+.. SPDX-License-Identifier: GPL-2.0
- Cramfs - cram a filesystem onto a small ROM
+===========================================
+Cramfs - cram a filesystem onto a small ROM
+===========================================
-cramfs is designed to be simple and small, and to compress things well.
+cramfs is designed to be simple and small, and to compress things well.
It uses the zlib routines to compress a file one page at a time, and
allows random page access. The meta-data is not compressed, but is
expressed in a very terse representation to make it use much less
-diskspace than traditional filesystems.
+diskspace than traditional filesystems.
You can't write to a cramfs filesystem (making it compressible and
compact also makes it _very_ hard to update on-the-fly), so you have to
Hard links are supported, but hard linked files
will still have a link count of 1 in the cramfs image.
-Cramfs directories have no `.' or `..' entries. Directories (like
+Cramfs directories have no ``.`` or ``..`` entries. Directories (like
every other file on cramfs) always have a link count of 1. (There's
-no need to use -noleaf in `find', btw.)
+no need to use -noleaf in ``find``, btw.)
No timestamps are stored in a cramfs, so these default to the epoch
(1970 GMT). Recently-accessed files may have updated timestamps, but
(Flash device in physical memory map). MTD partitions based on such devices
are fine too. Then that device should be specified with the "mtd:" prefix
as the mount device argument. For example, to mount the MTD device named
-"fs_partition" on the /mnt directory:
+"fs_partition" on the /mnt directory::
-$ mount -t cramfs mtd:fs_partition /mnt
+ $ mount -t cramfs mtd:fs_partition /mnt
To boot a kernel with this as root filesystem, suffice to specify
something like "root=mtd:fs_partition" on the kernel command line.
For /usr/share/magic
--------------------
+===== ======================= =======================
0 ulelong 0x28cd3d45 Linux cramfs offset 0
>4 ulelong x size %d
>8 ulelong x flags 0x%x
>552 ulelong x fsid.blocks %d
>556 ulelong x fsid.files %d
>560 string >\0 name "%.16s"
+===== ======================= =======================
Hacker Notes