Mastering Disk Resizing: Troubleshooting “Target is Busy” Errors with Disks GUI Utility

At revWhiteShadow, we understand the complexities that can arise when managing your storage devices, particularly when attempting intricate operations like partition resizing. The ambition to create a dual-boot environment, seamlessly integrating operating systems like macOS and Linux, is a common and powerful use case for modern computing. However, users frequently encounter frustrating roadblocks. One such pervasive issue that impedes progress is the dreaded “Disks GUI Utility - resize fails” error, often accompanied by the specific message: “unmounting file system … target is busy (udisks, error-quark, 14)”. This error, while alarming, is not insurmountable. Our aim at revWhiteShadow is to equip you with the in-depth knowledge and practical solutions needed to overcome this common hurdle, ensuring your disk management tasks are executed flawlessly.

We recognize that the convenience of a Graphical User Interface (GUI) for disk operations is highly sought after. The Disks GUI Utility, often referred to simply as “Disks” or “gnome-disk-utility,” is designed to simplify these complex tasks for users. It provides an intuitive visual representation of your storage devices, allowing for easy partition management, including resizing, formatting, and mounting/unmounting. The aspiration to resize a substantial 1TB ext4 partition to carve out space for a new macOS installation for dual-booting is a perfectly valid and achievable goal. The error message “unmounting file system … target is busy (udisks, error-quark, 14)” directly points to a core problem: the operating system, or an application running on it, is actively using the partition you are attempting to modify. This prevents the necessary unmounting process that is a prerequisite for safe resizing.

Understanding the “Target is Busy” Phenomenon

The “target is busy” error, cataloged by udisks with the error quark 14, signifies that one or more processes are currently accessing or maintaining a lock on the file system residing on the partition you intend to resize. When you initiate a resize operation through the Disks GUI Utility, the underlying system needs to unmount the target file system to ensure data integrity. If any application, service, or even background process is actively reading from or writing to this partition, the unmount command will fail, leading to the error you are experiencing.

Common culprits for this “busy” state include:

  • Mounted File Systems: The most obvious reason is that the partition itself is still mounted and in use by the running operating system. Even if you believe you’ve unmounted it, background processes might re-mount it or maintain access.
  • Running Applications: Any application that has opened files or directories on the partition will keep it busy. This could include file managers, text editors, media players, or any program that has cached data from that location.
  • Background Services: System services, such as indexing daemons, backup utilities, or system monitoring tools, might be actively interacting with the partition.
  • Swap Space: If the partition in question is being used as swap space by your Linux system, it will be persistently busy and cannot be resized while active.
  • File System Checks or Operations: If a file system check (fsck) or other maintenance operation was recently performed or is ongoing, it might keep the partition locked.
  • External Devices: In some rare cases, if the partition is on an external drive and the system suspects activity from another connected device or even a prior improper unmount, it might flag it as busy.

The Disks GUI Utility, while user-friendly, relies on the operating system’s ability to safely manipulate partitions. When the system detects that a partition is in use, it intervenes to prevent data corruption, manifesting as the “target is busy” error.

Advanced Strategies to Overcome the “Target is Busy” Error

While the Disks GUI Utility is your primary tool, sometimes a more direct approach is required to identify and terminate the processes that are holding the partition hostage. We will explore a series of methodical steps to resolve this issue, ensuring you can proceed with your dual-boot setup.

**#### Identifying Processes Holding the Partition Hostage

Before attempting any forceful actions, it’s crucial to identify which processes are actively using the partition. The command-line interface offers powerful tools for this purpose.

  1. Using lsof (List Open Files): The lsof command is invaluable for showing which files are open by which processes. To identify processes using your 1TB ext4 partition, you’ll need to know its mount point. Assuming it’s mounted at /media/youruser/your_partition_label or a similar location, you can use lsof as follows:

    sudo lsof | grep /path/to/your/ext4/mountpoint

    Replace /path/to/your/ext4/mountpoint with the actual mount point of your 1TB ext4 partition. This command will list all processes that have open files or are operating within that directory structure. Look for the output that shows processes, their PIDs (Process IDs), and the files they are accessing on the target partition.

  2. Using fuser (File User): The fuser command is specifically designed to identify processes using files or file systems. You can use it with the mount point of your partition:

    sudo fuser -m /path/to/your/ext4/mountpoint

    The -m option tells fuser to list all processes that have the specified file system mounted. The output will be a list of PIDs. You can further combine fuser with other options to get more information:

    sudo fuser -v -m /path/to/your/ext4/mountpoint

    The -v (verbose) option provides more detailed output, including the command name and the user running the process.

**#### Safely Terminating Offending Processes

Once you have identified the processes that are keeping your partition busy, you need to terminate them gracefully. Forcefully killing processes can sometimes lead to data inconsistencies, so it’s always best to try and stop them cleanly.

  1. Graceful Termination (kill command): For each PID you identified, you can try to send a SIGTERM signal, which asks the process to shut down cleanly:

    sudo kill <PID_1> <PID_2> ...

    Replace <PID_1>, <PID_2>, etc., with the actual Process IDs you found. After sending the SIGTERM, wait a few moments and then re-run your lsof or fuser command to see if the processes have terminated.

  2. Forceful Termination (kill -9): If the processes do not respond to the SIGTERM signal, you may need to use the SIGKILL signal, which forcefully terminates the process immediately:

    sudo kill -9 <PID_1> <PID_2> ...

    Use kill -9 with extreme caution. This bypasses any cleanup routines the process might have, potentially leading to data corruption if the process was in the middle of a write operation.

**#### Ensuring the Partition is Truly Unmounted

Before attempting to resize in the Disks GUI Utility, it’s vital to ensure the partition is thoroughly unmounted.

  1. Manual Unmounting via GUI: Open the Disks GUI Utility. Navigate to your 1TB ext4 partition. If it appears mounted (usually indicated by a “stop” or “unmount” icon next to it), click the “unmount” icon. If the partition is critical to the running system (e.g., your root / or /home partition), you will likely encounter the “target is busy” error here as well.

  2. Manual Unmounting via Command Line: You can also attempt to unmount it from the command line:

    sudo umount /path/to/your/ext4/mountpoint

    If this command also returns a “target is busy” error, it confirms that processes are still actively using it.

**#### The Power of the Live Environment

For operations that involve resizing the root partition (/) or other critical system partitions that cannot be cleanly unmounted while the system is running from them, the most effective and safest solution is to boot from a live USB or DVD.

A live environment (such as a Ubuntu Live USB, Fedora Live USB, etc.) runs entirely from your bootable media, meaning your primary operating system’s partitions are not actively in use by the running system. This allows you to unmount and manipulate them without encountering the “target is busy” error.

Steps to Use a Live Environment:

  1. Create a Live USB/DVD: Download an ISO image of your preferred Linux distribution (e.g., Ubuntu, Mint, Fedora) and use a tool like Rufus, Etcher, or UNetbootin to create a bootable USB drive.
  2. Boot from Live Media: Restart your computer and enter your BIOS/UEFI settings to change the boot order, prioritizing the USB drive. Save the changes and exit. Your computer will boot into the live Linux environment.
  3. Launch Disks GUI Utility: Once the live environment has loaded, open the Disks GUI Utility. It should be available in the applications menu.
  4. Access Your Internal Drives: In the Disks utility, you will see all connected storage devices, including your internal hard drive containing the 1TB ext4 partition.
  5. Select and Resize: Locate your 1TB ext4 partition. It should now be possible to unmount it without error. Once unmounted, select the resize option. You will be able to shrink the ext4 partition to create unallocated space, which you can then use to create your new macOS partition.
  6. Apply Changes: Carefully review the changes you intend to make and apply them. The resizing process can take some time, depending on the size of the partition and the speed of your storage device.
  7. Create New Partition: After shrinking the ext4 partition, create a new partition in the unallocated space. The exact file system type for the macOS partition will depend on your macOS installation requirements (often HFS+ or APFS).
  8. Reboot and Install: Once all partition operations are complete, shut down the live environment, remove the USB drive, and boot back into your primary Linux installation. You can then proceed with your macOS installation, targeting the newly created partition.

**#### Addressing Potential Issues with Swap

If your 1TB ext4 partition is being used for swap space, this will absolutely prevent it from being unmounted and resized. Swap partitions are a fundamental part of how Linux manages memory.

Steps to Disable Swap:

  1. Identify Swap Partition: You can use the swapon --show command to see if any swap is active and on which device.

    swapon --show

    If your ext4 partition or a part of it is listed here, you must disable it.

  2. Disable Swap:

    sudo swapoff /dev/sdXY

    Replace /dev/sdXY with the actual device name of your swap partition (e.g., /dev/sda3).

  3. Remove from /etc/fstab (Optional but Recommended): To prevent the system from automatically re-enabling swap on this partition after a reboot, you should also comment out or remove the corresponding line in your /etc/fstab file.

    sudo nano /etc/fstab

    Look for a line similar to: UUID=your_swap_uuid none swap sw 0 0 or /dev/sdXY none swap sw 0 0

    Add a # at the beginning of the line to comment it out. Save and exit nano (Ctrl+O, Enter, Ctrl+X).

    Crucially, remember to re-enable swap or set up a new swap space (perhaps on a different partition or as a swap file) after resizing if your system relies on it. You can re-enable it with sudo swapon /dev/sdXZ (where /dev/sdXZ is your new swap device) and add it back to /etc/fstab.

**#### The Role of Journaling in Resizing

Linux’s ext4 file system utilizes journaling to ensure data integrity. While journaling is beneficial for recovery, it can sometimes contribute to a partition appearing “busy” if the journal itself is being actively written to or if the system believes the journal state is not clean. A clean shutdown and proper unmounting are key. If you suspect journal issues, booting into a live environment and running fsck (file system check) on the partition before attempting to resize can sometimes help.

# Example using a live environment
sudo fsck -f /dev/sdXY

Replace /dev/sdXY with your ext4 partition’s device name. The -f flag forces a check even if the file system appears clean.

**#### Safeguarding Your Data: Backup is Paramount

Before undertaking any significant disk operation, especially resizing, backing up your important data is absolutely critical. While we provide these troubleshooting steps to ensure success, unforeseen events can always occur. A complete backup of your 1TB ext4 partition, or at least the most valuable files on it, will provide peace of mind and a safety net should anything go wrong. Tools like rsync, Deja Dup, or even simply copying files to an external drive can be used for this purpose.

Conclusion: Achieving Seamless Dual-Booting

The “Disks GUI Utility - resize fails” error with the “target is busy” message is a common hurdle, but one that is reliably overcome with a systematic approach. At revWhiteShadow, we advocate for understanding the root cause – active processes preventing a clean unmount – and employing the correct tools to address it.

While the Disks GUI Utility is an excellent front-end, understanding the command-line tools like lsof and fuser can provide invaluable insight into what’s preventing your operation. For critical partitions, especially the root file system, booting from a live USB/DVD environment is the most robust and safest method. It effectively removes the “target is busy” impediment by ensuring the partition is not actively used by the running operating system.

By following these detailed steps, you can confidently navigate the complexities of partition resizing, resolve the “target is busy” error, and pave the way for a successful dual-boot setup. Remember, patience, careful identification of processes, and the strategic use of a live environment are your most powerful allies in mastering your storage management. Your journey to a versatile dual-boot system is achievable, and revWhiteShadow is here to guide you through it.