👀 MacOS dd Command for Burning ISO Images

Date Created: 2025-03-29
By: 16BitMiker
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While Linux users have their familiar tools, macOS has its own approach to creating bootable USB drives. This guide walks through the macOS-specific commands and considerations for safely using the powerful but potentially dangerous dd command to burn ISO images to USB drives.

🔍 Understanding the dd Command on macOS

The dd (data duplicator) command is a powerful Unix utility available on macOS that performs low-level copying of data. Unlike graphical tools, dd gives you precise control but requires careful handling to prevent data loss.

On macOS, there are several important differences compared to Linux:

Disk identifiers use /dev/diskN instead of /dev/sdX
The raw device path (/dev/rdiskN) offers significantly faster writes
Block size is specified as bs=1m (lowercase) rather than bs=1M

📋 Step-by-Step ISO Burning Process

🔎 Step 1: Identify Your USB Drive

First, insert your USB drive and identify it correctly:


diskutil list

The output will show all connected storage devices. Look for your USB drive, which will appear with a name like /dev/disk2 (not /dev/sdb as in Linux).

Example output:


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/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.3 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                 Apple_APFS Container disk1         500.1 GB   disk0s2

/dev/disk2 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     FDisk_partition_scheme                        *16.0 GB    disk2
   1:                 DOS_FAT_32 USB_DRIVE               16.0 GB    disk2s1

In this example, /dev/disk2 is our USB drive.

🔓 Step 2: Unmount the Drive

Before writing to the drive, you must unmount it (but not eject it):


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sudo diskutil unmountDisk /dev/diskN    # Replace N with your disk number

This unmounts all partitions on the drive while keeping the device available for writing.

💿 Step 3: Write the ISO

Now use the dd command with macOS-specific syntax:


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sudo dd if=/path/to/your.iso of=/dev/rdiskN bs=1m

Let's break down this command:

if=/path/to/your.iso - Input file: the path to your ISO image
of=/dev/rdiskN - Output file: the raw disk device (note the 'r' prefix for faster writes)
bs=1m - Block size: 1 megabyte chunks (macOS uses lowercase 'm')

📊 Step 4: Monitor Progress

Unlike Linux versions, macOS's default dd doesn't have a built-in progress indicator. You have two options:

Option 1: Press Ctrl+T during the operation to see progress statistics.

Option 2: On macOS 10.13 (High Sierra) and newer, you can use:


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sudo dd if=/path/to/your.iso of=/dev/rdiskN bs=1m status=progress

For older macOS versions, you can open another Terminal window and run:


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while pgrep -q dd; do
  kill -INFO $(pgrep dd)
  sleep 1
done

This sends an INFO signal to the dd process every second, causing it to print progress information.

🔄 Step 5: Safely Eject

After dd completes, safely eject the drive:


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sudo diskutil eject /dev/diskN

🚀 Complete Example Workflow

Here's a complete example of the process:


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# First, identify your drive
diskutil list

# Unmount the disk (example for disk2)
sudo diskutil unmountDisk /dev/disk2

# Write the ISO (using rdisk2 for faster writes)
sudo dd if=~/Downloads/debian-11.iso of=/dev/rdisk2 bs=1m

# Press Ctrl+T occasionally to check progress

# Safely eject when complete
sudo diskutil eject /dev/disk2

⚠️ Safety Precautions

The dd command is sometimes called "disk destroyer" for good reason:

TRIPLE CHECK the disk identifier before executing the command
Never use /dev/disk0 or /dev/disk1 as these are typically your system drives
Always use sudo as these operations require administrator privileges
Don't remove the USB drive until the process is complete and properly ejected
Consider making a backup of important data on the USB drive before formatting

🛠️ Troubleshooting Common Issues

"Resource busy" Error


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dd: /dev/diskN: Resource busy

Solution: Make sure you've unmounted (not ejected) the disk:


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sudo diskutil unmountDisk /dev/diskN

"Permission denied" Error


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dd: /dev/diskN: Permission denied

Solution: Use sudo to run the command with administrative privileges.

Disk "Not Readable" in Finder

If Finder shows a message that the disk is "not readable" during or after the process, this is normal. The ISO format may not be recognized by macOS's Finder.

Slow Write Speed

Solution: Make sure you're using the raw device path (/dev/rdiskN instead of /dev/diskN) for significantly faster performance.

🔄 Alternatives to dd

If you're uncomfortable with the command line or want a safer option, consider these GUI alternatives:

Balena Etcher - Cross-platform, user-friendly interface with built-in verification
USBImager - Lightweight and simple for basic ISO burning
Disk Utility - macOS's built-in tool can restore ISO images to USB drives

For Disk Utility:

Open Disk Utility
Select your USB drive in the sidebar
Click "Restore" in the toolbar
Select your ISO as the source and your USB as the destination
Click "Restore"

📚 Read More

Remember that while dd is powerful and efficient, it requires careful handling. When in doubt, GUI tools like Balena Etcher provide a safer alternative with minimal performance trade-offs.