---
name: "mkfs.cramfs"
section: "8"
platform: "linux"
package: "util-linux"
version: "2.42.4-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/mkfs.cramfs"
---

# mkfs.cramfs(8)

make compressed ROM file system

## 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)](/mkcramfs/8.md)) 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)](/systemd-udevd/8.md) 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

## SEE ALSO

[**fsck.cramfs**(8)](/fsck.cramfs/8.md), [**mount**(8)](/mount/8.md)

## REPORTING BUGS

For bug reports, use the *issue tracker* \<https://github.com/util-linux/util-linux/issues\>.

## 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/\>.