Glossary

Everyday terms

App. A catalog entry a user can launch: content, a container specification and a launch command. A game, a desktop or a launcher.

Channel. Which platform releases an instance is offered: stable (tagged releases), beta (plus prereleases) or edge (latest branch build). Switching changes what’s listed, not what’s installed.

Console mode. A host showing sessions on a screen plugged into it. See Console mode.

Control plane. The service for accounts, the API, signaling and scheduling, backed by Postgres. Holds no per-host GPU state.

Device. A browser a user has logged in from, with its measured decode capabilities, so Quasar never sends a codec it can’t play.

Home root. The directory on a host holding managed homes. For saves to follow users between hosts it must be shared storage.

Host. A machine running the node agent.

Launch profile. An ordered list of stream profiles, best first. What “1080p60” means in the interface.

Library provider. A source of automatically discovered games. Currently Steam only.

Managed home. A user’s persistent directory for one app. One writer at a time, so one session per user per app.

Node agent. The service on each GPU host. Runs the compositor, encoder and app containers.

Readiness check. One verdict about a host, with a fix when it fails. Some failing checks block launches until fixed or overridden.

Runtime preset. A reusable container specification shared by apps.

Session. One user, one app, one host, one connection.

Stream profile. The database row behind one encode rung: codec, resolution, frame rate, bitrate and eligibility thresholds. See Rung. Users don’t see these.

Advanced technical terms

ABR. Adaptive bitrate: moves the encoder’s target bitrate to fit the connection. On by default, in smooth mode.

Admission. The check that a GPU can take a new session: a free encode slot and enough free GPU memory.

Attempt. One target (the control plane or a host) moving to one set of images. Every apply records one, and it’s the only record of what ran before.

AV1. A modern codec using 40 to 50 percent less bitrate than H.264. Compatibility depends on your browser, device and GPU host; see Codecs.

Constrained baseline. The H.264 profile browser sessions use, because Chrome can’t decode High profile over WebRTC.

Developer apply. An admin applying unpublished image digests (such as a branch build) to one Quasar-owned machine. Never automatic; same safety rules as any update.

Diagnostic bundle. A window of a session’s metrics and events with an automated verdict. Attach it to bug reports.

DMABuf. The Linux mechanism for passing a frame to the VA-API encoder without copying it.

Encode slot. One unit of concurrent encoding capacity on a GPU.

Entitlement. The grant that puts an app in a user’s library: for everyone or named users.

Engine mode. Whether the container engine runs as root (rootful) or as an ordinary account (rootless).

Engine profile. A platform, container engine and engine mode combination, rated supported, experimental or unsupported. See Container engines.

Enrollment token. A single-use secret from Fleet ▸ Hosts ▸ Add host that lets one agent enroll. Expires after an hour by default (up to 30 days); the agent then uses its own node secret.

FEC. Forward error correction: redundancy to rebuild lost packets. Off by default; not recommended for browsers.

Fleet run. One release applied across the instance: control plane first, then each eligible host. Skipped hosts aren’t failures; a failed target stops the run.

Floor. The oldest node agent and recovery actor a control-plane release still manages. A host below it is offered only the update that lifts it.

GOP. Group of pictures: frames between keyframes. Default 60.

Hand-over. The recovery actor replacing itself. The successor takes over only after it verifies; otherwise the previous actor is restored.

H.264. The baseline codec. Decodes everywhere, and every quality tier ends in an H.264 rung.

HEVC. H.265. 30 to 40 percent less bitrate than H.264, but Chrome decodes it only with OS hardware support (macOS, Windows). The catalog says hevc, the wire h265.

Home claim. Where one user’s home for one app lives. Once it exists, that app launches on that host for that user. An admin can release the claim of a host that’s gone for good.

Host preparation. The few host commands an install needs, run once as root: the engine at boot and NVIDIA wiring for a rootful install (Docker); the quasar account and its device access for a rootless one.

ICE. How WebRTC finds a network path between peers. Stuck at “checking” means no path worked.

Install mode. How a host got its images: from the registry, built from source, or owned (managed by its recovery actor). Source-built hosts aren’t updated from the console.

Intra refresh. A rolling wave of intra-coded blocks instead of periodic keyframes. Vulkan only, patched image only.

Machine state. The quasar-machine volume: the machine’s inputs, secrets, update records and pre-update dumps. It lets recovery work while the control plane is down. Never delete it.

NVENC. NVIDIA’s hardware encoder.

Owner conflict. A Quasar-like container not created by this installation, such as a leftover Compose stack. The recovery actor won’t touch it.

Placement. Choosing the host and GPU for a session, limited by home claims, the app’s host selection and readiness, then ordered by QUASAR_PLACEMENT_POLICY.

Platform release. Quasar’s own images (control plane, node agent, recovery actor) built from one commit and published together, with a floor. Not the seed, Postgres or app images.

Playout buffer. The client’s jitter buffer. Uneven frame arrival makes it bigger, which adds latency.

Pre-update dump. A dump of Quasar’s own database taken before a migrating update, restorable with one printed restore command. The last three are kept. Your own database gets none; you confirm your backup instead.

Presentation interval variation. Standard deviation of the gap between displayed frames; tracks perceived stutter. Below 12 ms is healthy, above 18 ms visible.

Recovery actor. The quasar-recovery container on each machine. It creates and replaces the machine’s Quasar services, including the control plane.

Release manifest. The machine-readable list of a stable release’s images, by digest, and their commit.

Render node. The GPU device under /dev/dri used for compositing and encoding. Prefer /dev/dri/by-path/ names; numbered names can change on reboot.

Replacement. Moving one service to a new image: start the new one, verify it, then remove the old one, or restore it if verification fails.

Rung. One stream profile inside a launch profile.

Seed. The one container you declare for Quasar on a machine. It keeps the recovery actor running. Your stack manager updates it, not Quasar, and removing it never stops Quasar.

Signaling. The exchange over /v1/signal that lets a browser and a node agent set up a direct connection.

STUN and TURN. WebRTC NAT traversal and relaying. Quasar ships no ICE relay: media goes directly, over a LAN or VPN. An experimental, unsupported QUASAR_ICE_SERVERS knob exists; leave it unset.

VA-API. The video acceleration interface for AMD and Intel encoding.

Vulkan encoder. The Vulkan Video encode path, the default on AMD and NVIDIA, for H.264, HEVC and AV1.

Wayland compositor. The gst-wayland-display element games render into; it produces the frames that are encoded.

WebRTC. The browser technology carrying video, audio and input between client and GPU host.

Zero copy. Passing frames from compositor to encoder without going through system memory.