Update
An update is a servicing type that applies changes to an existing Trident-managed system. Like an install, it is driven by a Host Configuration file that declares the desired state. Trident compares the new Host Configuration against the currently provisioned one and automatically selects the appropriate update strategy.
For an overview of how Trident determines what to do based on the Host Configuration, see How Trident Knows What to Do.
Update Types
Trident supports two update strategies, selected automatically based on what has changed in the Host Configuration:
A/B Update
An A/B update is used when the OS image or any non-runtime-updateable configuration has changed. It provisions a complete new OS onto the inactive A/B volume while the current OS continues running, then reboots into the updated volume. See A/B Update for a detailed breakdown of what happens during an A/B update.
Runtime Update
A runtime update is used when only runtime-updateable components have changed — currently sysexts, confexts, and network configuration. Runtime updates apply changes directly to the running OS without a reboot, making them faster and less disruptive.
If any other part of the Host Configuration has changed, Trident will automatically perform an A/B update instead of a runtime update.
Operations
Like an install, an update is split into two operations:
- Stage — streams new OS images to the inactive volume (A/B) or downloads new extensions (runtime). The current workload continues running undisturbed.
- Finalize — for A/B updates, configures the UEFI BootNext variable and reboots into the updated volume. For runtime updates, activates the changes on the running OS without a reboot.
These can be run together or separately. See Two-Step Installation and Update for details on running them independently.