mkfs.cramfs: Create a ROM filesystem

mkfs.cramfs: Create a ROM filesystem

Overview

  • mkfs.cramfs builds a read-only, compressed ROM filesystem (CramFS) in a partition. It is lightweight and simple, but limited in features compared to modern filesystems.

Quick start

  • Create a ROM filesystem in a partition:
mkfs.cramfs /dev/sdXY
  • Create a ROM filesystem with a volume name:
mkfs.cramfs -n my_volume /dev/sdXY

Prerequisites and caveats

  • Ensure the target partition is unmounted before creating the filesystem.
  • This is a read-only filesystem once created; write operations require remaking the filesystem.
  • Back up any data on the partition, as mkfs.cramfs will overwrite existing content.
  • CramFS is older and has limited features compared to ext4, btrfs, or squashfs; verify it suits your use case.

Common pitfalls

  • Wrong device path: double-check /dev/sdXY before running mkfs. A mistaken path can wipe data on a different partition.
  • Not mounting: after creation, you must mount the filesystem to access data, e.g., mount /dev/sdXY /mnt.
  • Size expectations: cramfs does not support certain advanced features like compression tuning; rely on default behavior.

Examples in context

  • Create a ROM filesystem in /dev/sdb1:
mkfs.cramfs /dev/sdb1
  • Create with a volume name and then mount:
mkfs.cramfs -n romimage /dev/sdb1
sudo mount -t cramfs /dev/sdb1 /mnt/rom

Tips

  • Always verify the device path with lsblk or fdisk -l before running mkfs.
  • If you need writable behavior or more features, consider newer filesystems.
  • After mounting, remember that changes cannot be saved back unless you recreate the filesystem; use read-only for distribution images.

Troubleshooting

  • If mounting fails with bad filesystem type, ensure the kernel supports cramfs and that the mkfs version matches expected format.
  • Check dmesg for any filesystem-related errors after mounting.
  • If you plan to distribute this image, test portability on the target hardware to ensure cramfs compatibility.

See Also