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For updates, SteamOS uses a software called RAUC to provide seamless and secure updates[1]. The update system was a major contribution by Collabora, an open-source consulting company.

RAUC uses an A/B partition system to facilitate a safe, foolproof update process. When the system boots off of Partition A, the updates will be applied to the B partition, and vice-versa. This allows the system to fallback onto another partition if one fails, either during operation or during the update process.

Despite the A/B partitions being read-only, Valve allows users to disable the Read-only Filesystem using a simple shell command. However, after an update, the modifications a user has made to the read-only filesystem are lost unless SteamOS is configured to use a folder in writeable storage to overlay the read-only storage.

RAUC Features[2]

  • Fail-Safe & Atomic
    • An update may be interrupted at any point without breaking the running system.
    • Update compatibility check
    • Atomic bootloader updates (eMMC boot partitions, MBR, GPT)
  • Cryptographic signing and verification of updates using OpenSSL (signatures based on x.509 certificates)
  • Redundancy
    • Symmetric setup (Root-FS A & B)
    • Asymmetric setup (recovery & normal)
    • Application partition, data partitions, ...
    • Allows grouping of multiple slots (rootfs, appfs) as update targets
  • Built-in network streaming mode
  • Network delta-streaming mode (using casync)
    • Chunk-based binary delta updates
    • Significantly reduce download size
    • No extra storage required
    • Bundle encryption for multiple recipients
  • Independent from update source
    • USB Stick
    • Software provisioning server (e.g. hawkBit)
  • Supports data migration
  • Network protocol support using libcurl (https, http, ftp, ssh, ...)
  • Several layers of update customization
    • Update-specific extensions (hooks)
    • System-specific extensions (handlers)
    • Fully custom update script


  1. "Portable Linux gaming with the Steam Deck". Collabora. Retrieved 2022-08-12.
  2. "RAUC - Safe and secure software updates for embedded Linux". Retrieved 2022-08-12.