Plus other improvements to the Linux service manager
Tim Anderson
Thu 1 Apr 2021 // 11:03 UTC
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Version 248 of systemd, a widely used system and service manager for Linux, adds a feature called system extension images, designed to allow system files to be added, or appear to be added, even on read-only file systems.
As developer Lennart Poettering explained: "When a system extension image is activated, its /usr/ and /opt/ hierarchies and os-release information are combined via overlayfs with the file system hierarchy of the host OS."
The primary use case for system extension images is for immutable operating systems like Red Hat's Silverblue and Kinoite. In these OSes, the file system is read-only and is updated by replacing it with a new image rather than being patched, which is better both for security and stability.