Dd (command)

dd is a command-line utility for Linux and Unix-like operating systems used to copy or create files on block devices (HDD).

Warning: write operations will not ask for confirmation if you are overwriting an existing file.

Options:

oflag=sync

iflag=[fullblock|nocache]

Examples

• Write a 10G file with random data: 10 G (bs=10G count=1), with random data (/dev/urandom):

dd iflag=fullblock if=/dev/urandom of=sample_output_file.txt bs=10G count=1 status=progress

 10737418240 bytes (11 GB, 10 GiB) copied, 66 s, 162 MB/s
 1+0 records in
 1+0 records out
 10737418240 bytes (11 GB, 10 GiB) copied, 66.4367 s, 162 MB/s

• Write a 10G with zeroes: 10 G (bs=10G count=1), file with "zeroes" (/dev/zero):

dd iflag=fullblock if=/dev/zero of=sample_output_file.txt bs=10G count=1 status=progress

 10737418240 bytes (11 GB, 10 GiB) copied, 66 s, 162 MB/s
 1+0 records in
 1+0 records out
 10737418240 bytes (11 GB, 10 GiB) copied, 66.4367 s, 162 MB/s

dd iflag=fullblock if=/dev/zero of=sample_output_file.txt bs=10G count=1
dd: memory exhausted by input buffer of size 10737418240 bytes (10 GiB)

• if=/dev/vda | gzip -1 | ssh your.server.com dd of=/mnt/storage/imagename.img.gz

• Clone an SD card

1) Copy content: sudo dd if=/dev/sdt of=~/sd-card-clone.img

2) Change card

3) Overwrite card with copied image: sudo dd if=~/sd-card-copy.img of=/dev/sdt

Activities

Basic

1. Write a 10GB file with random data and review your disk performance: dd iflag=fullblock if=/dev/urandom of=sample_output_file.txt
2. Read Linux I/O Performance Tests using dd: https://www.thomas-krenn.com/en/wiki/Linux_I/O_Performance_Tests_using_dd
3. /Benchmark disk performance using dd/

Advanced

1. Understand iflags, such us fullblock iflag=fullblock meaning
2. Try to interrupt/kill your command: dd iflag=fullblock if=/dev/urandom of=sample_output_file.txt bs=10G count=1 and explain outcome.

See also

• cp and rsync
• IO performance: iotop, iostat, sar -d, fio, nmon, vmstat -d, dd, nmon, stress
• pv
• Benchmarking tools
• file, File system, directory, touch, mkdir, ls, ln truncate, fallocate, split, stat, inode, File descriptor, superblock, block size (blockdev), fuser, lsof, scrub, chattr, ulimit (nofiles), cp, mv, file (command), mkfifo, chmod

http://man7.org/linux/man-pages/man1/dd.1.html

https://www.gnu.org/software/coreutils/manual/html_node/dd-invocation.html#dd-invocation

https://www.gnu.org/software/coreutils/manual/html_node/dd-invocation.html#dd-invocation

https://superuser.com/a/470957

https://askubuntu.com/questions/227924/sd-card-cloning-using-the-dd-command