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

       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
       2020-11-01.  (At that time, the date of the most recent commit that
       was found in the repository was 2020-10-21.)  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                       April 2013                   MKFS.CRAMFS(8)

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