Nothing stood between "memory is tight" and "processes die at random":
the kernel OOM killer only fires after an allocation has already failed,
so a machine under pressure thrashes in reclaim until something breaks
somewhere fatal — seen in practice as Hyprland taking SIGBUS mid-memcpy
from a client shm pool that memory pressure was tearing down.
Enable systemd-oomd, which keys on PSI stall time rather than free
pages, and mark app.slice — and only app.slice — as its kill candidate.
Hyprland runs in session.slice, so the compositor is structurally
ineligible as a victim: oomd takes the app that caused the pressure and
the session survives. Thresholds (50% stall over 20s, Fedora's desktop
defaults) live in an oomd.conf.d drop-in; candidacy ships as a vendor
drop-in under /usr/lib/systemd/user so existing users get it on package
upgrade with no per-user seeding.
New installs enable the daemon from enable-services.sh; a migration
covers existing ones, restarting an already-running oomd so it doesn't
keep stale thresholds until reboot.
Deliberately not earlyoom: it triggers only when free RAM and free swap
are both under threshold, so Omarchy's large, mostly-idle swapfiles
keep it asleep through exactly this failure.
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
