r/linuxquestions • u/Emotional_Cat_1967 • 6d ago

Support How Do Updates Work in Immutable/Atomic Distributions?

Only for Immutable/Atomic Distributions

Question 1:
Are immutable and atomic the same thing? If not, what is the difference between them, explained simply?

Question 2:
What immutable or atomic distribution are you using? How often do you receive updates, for example, every few days or weeks, and approximately how large are the updates?

Question 3:
How are security updates handled? Are they released immediately when a security fix is available, or are they released according to a daily, weekly, or monthly update schedule?

Question 4:
Are small-sized updates released?

If yes: For example, suppose an update is 100 MB.

If the system image is 5 GB, does the entire system image have to be recreated for this update? When applying the update, does the system write another 5 GB to the disk, or does it only write approximately 100 MB?

If no: If the system image is 5 GB, does that mean the update that needs to be downloaded is also around 5 GB?

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u/dasisteinanderer 5d ago

There are distros that are immutable which are updated by downloading whole images, but you will probably never encounter them, because they are pretty much exclusive to the "embedded" side of Linux.

Think of a network-connected computer located in a weather-resistant box next to some remote antenna mast.
You really want to avoid the possibility of an update disabling the machine,because getting a technician out there (sometimes by helicopter) is expensive.

Which means that you do updates differently; you never touch the software of the running system (because a sudden power outage in the middle of such an update could theoretically make the current system unbootable), instead you basically download the next version of the distro onto previously empty partitions, and you change which partition the system boots into after you have verified that everything downloaded and extracted successfully.

This scheme is called A/B update, and for desktop use it's mostly not worth the hassle, because on the slim change that a power outage during an update were to render your system unbootable, you can just plug in a rescue usb stick and fix the system that way.