
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- a single, bigger file for throughput (write speed)
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- multiple, smaller files for latency
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```sh
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dd \
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if=/dev/input.file of=/path/to/output.file \
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bs=block-size count=number-of-blocks \
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oflag=dsync status=progress
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```
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Examples:
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```sh
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dd if=/dev/zero of=/tmp/test1.img bs=1G count=1 oflag=dsync
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dd if=/dev/zero of=/tmp/test2.img bs=64M count=1 oflag=dsync
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dd if=/dev/zero of=/tmp/test3.img bs=1M count=256 conv=fdatasync
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dd if=/dev/zero of=/tmp/test4.img bs=8k count=10k
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dd if=/dev/zero of=/tmp/test4.img bs=512 count=1000 oflag=dsync
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```
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## Further readings
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## Sources
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All the references in the [further readings] section, plus the following:
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- [cheat.sh]
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- [Linux and Unix Test Disk I/O Performance With dd Command]
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<!-- upstream -->
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<!-- internal references -->
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<!-- external references -->
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[cheat.sh]: https://cheat.sh/dd
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[how to create a disk image in linux]: https://itstillworks.com/clone-hard-drive-ubuntu-6884403.html
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[linux and unix test disk i/o performance with dd command]: https://www.cyberciti.biz/faq/howto-linux-unix-test-disk-performance-with-dd-command/
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