mkfs.cramfs(8) — Linux manual page


MKFS.CRAMFS(8)            System Administration           MKFS.CRAMFS(8)

NAME         top

       mkfs.cramfs - make compressed ROM file system

SYNOPSIS         top

       mkfs.cramfs [options] directory file

DESCRIPTION         top

       Files on cramfs file systems are zlib-compressed one page at a
       time to allow random read access. The metadata is not compressed,
       but is expressed in a terse representation that is more
       space-efficient than conventional file systems.

       The file system is intentionally read-only to simplify its
       design; random write access for compressed files is difficult to
       implement. cramfs ships with a utility (mkcramfs(8)) to pack
       files into new cramfs images.

       File sizes are limited to less than 16 MB.

       Maximum file system size is a little under 272 MB. (The last file
       on the file system must begin before the 256 MB block, but can
       extend past it.)

ARGUMENTS         top

       The directory is simply the root of the directory tree that we
       want to generate a compressed filesystem out of.

       The file will contain the cram file system, which later can be

OPTIONS         top

           Enable verbose messaging.

           Treat all warnings as errors, which are reflected as command
           exit status.

       -b blocksize
           Use defined block size, which has to be divisible by page

       -e edition
           Use defined file system edition number in superblock.

       -N big, little, host
           Use defined endianness. Value defaults to host.

       -i file
           Insert a file to cramfs file system.

       -n name
           Set name of the cramfs file system.

           Pad by 512 bytes for boot code.

           This option is ignored. Originally the -s turned on directory
           entry sorting.

           Make explicit holes.

           Use exclusive BSD lock for device or file it operates. The
           optional argument mode can be yes, no (or 1 and 0) or
           nonblock. If the mode argument is omitted, it defaults to
           "yes". This option overwrites environment variable
           $LOCK_BLOCK_DEVICE. The default is not to use any lock at
           all, but it’s recommended to avoid collisions with udevd or
           other tools.

       -h, --help
           Display help text and exit.

       -V, --version
           Print version and exit.

EXIT STATUS         top


           operation error, such as unable to allocate memory

SEE ALSO         top

       fsck.cramfs(8), mount(8)

REPORTING BUGS         top

       For bug reports, use the issue tracker at

AVAILABILITY         top

       The mkfs.cramfs command is part of the util-linux package which
       can be downloaded from Linux Kernel Archive
       <>. This page
       is part of the util-linux (a random collection of Linux
       utilities) project. Information about the project can be found at
       ⟨⟩. If you have
       a bug report for this manual page, send it to This page was obtained from the
       project's upstream Git repository
       ⟨git://⟩ on
       2023-12-22. (At that time, the date of the most recent commit
       that was found in the repository was 2023-12-14.) If you discover
       any rendering problems in this HTML version of the page, or you
       believe there is a better or more up-to-date source for the page,
       or you have corrections or improvements to the information in
       this COLOPHON (which is not part of the original manual page),
       send a mail to

util-linux 2.39.594-1e0ad      2023-07-19                 MKFS.CRAMFS(8)

Pages that refer to this page: fsck.cramfs(8)systemd-makefs@.service(8)