Dd (command)
dd[1][2] 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[3]iflag=[fullblock|nocache]
Examples
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
Activities
Basic
- Write a 10GB file with random data and review your disk performance:
dd iflag=fullblock if=/dev/urandom of=sample_output_file.txt - Read Linux I/O Performance Tests using dd: https://www.thomas-krenn.com/en/wiki/Linux_I/O_Performance_Tests_using_dd
- /Benchmark disk performance using dd/
Advanced
- Understand iflags, such us fullblock
iflag=fullblockmeaning - Try to interrupt/kill your command:
dd iflag=fullblock if=/dev/urandom of=sample_output_file.txt bs=10G count=1and 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,lntruncate,fallocate,split,stat, inode, File descriptor, superblock, block size (blockdev),fuser,lsof,scrub,chattr, ulimit (nofiles),cp,mv,file (command),mkfifo,chmod
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