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) 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

       -v     Enable verbose messaging.

       -E     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.

       -p     Pad by 512 bytes for boot code.

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

       -z     Make explicit holes.

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

       -V, --version
              Display version information and exit.

EXIT STATUS         top

              0      success
              8      operation error, such as unable to allocate memory

SEE ALSO         top

       fsck.cramfs(8), mount(8)

AVAILABILITY         top

       The mkfs.cramfs command is part of the util-linux package and is
       available from Linux Kernel Archive 

COLOPHON         top

       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
       2021-03-21.  (At that time, the date of the most recent commit
       that was found in the repository was 2021-03-19.)  If you
       discover any rendering problems in this HTML version of the page,
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       manual page), send a mail to

util-linux                     April 2013                 MKFS.CRAMFS(8)

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