Complete Disk Backup and Restore with dd Command

The dd command is a powerful Linux utility for creating exact bit-by-bit copies of disks, partitions, or files. This guide covers how to safely create full disk backups and restore them when needed.

⚠️ Important Safety Warning

dd is dangerous! A single typo can permanently destroy your data. Always:

  • Double-check your input (if=) and output (of=) devices
  • Ensure you’re backing up the correct disk
  • Never run dd on a mounted filesystem
  • Keep backups on a separate physical drive
  • Test your backups before you need them

The dd command is nicknamed “disk destroyer” for good reason—use it carefully!

Prerequisites

  • Root or sudo access
  • Sufficient disk space for backup (at least equal to source disk size)
  • External drive or network storage for backup storage
  • Basic understanding of Linux disk naming (/dev/sda, /dev/sdb, etc.)

Finding Your Disks

List All Disks

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# List all disks and partitions
sudo fdisk -l

# Or use lsblk for a tree view
lsblk

# Check disk usage
df -h

Understanding disk names:

  • /dev/sda - First SATA/SCSI disk (entire disk)
  • /dev/sda1 - First partition on first disk
  • /dev/nvme0n1 - First NVMe SSD
  • /dev/mmcblk0 - SD card
  • /dev/sdb - Second disk (usually external USB)

Important: Back up the entire disk (e.g., /dev/sda), not just a partition (e.g., /dev/sda1). This ensures bootloader and partition table are included.

Identify Your Source Disk

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# Check mounted disks
mount | grep "^/dev"

# Get detailed disk information
sudo fdisk -l /dev/sda

Creating a Disk Backup

Basic Disk to Image Backup

Create a complete disk image file:

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# Backup entire disk to image file
sudo dd if=/dev/sda of=/path/to/backup/full_disk_backup.img bs=4M status=progress

Parameters explained:

  • if=/dev/sda - Input file (source disk to backup)
  • of=full_disk_backup.img - Output file (backup image)
  • bs=4M - Block size of 4 megabytes (faster than default)
  • status=progress - Shows progress during copy

Example with real paths:

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# Backup to external USB drive
sudo dd if=/dev/sda of=/media/usb/backups/laptop_backup_2025-12-29.img bs=4M status=progress

Direct Disk to Disk Backup

Clone one disk directly to another (faster, no intermediate file):

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# Copy disk /dev/sda to disk /dev/sdb
sudo dd if=/dev/sda of=/dev/sdb bs=4M status=progress

Warning: This will completely erase /dev/sdb! Triple-check your device names!

Compressed Backup (Saves Space)

Compress the backup on-the-fly using gzip or pigz:

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# Compress with gzip (slower, better compression)
sudo dd if=/dev/sda bs=4M status=progress | gzip -c > /path/to/backup/disk_backup.img.gz

# Compress with pigz (parallel gzip, faster on multi-core CPUs)
sudo dd if=/dev/sda bs=4M status=progress | pigz -c > /path/to/backup/disk_backup.img.gz

# Lower compression for speed (level 1-9, default 6)
sudo dd if=/dev/sda bs=4M status=progress | gzip -1 > /path/to/backup/disk_backup.img.gz

Compression comparison:

  • No compression: Fastest, but huge file (entire disk size)
  • gzip -9: Slowest, smallest file (~30-50% reduction)
  • pigz -1: Good balance of speed and size

Backup Only Used Space (with dd_rescue)

For large disks with little data, use ddrescue to skip empty blocks:

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# Install ddrescue
sudo apt install gddrescue

# Backup with intelligent copying
sudo ddrescue -f -n /dev/sda /path/to/backup/disk_backup.img /path/to/backup/disk_backup.log

Optimizing dd Performance

Choosing Block Size

Block size affects speed significantly:

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# Too small (slow)
bs=512    # 512 bytes - very slow

# Good choices (fast)
bs=4M     # 4 megabytes - good default
bs=8M     # 8 megabytes - faster for large disks
bs=16M    # 16 megabytes - fastest, but uses more RAM

# Separate read/write sizes
bs=4M conv=sync,noerror  # Continue on read errors

Recommendation: Use bs=4M for most cases, bs=8M or bs=16M for very large disks.

Monitor Progress

If you forgot status=progress, monitor dd in another terminal:

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# Find dd process ID
ps aux | grep dd

# Send USR1 signal to show progress
sudo kill -USR1 <pid>

# Or use this one-liner
watch -n 5 'sudo kill -USR1 $(pgrep ^dd$)'

Speed Test

Benchmark your disk before backing up:

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# Write speed test (creates 1GB test file)
dd if=/dev/zero of=/path/to/testfile bs=1M count=1024 oflag=direct

# Read speed test
dd if=/path/to/testfile of=/dev/null bs=1M count=1024 iflag=direct

# Clean up
rm /path/to/testfile

Restoring from Backup

Restore Image to Disk

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# Restore uncompressed image
sudo dd if=/path/to/backup/full_disk_backup.img of=/dev/sdb bs=4M status=progress

# Restore compressed image (gzip)
gunzip -c /path/to/backup/disk_backup.img.gz | sudo dd of=/dev/sdb bs=4M status=progress

# Restore compressed image (pigz)
pigz -dc /path/to/backup/disk_backup.img.gz | sudo dd of=/dev/sdb bs=4M status=progress

Critical reminders:

  • /dev/sdb will be completely overwritten
  • Unmount the target disk first
  • For boot disks, connect only ONE boot disk at a time
  • Verify device names with lsblk before running

Restore Specific Partition

To restore just one partition:

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# Backup single partition
sudo dd if=/dev/sda1 of=/path/to/backup/partition_backup.img bs=4M status=progress

# Restore single partition
sudo dd if=/path/to/backup/partition_backup.img of=/dev/sdb1 bs=4M status=progress

Verification

Always verify your backups!

Compare Backup to Original

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# Calculate checksums
md5sum /dev/sda > original.md5
md5sum /path/to/backup/disk_backup.img > backup.md5

# Compare
diff original.md5 backup.md5

# Or use cmp for bit-by-bit comparison
sudo cmp /dev/sda /path/to/backup/disk_backup.img

Mount and Test Backup

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# Create loop device from backup
sudo losetup -f -P /path/to/backup/disk_backup.img

# Check which loop device was created
sudo losetup -a

# Mount partition from backup (assume /dev/loop0p1)
sudo mkdir /mnt/backup_test
sudo mount /dev/loop0p1 /mnt/backup_test

# Browse backup
ls /mnt/backup_test

# Unmount and cleanup
sudo umount /mnt/backup_test
sudo losetup -d /dev/loop0

Safety Best Practices

Before Creating Backup

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# 1. Unmount the source if possible
sudo umount /dev/sda1

# 2. Check available space on destination
df -h /path/to/backup

# 3. Test destination is writable
touch /path/to/backup/test && rm /path/to/backup/test

# 4. Double-check device names
lsblk

Before Restoring Backup

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# 1. List all disks to confirm target
lsblk

# 2. Unmount target disk
sudo umount /dev/sdb*

# 3. Confirm you have the right backup
ls -lh /path/to/backup/

# 4. TRIPLE CHECK device names!
echo "Restoring to: /dev/sdb"
echo "Press Ctrl+C to cancel or Enter to continue"
read

Common Use Cases

Backup Before System Upgrade

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# Backup boot disk before major upgrade
sudo dd if=/dev/sda of=/media/external/pre-upgrade-backup.img bs=4M status=progress

Clone Disk to Larger Disk

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# 1. Clone to larger disk
sudo dd if=/dev/sda of=/dev/sdb bs=4M status=progress

# 2. Expand partition to use new space
sudo parted /dev/sdb
(parted) print free
(parted) resizepart 2 100%
(parted) quit

# 3. Resize filesystem
sudo resize2fs /dev/sdb2  # For ext4
# or
sudo xfs_growfs /dev/sdb2  # For XFS

Backup SD Card (Raspberry Pi)

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# Find SD card device (usually /dev/mmcblk0 or /dev/sdb)
lsblk

# Backup SD card
sudo dd if=/dev/mmcblk0 of=~/backups/raspberrypi_backup.img bs=4M status=progress

# Compress
gzip ~/backups/raspberrypi_backup.img

# Restore to new SD card
gunzip -c ~/backups/raspberrypi_backup.img.gz | sudo dd of=/dev/mmcblk0 bs=4M status=progress

Create Bootable USB from ISO

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# Copy ISO to USB drive
sudo dd if=~/Downloads/ubuntu-24.04.iso of=/dev/sdb bs=4M status=progress oflag=sync

Troubleshooting

“No space left on device”

Problem: Destination doesn’t have enough space.

Solution:

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# Check available space
df -h /path/to/backup

# Use compression to reduce size
sudo dd if=/dev/sda bs=4M | gzip > backup.img.gz

# Or backup to network drive
sudo dd if=/dev/sda bs=4M | ssh user@server 'cat > /backups/disk.img'

“Device is busy”

Problem: Disk is mounted or in use.

Solution:

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# Check what's using the device
sudo lsof | grep /dev/sda

# Unmount all partitions
sudo umount /dev/sda*

# Force unmount if needed
sudo umount -l /dev/sda1

“Operation not permitted”

Problem: Insufficient permissions.

Solution:

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# Run with sudo
sudo dd ...

# Check if disk is write-protected
hdparm -r /dev/sda

dd Seems Stuck

Problem: No progress visible.

Solution:

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# Check if dd is actually running
ps aux | grep dd

# Send signal to show progress
sudo kill -USR1 $(pgrep ^dd$)

# Monitor I/O
iostat -x 2

Backup File Too Large

Problem: Image file is huge.

Solution:

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# Use compression
sudo dd if=/dev/sda bs=4M | gzip -1 > backup.img.gz

# Or backup only used blocks with partclone
sudo partclone.ext4 -c -s /dev/sda1 -o backup.partclone

# Or use rsync for incremental backups
sudo rsync -aAXv --delete / /media/backup/

Alternative Tools

While dd is powerful, consider these alternatives for specific needs:

For system backups:

  • rsync - Incremental backups, faster than dd for used space only
  • tar - Archive specific directories
  • Clonezilla - GUI tool, intelligent cloning
  • timeshift - System snapshots (like macOS Time Machine)

For disk cloning:

  • ddrescue - Recovers data from failing disks
  • partclone - Copies only used blocks (smaller backups)
  • fsarchiver - Filesystem-level backup

For disk imaging:

  • partimage - Creates partition images
  • g4u - Ghost for Unix
  • redo rescue - Live CD for backups

Quick Reference

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# Basic backup
sudo dd if=/dev/sda of=backup.img bs=4M status=progress

# Compressed backup
sudo dd if=/dev/sda bs=4M | gzip > backup.img.gz

# Direct clone
sudo dd if=/dev/sda of=/dev/sdb bs=4M status=progress

# Restore from backup
sudo dd if=backup.img of=/dev/sdb bs=4M status=progress

# Restore from compressed backup
gunzip -c backup.img.gz | sudo dd of=/dev/sdb bs=4M status=progress

# Show progress of running dd
sudo kill -USR1 $(pgrep ^dd$)

# Verify backup
md5sum /dev/sda backup.img

# Mount backup image
sudo losetup -f -P backup.img
sudo mount /dev/loop0p1 /mnt/test

Conclusion

The dd command is an essential tool for complete disk backups and disaster recovery. Key takeaways:

  • Always verify device names before running dd
  • Use compression to save space (gzip or pigz)
  • Add status=progress to monitor progress
  • Test your backups before you need them
  • Keep backups on separate physical drives
  • Consider alternatives like rsync for incremental backups

Remember: dd is powerful but dangerous. One wrong command can destroy your data permanently. Always double-check your commands before pressing Enter!