CheatPress

dd Raw block copier

Version 9.7 · source

dd, Postcard, light preview Light · Postcard 102 × 152 mm · PDF dd, Postcard, dark preview Dark · Postcard 102 × 152 mm · PDF dd, Postcard, ink saver preview Ink saver · Postcard 102 × 152 mm · PDF
dd, A5, light preview Light · A5 148 × 210 mm · PDF dd, A5, dark preview Dark · A5 148 × 210 mm · PDF dd, A5, ink saver preview Ink saver · A5 148 × 210 mm · PDF
dd, A4, light preview Light · A4 210 × 297 mm · PDF dd, A4, dark preview Dark · A4 210 × 297 mm · PDF dd, A4, ink saver preview Ink saver · A4 210 × 297 mm · PDF
dd, A4 landscape, light preview Light · A4 landscape 297 × 210 mm · PDF dd, A4 landscape, dark preview Dark · A4 landscape 297 × 210 mm · PDF dd, A4 landscape, ink saver preview Ink saver · A4 landscape 297 × 210 mm · PDF
dd, A3, light preview Light · A3 297 × 420 mm · PDF dd, A3, dark preview Dark · A3 297 × 420 mm · PDF dd, A3, ink saver preview Ink saver · A3 297 × 420 mm · PDF
dd, A3 landscape, light preview Light · A3 landscape 420 × 297 mm · PDF dd, A3 landscape, dark preview Dark · A3 landscape 420 × 297 mm · PDF dd, A3 landscape, ink saver preview Ink saver · A3 landscape 420 × 297 mm · PDF
dd, Letter, light preview Light · Letter 8.5 × 11 in · PDF dd, Letter, dark preview Dark · Letter 8.5 × 11 in · PDF dd, Letter, ink saver preview Ink saver · Letter 8.5 × 11 in · PDF
dd, Tabloid, light preview Light · Tabloid 11 × 17 in · PDF dd, Tabloid, dark preview Dark · Tabloid 11 × 17 in · PDF dd, Tabloid, ink saver preview Ink saver · Tabloid 11 × 17 in · PDF

Start here

lsblk
Find the right device
dd if=<in> of=<out> bs=4M status=progress
Copy with progress
dd if=<iso> of=/dev/<usb> bs=4M conv=fsync
Write an image to USB
dd if=/dev/<disk> of=<img> bs=1M
Disk to image file
dd if=/dev/zero of=<file> bs=1M count=100
Make a 100 MiB file
dd if=<in> of=<out> count=1
Copy one block only
kill -USR1 $(pidof dd)
Show progress now
sync
Flush writes to disk

Concepts

  1. if= input file or device
  2. dd conv= converts
  3. of= output file or device

Basics

dd if=<in> of=<out>
Copy a file or device
bs=<size>
Block size for read and write
count=<n>
Copy only n input blocks
skip=<n>
Skip n blocks of input first
seek=<n>
Skip n blocks of output first
status=progress
Show running transfer stats
status=none
Print only errors
status=noxfer
Hide the final summary
bs=4M
Good default for disks and USB
ibs=<size> obs=<size>
Separate read and write sizes
count=<n>B
Count bytes instead of blocks
skip=<n>B
Skip bytes instead of blocks
kill -USR1 $(pidof dd)
Print stats once, keep copying
watch -n1 kill -USR1 $(pidof dd)
Poll stats on a dd already running

Writing and flushing

conv=fsync
Flush data and metadata at the end
conv=fdatasync
Flush data only at the end
oflag=sync
Synchronous writes, slow and safe
oflag=direct
Bypass the page cache on write
iflag=direct
Bypass the page cache on read
conv=notrunc
Do not truncate the output file
conv=excl
Fail if the output exists
conv=nocreat
Fail if the output is missing
oflag=append conv=notrunc
Append to the output
iflag=fullblock
Fill whole blocks when reading pipes
iflag=nocache oflag=nocache
Drop cached pages after use

Conversions and errors

conv=noerror,sync
Continue on read errors, pad with zeros
conv=sparse
Skip all-zero blocks, make a sparse file
conv=swab
Swap every pair of bytes
conv=ucase
Upper-case the text
conv=lcase
Lower-case the text
conv=ascii
EBCDIC to ASCII
conv=ebcdic
ASCII to EBCDIC
conv=block cbs=<n>
Pad lines to fixed-width records
conv=unblock cbs=<n>
Trim fixed-width records to lines
iflag=skip_bytes
Read skip= as a byte count

Disks and images

lsblk -o NAME,SIZE,MODEL,TRAN,MOUNTPOINT
Identify the target device
dd if=<iso> of=/dev/<usb> bs=4M conv=fsync status=progress
Write an ISO to a USB stick
dd if=/dev/<disk> of=<disk.img> bs=4M status=progress
Back up a whole disk
dd if=<disk.img> of=/dev/<disk> bs=4M conv=fsync
Restore a disk image
dd if=/dev/<disk> bs=4M | gzip > <disk.img.gz>
Compressed disk image
gunzip -c <disk.img.gz> | dd of=/dev/<disk> bs=4M
Restore compressed image
dd if=/dev/<disk> of=<mbr.bin> bs=512 count=1
Save the first sector (MBR)
dd if=<mbr.bin> of=/dev/<disk> bs=446 count=1
Restore boot code, keep partitions
dd if=/dev/<part> of=<part.img> bs=4M
Image a single partition
dd if=/dev/<disk> bs=4M | ssh <host> 'dd of=<disk.img>'
Image a disk over SSH
dd if=<in> bs=4M | pv | dd of=<out> bs=4M
Progress bar through pv
dd if=<disk.img> bs=4M | sha256sum
Hash the image to verify
cmp <iso> /dev/<usb> -n $(stat -c %s <iso>)
Verify what was written
blockdev --getsize64 /dev/<disk>
Device size in bytes

Wiping and test files

dd if=/dev/zero of=<file> bs=1M count=<n>
File of n MiB zeros
dd if=/dev/zero of=<file> bs=1 count=0 seek=<size>
Sparse file, no data written
dd if=/dev/urandom of=<file> bs=1M count=<n>
File of random bytes
dd if=/dev/zero of=/dev/<disk> bs=4M status=progress
Zero a whole disk
dd if=/dev/urandom of=/dev/<disk> bs=4M status=progress
Overwrite with random data
dd if=/dev/zero of=/dev/<disk> bs=1M count=10
Wipe start of disk (old signatures)
dd if=/dev/zero of=/dev/<disk> bs=1M seek=$(( <MiB> - 10 ))
Wipe the end of the disk
truncate -s <size> <file>
Resize or create a sparse file

Benchmarking and extraction

dd if=/dev/zero of=<file> bs=1G count=1 oflag=direct
Rough write speed
dd if=<file> of=/dev/null bs=1M
Rough read speed
echo 3 | sudo tee /proc/sys/vm/drop_caches
Drop caches before a read test
dd if=<file> of=/dev/null bs=1M iflag=direct
Read speed without the cache
dd if=<in> of=<out> bs=1 skip=<off> count=<len>
Cut a byte range from a file
dd if=<in> of=<out> bs=<n> skip=1
Drop the first n bytes
dd if=<in> of=<out> bs=1 seek=<off> conv=notrunc
Patch bytes at an offset

Recipes

Make a bootable USB stick
lsblk -o NAME,SIZE,MODEL,TRANsudo umount /dev/sdX*sudo dd if=distro.iso of=/dev/sdX bs=4M conv=fsync status=progresssync
Back up and verify a disk
sudo dd if=/dev/sdX bs=4M status=progress | gzip > disk.img.gz# restore latergunzip -c disk.img.gz | sudo dd of=/dev/sdY bs=4M conv=fsync
Clone a failing disk as far as possible
sudo dd if=/dev/sdX of=rescue.img bs=64K conv=noerror,sync status=progress# smaller bs loses less per bad block
Back up and restore the MBR
sudo dd if=/dev/sdX of=mbr.bin bs=512 count=1sudo dd if=mbr.bin of=/dev/sdX bs=512 count=1