IntroToLinux

2. Working with Blocks: The dd Command

The dd command is a powerful tool for copying and converting blocks of data. It’s often called “disk destroyer” due to its power - use carefully!

Basic dd Syntax:

dd if=input_file of=output_file [options]

Common dd Operations:

Create Files of Specific Size:

# Create 1MB file filled with zeros
dd if=/dev/zero of=test.img bs=1M count=1

# Create 100MB file
dd if=/dev/zero of=large.file bs=1M count=100

# Create file with random data
dd if=/dev/urandom of=random.dat bs=1K count=10

Backup and Restore:

# Backup entire disk (DANGEROUS - be very careful!)
dd if=/dev/sda of=disk_backup.img bs=4M

# Backup partition
dd if=/dev/sda1 of=partition_backup.img bs=4M

# Restore from backup
dd if=disk_backup.img of=/dev/sda bs=4M

# Backup with progress (using pv if available)
dd if=/dev/sda bs=4M | pv | dd of=backup.img bs=4M

Create Bootable USB:

# Create bootable USB from ISO (DANGEROUS - verify device!)
dd if=linux.iso of=/dev/sdX bs=4M status=progress

# Always sync after dd operations
sync

Performance Testing:

# Test write speed
dd if=/dev/zero of=test.img bs=1M count=1000 oflag=direct

# Test read speed  
dd if=test.img of=/dev/null bs=1M iflag=direct

dd Options:

• bs=SIZE - Block size (e.g., 1K, 1M, 1G)
• count=N - Number of blocks to copy
• skip=N - Skip N blocks at start of input
• seek=N - Skip N blocks at start of output
• status=progress - Show progress

• conv=noerror - Continue on errors

Navigation

Next: → Archiving And Compression
Previous: ← File Globbing Wildcard Patterns
Lesson Home: ↑ Lesson 6: Globbing & Archiving Course Home: ⌂ Introduction to Linux