Dd (command)

dd is a command-line utility for 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)

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
• fio and iotop
• pv
• Benchmarking tools
• fallocate

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