# mkfs.cramfs

## NAME



           mkfs.cramfs - make compressed ROM file system
    


## SYNOPSIS



           **mkfs.cramfs**[options] _directory file_
    


## DESCRIPTION



           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



           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
           mounted.
    


## OPTIONS



           **-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
               size.
    
           **-e** _edition_
               Use defined file system edition number in superblock.
    
           **-N big** |**little** |**host**
               Use the specified endianness. The default is **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.
    
           **-l**[**=**_mode_]
               Use an exclusive BSD lock for the device or file that is
               operated upon. The optional argument _mode_ can be **yes**(**1**), **no**
               (**0**), or **nonblock**. If the _mode_ argument is omitted, it defaults
               to **yes**. This option overrides the environment variable
               **$LOCK_BLOCK_DEVICE**. The default is to not use any lock at all,
               but using a lock is recommended to avoid collisions with
               systemd-udevd(8) or other tools.
    
           **-h** , **--help**
               Display help text and exit.
    
           **-V** , **--version**
               Display version and exit.
    


## EXIT STATUS



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


## AVAILABILITY



           The **mkfs.cramfs** command is part of the util-linux package which
           can be downloaded from Linux Kernel Archive
           <https://www.kernel.org/pub/linux/utils/util-linux/>. This page is
           part of the _util-linux_ (a random collection of Linux utilities)
           project. Information about the project can be found at 
           ⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩. If you have a
           bug report for this manual page, send it to
           util-linux@vger.kernel.org. This page was obtained from the
           project's upstream Git repository
           ⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
           2025-08-11. (At that time, the date of the most recent commit that
           was found in the repository was 2025-08-05.) 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 man-pages@man7.org
    
    util-linux 2.42-start-521-ec46  2025-08-09                 _MKFS.CRAMFS_(8)
    


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