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.DISKDEFINES

DISKDEFINES File

Linux LiveCD Disk Metadata File
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Verified by Adam B.· reviewed by FE Editorial ·updated Jul 7, 2026 2.9 (12 votes) Thanks for rating!
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A diskdefines file (usually named README.diskdefines) is a small plain-text file found at the root of Ubuntu and Debian Linux disc images. It holds a few #define lines identifying the disc name, type, and CPU architecture. Any text editor opens it. You do not need to do anything with it unless you are building a custom Linux LiveCD.

Developer: Canonical Ltd. (Ubuntu); adopted broadly in the Debian/Ubuntu ecosystem Category: Misc Files MIME: text/plain
OPENS ON Windows macOS Linux
Related: .TORRENT · .MSO · .MD5 · .SHS

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Last reviewed Jul 7, 2026

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What is the DISKDEFINES file format?

DISKDEFINES files can be found on Linux LiveCDs and LiveUSB images. README.diskdefines is the standard filename for this file. It contains information about the disc - including its name, architecture, and disc number - and is accessed by the installer. LiveCDs can also be used to boot the system directly from the disc without any installation.

LiveCD

Linux systems can be booted directly without installing to the hard drive. The system is loaded directly into RAM. A booted LiveCD can then be used to install the system on the target storage device. LiveCDs can also be used for system troubleshooting or data recovery.

The file uses C-preprocessor-style #define directives. Typical fields include DISKNAME, ARCH (such as amd64 or arm64), DISKNUM, and TOTALNUM. It is read by Ubiquity (Ubuntu) and Calamares installers to identify the disc, and by ISO creation tools like mkisofs. End users encounter it when browsing the root of a mounted Ubuntu or Debian ISO image.

Security & safety

RISK: LOW

A plain-text file with #define directives. Cannot execute; no security risk.

Format details

in a nutshell
FULL NAMELinux LiveCD Disk Metadata Fileaka README.diskdefines, disk-defines file
DEVELOPERCanonical Ltd. (Ubuntu); adopted broadly in the Debian/Ubuntu ecosystemsince ~2004 (with early Ubuntu / Debian Live CD tooling; diskdefines convention codified in Ubiquity installer)
CATEGORYMisc Files
MIME TYPEtext/plain
TYPEPlain-text metadata file found on Linux LiveCD/LiveDVD/LiveUSB disc images
RELATED.torrent.mso.md5.shs

Programs that open DISKDEFINES files

Windows1 app
Notepad Open-source Open the file in Notepad++ for syntax-highlighted plain-text viewing.
macOS1 app
TextEdit Built-in Open the file via TextEdit (plain text mode) or any macOS text editor.
Linux1 app
Any text editor (gedit, nano, vi, Kate, etc.) Built-in Open the file in any text editor; it contains plain-text #define lines.

Technical details

deep spec
EncodingPlain text (ASCII or UTF-8)
Standard filenameREADME.diskdefines (placed in the root of the ISO image)
SyntaxC-preprocessor-style #define directives
Key fieldsDISKNAME, TYPE, ARCH, DISKNUM, TOTALNUM; optional OEM and HELPURL
Typical size200 bytes - 2 KB
Developer/adopterCanonical Ltd. (Ubuntu); Debian Live ecosystem
Read byUbiquity (Ubuntu installer), Calamares (multi-distro installer), mkisofs/xorriso
Introduced~2004, with Ubuntu 4.10 (Warty Warthog) and early Debian Live tooling
Associated OSLinux; readable on any OS that can mount ISO/USB media
Location in mediaRoot directory of LiveCD/LiveDVD/LiveUSB ISO image
AuthorshipAuthored by distribution maintainers; static metadata, not generated by end-user software
Released~2004 (with early Ubuntu / Debian Live CD tooling; diskdefines convention codified in Ubiquity installer)
Specificationhelp.ubuntu.com

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Frequently asked questions

What is a README.diskdefines file?
A small plain-text file in the root of Linux ISO images (especially Ubuntu/Debian) that declares the disc name, type, and architecture. The installer reads it to display disc information. You can open it with any text editor.
Do I need this file?
End users don't need to do anything with it - it's internal metadata for the installer. It only matters if you are building or remastering a custom Linux LiveCD.
Can I delete the diskdefines file from an ISO?
Technically yes, but the Ubiquity/Calamares installer may fail to display the correct disc label or may show errors. Leave it intact in any ISO you are distributing.
How do I create a diskdefines file for my own LiveCD?
Create a plain text file named README.diskdefines with the correct #define lines (DISKNAME, TYPE, ARCH, DISKNUM, TOTALNUM), place it in the ISO root. See the Ubuntu LiveCD Customization guide for the exact format.

References

1Ubuntu Community - LiveCD Customization From Scratchhelp.ubuntu.com
2GitHub - ubuntu_livecd cookbook: README.diskdefines examplegithub.com

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