CRAMFS was written by Linus Torvalds as a filesystem with a bare minimum feature set. It is a very simple, and sometimes simplistic, compressed and read-only filesystem aimed at
embedded systems
CRAMFS has the following limitations:
- The maximum size a file can have is 16 MB.
- There are no current (.) or parent (..) directory entries.
- The UID field for files is 16 bits wide and the GID field is 8 bits wide. Normal filesystems
- usually support either 16- or 32-bit UIDs and GIDs. On CRAMFS, GIDs are truncated to the lower 8 bits. In other words, the maximum GID usable in a root filesystem built on CRAMFS is 255
To create cramfs do following.
- Goto to <path to kernel>scripts/cramfs
- make
- Now, copy cramfsck mkcramfs to an appropriate directory.
- Now create image using these tools like
mkcramfs rootfs / images/cramfs.img
- With the filesystem image ready, we can now write it to our storage device
cat rootfs/cramfs.img > /dev/mtd4
