partx: Parse and update the kernel partition table

partx is a small, focused tool that reads a partition table and tells the kernel about it. It’s handy after creating, resizing, or attaching disk images or devices, but remember: it only affects the kernel’s view, not the disk contents.

Quick start

  • List partitions on a device or image:
sudo partx -l /dev/sdX
  • If you’re using a disk image, the path might be something like:
sudo partx -l /path/to/disk-image.img
  • Add all partitions found in a device to the kernel (with optional verbose output):
sudo partx -a -v /dev/sdX
  • For a disk image:
sudo partx -a -v /path/to/disk-image.img
  • Delete all partitions from the kernel view (does not modify the disk):
sudo partx -d /dev/sdX
  • For a disk image:
sudo partx -d /path/to/disk-image.img

Note: The -l/—list, -a/—add, and -d/—delete options can be combined with host paths that point to either a block device or a disk image.

When to use partx

  • After creating or resizing partitions on a device or disk image, to refresh the kernel’s partition table without rebooting.
  • When using loop devices or virtualization where partitions appear or disappear at runtime.

Common workflows

  1. Attach a disk image and import partitions:
# Create or attach the image, then
sudo partx -l /path/to/disk-image.img  # inspect current partitions
sudo partx -a /path/to/disk-image.img  # expose partitions to the kernel
  1. Work with a real disk after partitioning (e.g., with fdisk or parted):
sudo partx -l /dev/sdb
# make changes with your partitioning tool, then
sudo partx -a /dev/sdb  # or -d if you removed partitions
  1. Mounting and usage:
lsblk
# if new partitions don’t show up, run partx to refresh
sudo partx -a -v /dev/sdb

Safety and pitfalls

  • Do not run partx on a mounted root partition or while filesystems are mounted and in active use. Unmount first when possible.
  • partx only updates the kernel’s view. It does not modify on-disk partition tables. For a real partition table change, use a partitioning tool (fdisk/parted) and then refresh with partx.
  • If you’re using loop devices or complex storage setups, verify the correct device path before adding or deleting partitions to avoid accidental data exposure or damage.
  • After resizing or deleting partitions, you may need to run a filesystem check or resize2fs/xfs_growfs on the mounted filesystem, if applicable.

Troubleshooting tips

  • Partitions don’t appear after a change? Try listing first, then re-running add:
sudo partx -l /dev/sdX
sudo partx -a /dev/sdX
  • If a disk image is not showing expected partitions, ensure the image contains a partition table and that you’re pointing to the correct file path.
  • Kernel caching can be stubborn on some systems. A reboot is a last resort if you suspect an obscure issue, but usually a re-run of partx suffices.

Quick reference

  • List: partx -l /path/to/device_or_disk_image
  • Add: partx -a /path/to/device_or_disk_image
  • Add verbose: partx -a -v /path/to/device_or_disk_image
  • Delete: partx -d /path/to/device_or_disk_image

Remember: partx is a low-level utility for synchronizing the kernel with partition tables. Use it carefully, and prefer unmounting when dealing with mounted filesystems.

See Also