UBI / UBIFS file format

.ubi · .ubifs · filesystem image · introduced 2008 by Linux MTD project

What is a UBI / UBIFS file?

UBIFS is the Unsorted Block Image File System for raw flash, the modern successor to JFFS2. A typical embedded build creates a UBIFS image, wraps it in a UBI volume layout, and flashes the result to a NAND chip. Firmware reverse engineers use ubi_reader to extract files from .ubi blobs found in router updates.

Most readers reach this page after double-clicking a .ubi file and finding their operating system unsure what to do with it. The good news: UBI / UBIFS 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 UBI / UBIFS file

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

On Windows

Locate the .ubi file in File Explorer.
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…
If prompted, pick a destination folder and click Extract.
The extracted files appear in a folder next to the original archive.

On macOS

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

On Linux

Use your file manager: right-click the archive → Extract Here (file-roller on GNOME, Ark on KDE).

On the command line, run one of:

7z x archive.ubi    # works for almost any format

The files appear in the current directory.

How to create a UBI / UBIFS file

To pack files into a .ubi 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 UBI / UBIFS.

On the command line, the canonical create command is:

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

Faster mount than JFFS2
Wear leveling
Per-volume compression

Weaknesses and limitations

Complex layered tooling
Embedded use only

Typical use cases

Modern embedded Linux firmware
Industrial control devices

Technical details

UBI / UBIFS uses the zlib / LZO / Zstandard algorithm and is identified on disk by the magic byte sequence 55 42 49 23. The standard MIME type is application/x-ubi. The format is an open specification and is free for any use.

Frequently asked questions

Is UBI / UBIFS safe to open?

Archive files are containers — they are only as safe as what they contain. A .ubi 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 UBI / UBIFS?

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

How does UBI / UBIFS 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.