macOS Terminal Disk Commands: Complete Management Guide

Introduction

Managing disks in macOS through the graphical interface (Disk Utility) is convenient for most tasks. However, the terminal offers far greater control, especially for automation, remote work, or when the GUI is unavailable. In this guide, you will learn how to use built-in command-line utilities for disk operations: from simple free space checks to formatting and partitioning.

All commands work on modern versions of macOS (Monterey, Ventura, Sonoma). Attention: some commands, especially diskutil eraseDisk, permanently delete data. Always verify the disk identifier before performing dangerous operations.

Essential Commands for Disk Management

macOS provides several key utilities. Here are the most important ones.

diskutil: The Swiss Army knife

diskutil is the primary utility for managing disks and partitions. It replaces many functions of Disk Utility.

Key subcommands:

• diskutil list — show all disks and partitions.
• diskutil info /dev/diskX — detailed information about a disk.
• diskutil mount /dev/diskXsY — mount a partition.
• diskutil unmount /dev/diskXsY — unmount a partition.
• diskutil eraseDisk Format Name /dev/diskX — format an entire disk.
• diskutil partitionDisk /dev/diskX Format Name ... — create partitions.

df and du: Checking Space Usage

• df (disk free) shows free and used space on mounted filesystems.
  • df -h — in human-readable format (GB, MB).
  • df -i — shows inode usage (useful for "No space left on device" errors when space is available).
• du (disk usage) estimates space usage by files and directories.
  • du -sh /path/to/folder — total folder size in readable format.
  • du -h --max-depth=1 / — size of each folder in the root (requires sudo for some system folders).

mount and umount: Mount Management

• mount — show all mounted filesystems (similar to df).
• umount /dev/diskXsY — unmount a partition (legacy syntax; diskutil unmount is preferred).

Other Useful Commands

• ls /Volumes — view mounted volumes (external disks) as folders.
• diskutil verifyDisk /dev/diskX — verify disk for errors (equivalent to "First Aid").
• sudo fdisk -l — list all partitions (requires password; shows non-APFS partitions too).

Practical Examples

Viewing All Disks and Partitions

diskutil list

Output will look similar to:

/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *512.1 GB   disk0
   1:                        EFEFI EFI                     314.6 MB   disk0s1
   2:                 Apple_APFS Container disk1         511.8 GB   disk0s2

/dev/disk1 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +511.8 GB   disk1
                                 Physical Store disk0s2
   1:                APFS Volume Macintosh HD            465.3 GB   disk1s1
   2:                APFS Volume Preboot                 52.2 MB    disk1s2
   3:                APFS Volume Recovery               528.7 MB   disk1s3
   4:                APFS Volume VM                      4.2 GB     disk1s4

Note the identifiers: disk0 is the physical disk, disk1 is the APFS container, disk1s1 is a volume inside the container.

Checking Free Space on the Main Disk

df -h /

Example output:

Filesystem      Size   Used  Avail Capacity iused      ifree %iused  Mounted on
/dev/disk1s1   466G   420G   46G    91%  1000000 1000000000    0%   /

Here you can see that on the main partition (Macintosh HD), 46 GB out of 466 GB is free.

Formatting an External Disk

Warning: all data on the disk will be erased!

1. Connect the external disk.
2. Find its identifier: diskutil list. Let's say it's disk2.
3. Perform the format (e.g., in exFAT for Windows and macOS compatibility):

diskutil eraseDisk exFAT MyExternalDisk /dev/disk2

After completion, the disk will appear as MyExternalDisk in /Volumes.

Creating a New Partition on a Disk

If you have free space on a disk (e.g., disk2), you can create a new partition:

diskutil partitionDisk /dev/disk2 GPT JHFS+ NewPartition 100g

This command:

• Uses the GPT scheme.
• Creates one partition in JHFS+ (macOS Extended) format, 100 GB in size, named "NewPartition".
• Leaves the remaining space unallocated (you can create more partitions).

Mounting and Unmounting Disks

If a disk doesn't mount automatically:

diskutil mount /dev/disk2s1

For safe ejection (unmounting) before disconnecting:

diskutil unmount /dev/disk2s1

⚠️ Important: never disconnect an external disk without unmounting it via diskutil unmount or through Finder (right-click → "Eject"). This can lead to data loss.

Important Warnings

• Always verify the disk identifier (diskutil list) before any erase or partition operation. A mistake in the identifier (e.g., disk0 instead of disk2) can result in complete data loss on the system disk.
• When formatting to APFS, use APFS (or APFS (Encrypted) for encryption). For compatibility with older macOS versions, use JHFS+.
• Commands requiring superuser privileges (e.g., diskutil verifyDisk on the system disk) will ask for a password. Enter your administrator password.
• df -h shows only mounted filesystems. If a disk is connected but not mounted, it won't appear in the output. Use diskutil list to check.

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Automating Routine Tasks

The terminal allows you to create scripts for regular operations. For example, a script to check free space on all disks and send a notification if space is running low:

#!/bin/bash
# check_disk_space.sh
THRESHOLD=10 # free space percentage threshold for warning
df -h | grep -v Filesystem | while read output; do
  usage=$(echo $output | awk '{print $5}' | cut -d'%' -f1)
  partition=$(echo $output | awk '{print $6}')
  if [ $usage -ge $THRESHOLD ]; then
    echo "Warning: partition $partition has only $usage% free space left."
  fi
done

Save as check_disk_space.sh, make it executable (chmod +x check_disk_space.sh), and run it regularly via cron or launchd.

What's Next?

After mastering the basic commands, you can:

• Explore man diskutil for a full description of all options.
• Try diskutil cs (CoreStorage) for managing logical volumes (if using FileVault or older disks).
• Use hdiutil to work with disk images (creating, mounting .dmg files).
• Write more complex scripts for backups or monitoring.

Remember: with great power comes great responsibility. Always back up important data before performing disk operations.