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romfs file format

.romfs  ·  filesystem image  ·  introduced 1997 by Janos Farkas

What is a romfs file?

romfs is an ultra-minimal read-only Linux filesystem designed for boot disks and initramfs in 1997. Beyond Linux, the Nintendo 3DS and Switch use a related "RomFS" variant inside cartridge dumps, so the term shows up in the homebrew console scene too.

Most readers reach this page after double-clicking a .romfs file and finding their operating system unsure what to do with it. The good news: romfs is a well-understood format with mature tooling on every major platform. It is supported in one click by mainstream archivers on Windows, macOS, and Linux.

How to extract a romfs file

Opening a .romfs file is straightforward on every modern operating system. The exact steps depend on which platform you are on:

On Windows

  1. Locate the .romfs file in File Explorer.
  2. Right-click the file. If you have 7-Zip installed, choose 7-Zip → Extract Here. On Windows 11 the built-in extractor handles ZIP, 7z, RAR and several other formats directly through Extract All…
  3. If prompted, pick a destination folder and click Extract.
  4. The extracted files appear in a folder next to the original archive.

On macOS

  1. Find the .romfs file in Finder.
  2. Install The Unarchiver from the Mac App Store, or Keka for both creating and extracting.
  3. Right-click the file → Open With → The Unarchiver (or just double-click after Unarchiver is set as the default).
  4. The extracted folder appears next to the archive.

On Linux

  1. Use your file manager: right-click the archive → Extract Here (file-roller on GNOME, Ark on KDE).
  2. On the command line, run one of: 
    7z x archive.romfs    # works for almost any format
  3. The files appear in the current directory.

How to create a romfs file

To pack files into a .romfs archive, you typically need an archiver that supports writing this format. Not every tool can create every format — for example, only WinRAR can create real RAR files. The sidebar lists the software known to read and write romfs.

On the command line, the canonical create command is:

# Use 7-Zip, PeaZip, or the format's reference tool to create .romfs files.

If you regularly create archives at scale, a dedicated archive automation suite can wrap this command in scheduled jobs, integrity checks, and offsite replication.

Strengths

  • Minimal overhead
  • Trivial format

Weaknesses and limitations

  • No compression
  • Read-only

Typical use cases

  • Linux boot disks
  • Nintendo 3DS / Switch homebrew

Technical details

romfs uses the None algorithm and is identified on disk by the magic byte sequence 2D 72 6F 6D 31 66 73 2D. The standard MIME type is application/x-romfs. The format is an open specification and is free for any use.

Frequently asked questions

Is romfs safe to open?

Archive files are containers — they are only as safe as what they contain. A .romfs from a trusted source is fine; one received from a stranger can hold malicious executables, scripts, or files engineered to exploit bugs in your archiver. Always keep your archiver updated, and never run unknown executables that come out of an archive. A safe workflow is to extract into a sandbox and scan the contents before opening anything.

What is the maximum file size?

Modern implementations support archives in the multi-terabyte range. The practical limit is your filesystem (FAT32 caps at 4 GB; ext4, NTFS, APFS, and exFAT all comfortably handle multi-TB files).

Can I password-protect a romfs?

Some archivers can wrap romfs files in an encrypted container, but the format itself does not always include built-in encryption. Check your archiver's documentation.

How does romfs compare to other formats?

See our format comparison pages such as ZIP vs 7z, ZIP vs RAR, and tar.gz vs tar.xz for side-by-side feature tables.

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