Ubuntu 26.10 Prioritizes App Termination Over Session Stability During Memory Pressure
Ubuntu's next release shifts the kernel's out-of-memory killer to target user applications first, protecting critical system services that maintain desktop sessions.
Starting with Ubuntu 26.10, the distribution is reordering how the operating system decides what to terminate when memory becomes scarce. User applications will now face removal before the core services that keep a desktop session running. Thirty-nine system services, including GNOME Shell and two D-Bus components, have been assigned an OOM score of -500, making them substantially harder targets for the kernel's out-of-memory killer.
This adjustment means that processes like web browsers consuming large amounts of memory become far more likely candidates for termination. Alongside this change, Canonical has disabled the systemd-oomd mechanism that previously could shut down an entire session under memory stress, though applications may still be terminated individually when memory runs low.
The new behavior is part of ubuntu-settings 26.10.1 and has already been deployed to the 26.10 archive.
How the kernel evaluates processes
When the system faces memory constraints, the kernel generates a ranking of all running processes. Each receives a score based on its actual memory consumption, then a user-configurable value gets added on top. This second number, which ranges from -1000 to 1000, determines kill priority—lower scores mean earlier termination.
A 2024 analysis of an Ubuntu 24.10 desktop showed GNOME Shell and Firefox both sitting at a score of 100, as did every content process Firefox created. System daemons occupied much lower positions: dbus-daemon and systemd-oomd were at -900, while systemd-journald was at -250. The incident that prompted investigation involved a logic error in custom code that spawned numerous virtual machines and exhausted available memory. The killer selected gnome-characters, a minor application, for termination while leaving the memory-hungry virtual machines untouched.
Scores represent only part of the equation
The kernel is not the sole mechanism for process termination on a desktop. systemd-oomd operates independently by monitoring memory pressure and acts sooner than the kernel, without consulting the scoring system. Ubuntu previously configured it to trigger on the user session at 50% memory pressure, meaning the new -500 scores alone would have been insufficient to prevent termination.
The ubuntu-settings patch addresses both layers. ManagedOOMMemoryPressure on user@.service now uses the "auto" setting instead of systemd-oomd's previous "kill" directive. Testing by Canonical showed that seven of ten sessions crashed without this modification, while none crashed with it applied.
Testing the changes
The updated behavior is accessible in the development release for anyone interested in evaluation. Canonical is encouraging users to test it under memory-intensive workloads on systems with limited RAM or swap space. Users encountering unexpected issues such as sudden application closures or session instability can file reports through Launchpad.