Peekaboo Linux Gnome Wayland Computer Use

peekaboo-linux-gnome-wayland-computer-use

The Linux/Wayland counterpart to macOS computer-use — "see and poke the screen of a box for troubleshooting or automation." On macOS that's trivial (CGWindowList + CGEvent + AX tree). On GNOME/Wayland it's locked down by design, but it can be made to work end-to-end:

• See → gnome-screenshot (re-enabled on GNOME 49+ via a small GNOME extension).
• Act → ydotool (writes to /dev/uinput, no root).
• Target elements → AT-SPI WINDOW-relative extents + the Window Calls extension's window origin, composed into real absolute click coordinates (works where naive AT-SPI returns (0,0)).
• Hands-on (optional) → GNOME Remote Desktop in Remote-Login mode for a human at an RDP client.

Both the "see" and "act" sides work natively (an agent process running ON the box) and remotely (from another machine over SSH). A native agent is a single actor — it can screenshot, analyze, then ydotool-click in one loop. No second machine, no human, no RDP roundtrip.

Context tags below — [NATIVE] = an agent process running ON the GNOME box (sharing the desktop session of user@1000); [REMOTE] = on another machine, reaching the box over SSH.

Verified on Ubuntu 26.04 LTS + GNOME Shell 50 (Wayland), NVIDIA + AMD multi-GPU, multi-monitor. Substitute your own host/user where the examples use USER@HOST and /run/user/UID.

Capability matrix

Target environment assumptions

• A GNOME/Wayland box with a logged-in graphical session (the GUI session must be active on a seat).
• For remote use: SSH access (key-based recommended), and the box's session env exported in non-login shells — XDG_RUNTIME_DIR=/run/user/UID, DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/UID/bus, WAYLAND_DISPLAY=wayland-0, DISPLAY=:0. (Replace UID with the session user's numeric id, e.g. 1000.)
• If agents run under systemd --user with the full graphical session env + lingering enabled, they inherit all of the above and survive SSH disconnects.
• gnome-screenshot grabs the full virtual desktop (all monitors stitched). On multi-4K setups that's huge — use -w (focused window) or the per-display helper below.

CAPABILITY A — Screenshot (the key unlock)

GNOME 49+ revoked gnome-screenshot's access to the private Shell screenshot API, so on a stock box every headless capture path is dead (see "why" below). The fix is the allow-gnome-screenshot extension (https://github.com/siddhpant/allow-gnome-screenshot, GNOME 49/50): it re-adds org.gnome.Screenshot to the Shell's _senderChecker._allowlistMap, so the gnome-screenshot binary specifically regains access. It is scoped to that one sender — it does NOT enable global unsafe_mode.

[NATIVE] — just call it (session env already present):

gnome-screenshot -f /tmp/shot.png        # full virtual desktop (all monitors)
gnome-screenshot -w -f /tmp/shot.png     # focused window only (smaller)
gnome-screenshot -a -f /tmp/shot.png     # interactive area (needs a human at the screen — avoid headless)
# then hand /tmp/shot.png to your image-analysis step

[REMOTE] — over SSH, then pull it back:

ssh USER@HOST '
  export XDG_RUNTIME_DIR=/run/user/UID DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/UID/bus
  gnome-screenshot -f /tmp/shot.png'
scp USER@HOST:/tmp/shot.png /tmp/   # then analyze it

Sanity-check the capture — a 4K full-desktop PNG is ~15-20 MB; a tiny/near-empty file or an all-black image means the extension got disabled or the session dropped to the GDM greeter. Quick non-black check: python3 -c "from PIL import Image; im=Image.open('/tmp/shot.png').convert('RGB'); d=list(im.getdata()); print(sum(1 for p in d[::997] if p!=(0,0,0)))" → should be well >0.

Installing the extension from scratch

# [NATIVE or over SSH with the session env exported]
sudo apt-get install -y gnome-screenshot
D=~/.local/share/gnome-shell/extensions/allow-gnome-screenshot@siddh.me
git clone --depth 1 https://github.com/siddhpant/allow-gnome-screenshot.git /tmp/ags
mkdir -p "$D" && cp -r /tmp/ags/allow-gnome-screenshot@siddh.me/* "$D/"
sudo systemctl restart gdm3      # reload the Shell so it discovers the extension (see WARNING below)
# after the session returns:
export XDG_RUNTIME_DIR=/run/user/UID DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/UID/bus
gnome-extensions enable allow-gnome-screenshot@siddh.me
gnome-extensions info allow-gnome-screenshot@siddh.me | grep State   # expect ACTIVE

Per-display capture (capture ONE monitor, not the stitched canvas)

gnome-screenshot -f grabs the entire virtual desktop. On multi-monitor setups that's a huge, mostly-empty canvas. To get a single clean display, use the bundled screenshot-display helper (scripts/screenshot-display.py). It reads live monitor geometry from Mutter DisplayConfig and crops the full capture to the chosen monitor.

screenshot-display --list                               # enumerate monitors + geometry
screenshot-display --monitor primary --out /tmp/p.png   # primary (default)
screenshot-display --monitor DP-4   --out /tmp/m.png    # by connector name
screenshot-display --monitor 2      --out /tmp/m.png    # by index (0-based, sorted L->R, T->B)
screenshot-display --monitor active --out /tmp/w.png    # the FOCUSED WINDOW (best "being worked on" signal)

Each per-monitor crop is a clean single-display image — feed it straight to your vision step. [REMOTE]: run screenshot-display over SSH (export the session env), then scp the output back.

Window targeting — screenshot a specific program / the display it's on

Shell.Eval/Introspect are locked, but the Window Calls extension (https://github.com/ickyicky/window-calls, GNOME 45-50) exposes window list + geometry over D-Bus at /org/gnome/Shell/Extensions/Windows. The screenshot-display helper uses it to find and crop to a window or its monitor:

screenshot-display --list-windows                       # wm_class, id, focus, monitor, title
screenshot-display --window focused      --out /tmp/w.png   # crop to focused window's exact rect
screenshot-display --window "wm_class=firefox" --out /tmp/w.png  # match by wm_class substring
screenshot-display --window "title=Settings"   --out /tmp/w.png  # match by title substring
screenshot-display --window-display focused        --out /tmp/d.png  # the whole MONITOR that window sits on
screenshot-display --window-display "wm_class=Code" --out /tmp/d.png  # monitor a matched window is on

Flow: List → pick window (focused / wm_class / title) → Details gives x,y,width,height,monitor → helper crops the full capture to the window rect, or to whichever monitor's rect contains the window's center. (Details works; GetFrameBounds is broken in this ext version — the helper doesn't use it.)

Full setup/enablement guide to replicate on any GNOME/Wayland box: references/peekaboo-and-rdp-setup-ubuntu-gnome-wayland.md.

CAPABILITY B — Input injection (ydotool)

ydotool writes to /dev/uinput below the display server (the input analog of the screenshot unlock). Install it, run ydotoold as a persistent user service (socket /run/user/UID/.ydotool_socket), and ACL /dev/uinput to your user (no root needed at runtime).

[NATIVE]:

export YDOTOOL_SOCKET=/run/user/UID/.ydotool_socket
ydotool mousemove -a 960 540     # absolute pixel coords (no element targeting)
ydotool click 0xC0               # left click down+up
ydotool type "hello"
ydotool key 28:1 28:0            # Enter (keycode:press / keycode:release)

[REMOTE]:

ssh USER@HOST '
  export XDG_RUNTIME_DIR=/run/user/UID YDOTOOL_SOCKET=/run/user/UID/.ydotool_socket
  ydotool mousemove -a 700 400; ydotool click 0xC0; ydotool type "hi"'

If ydotoold.service is down — systemctl --user enable --now ydotoold.service. For element targeting (not blind coords) use the locate-element helper below.

CAPABILITY B+ — Click an element by role/name (SOM via hybrid coords)

You do NOT need blind pixel guessing or a vision round-trip for most clicks. The bundled locate-element helper (scripts/locate-element.py) resolves a UI element to a real absolute coordinate and clicks/types it.

Why it works when AT-SPI looks broken: on Wayland, getExtents(SCREEN) returns (0,0) for GTK4/Electron (no global coordinates by design), so naive AT-SPI clicking fails. But getExtents(WINDOW) (widget-relative) is populated, and Window Calls gives the window's screen origin from Mutter's privileged view. The helper composes them: abs = window_origin + window_relative_extents + size/2. Proven on GTK4 apps.

locate-element --app gnome-text-editor --list                       # list elements + computed ABS coords
locate-element --app gnome-text-editor --role text --click          # click first text widget
locate-element --app org.gnome.Nautilus --name "New Folder" --click  # click by visible label
locate-element --app gnome-text-editor --role text --click --type "hello"   # click then type
locate-element --window-id 1367000216 --role "push button" --name Open --click  # by explicit window id
locate-element --app firefox --name Reload --print                  # just print "X Y", act yourself

• --app matches the AT-SPI app name AND wm_class loosely (normalizes org.gnome.TextEditor ↔ gnome-text-editor).
• --role/--name are case-insensitive substring filters; --index N picks the Nth match.
• Needs toolkit-accessibility=true (gsettings set org.gnome.desktop.interface toolkit-accessibility true), Window Calls active, and ydotoold running.

Vision fallback (only when an element zeros even WINDOW extents — custom-drawn canvases, some Electron internals): locate-element exits non-zero and prints the fallback recipe — screenshot-display --window 'wm_class=X' --out /tmp/w.png → analyze for pixel coords → ydotool mousemove -a -x X -y Y.

Deep dive on the technique, the gotchas, and why Newton isn't a substitute yet: references/wayland-atspi-hybrid-som.md.

The native loop (single actor — the whole point)

[NATIVE agent on the box]
  1. gnome-screenshot -f /tmp/s.png
  2. analyze /tmp/s.png  → "the Save button is at ~(1820, 640)"
  3. ydotool mousemove -a 1820 640 && ydotool click 0xC0
  4. gnome-screenshot again → verify it landed

No second machine, no human, no RDP. For element targeting prefer locate-element over blind coords.

Window actions (focus / move / resize / close)

Window Calls also does focus/move/resize/close verbs (window id from --list-windows):

WIN=/org/gnome/Shell/Extensions/Windows
gdbus call --session --dest org.gnome.Shell --object-path $WIN --method $WIN.Activate <id>   # focus/raise
gdbus call --session --dest org.gnome.Shell --object-path $WIN --method $WIN.Move <id> <x> <y>
gdbus call --session --dest org.gnome.Shell --object-path $WIN --method $WIN.Resize <id> <w> <h>
gdbus call --session --dest org.gnome.Shell --object-path $WIN --method $WIN.Maximize <id>
gdbus call --session --dest org.gnome.Shell --object-path $WIN --method $WIN.Close <id>

Flow: Activate <id> → screenshot-display --window focused → ydotool interact.

CAPABILITY C — Live interactive desktop via RDP (optional, for a human)

For a person to drive the desktop hands-on from another machine, use GNOME Remote Desktop in Remote Login mode (system/headless, fresh negotiated display — NOT Desktop Sharing, which mirrors the physical multi-monitor desktop and re-hits the huge-canvas problem).

• Mode: grdctl --system (system service gnome-remote-desktop.service, enabled at boot).
• Listener: *:3389 — always LAN-scope it in your firewall, never any-source.
• TLS cert at /var/lib/gnome-remote-desktop/rdp-tls.{crt,key}.
• Credentials: a device user + password over NLA. Setting the device cred = the Linux user's password makes both stages (NLA device prompt, then GDM login) take the same credential.

Connect from a client (Microsoft Remote Desktop / Windows App, or any RDP client) → HOST → device user/pass → GDM → sign in as the Linux user.

⚠️ #1 RDP gotcha — credential changes need a daemon restart. grdctl --system rdp set-credentials writes the keyfile but the running daemon does NOT hot-reload it into its NTLM SAM. Until you sudo systemctl restart gnome-remote-desktop.service, NLA fails for every client: ntlm_fetch_ntlm_v2_hash: Could not find user in SAM database → SEC_E_NO_CREDENTIALS → transport_accept_nla: client authentication failure. Meanwhile grdctl status shows the correct creds (it reads the file). Clients report this as FREERDP_ERROR_CONNECT_TRANSPORT_FAILED (RoyalTS) or ERRCONNECT_AUTHENTICATION_FAILED (FreeRDP) — looks like transport/cert, is actually stale creds. Fix: set creds (password via STDIN) → restart the service → verify journald shows no SAM/ NO_CREDENTIALS errors. Server requires NLA (HYBRID_REQUIRED_BY_SERVER) — expected.

Diagnosing any RDP auth failure: read the SERVER's journald, not the client error string. Client errors all collapse different server causes into the same opaque message. Full server-log→cause map, the +auth-only//sec:tls client probes, the cert/listener sanity checks, AND the empty-server-log case (tcpdump proves client-vs-network — e.g. a GUI client completing TCP then sending zero RDP bytes = client-side engine fault, fixed by recreating the connection, not touching the server): references/rdp-auth-diagnosis-server-side.md.

For automated capture you do NOT need RDP — Capability A is simpler. RDP is for a human. Full setup steps: references/peekaboo-and-rdp-setup-ubuntu-gnome-wayland.md (Step 7).

Why the stock capture paths fail (so you don't waste time re-testing)

1. gnome-screenshot WITHOUT the extension → exit 0 but no file (AccessDenied to the private API under the hood).
2. Raw gdbus/busctl call to org.gnome.Shell.Screenshot → AccessDenied. The extension allowlists the gnome-screenshot binary's D-Bus name, not arbitrary callers — so capture must go through the gnome-screenshot binary, not a hand-rolled gdbus call.
3. xdg-desktop-portal Screenshot → no Response even with the PermissionStore granted (forced interactive dialog).
4. org.gnome.Mutter.ScreenCast.CreateSession → Session creation inhibited (gated to grd itself).
5. ffmpeg kmsgrab (KMS framebuffer) → "No usable planes" on NVIDIA proprietary KMS. /dev/fb0 → all-black (GNOME doesn't scan out to fb0).
6. grim → wlroots-only, fails on Mutter. Don't apt install grim.
7. enable unsafe_mode via gdb injection into gnome-shell → CRASHES the Shell, drops the desktop to the GDM greeter. Do NOT use the gdb method. The extension is the safe, scoped, persistent unlock.

No usable screen-coordinate accessibility on Wayland — AT-SPI getExtents(SCREEN) is (0,0) on GTK4/Electron. BUT this is solved by Capability B+ (locate-element): WINDOW-relative AT-SPI extents + Window Calls window origin → real click coords. Use locate-element for "click element labeled Save"; fall back to vision-locate only where even WINDOW extents are zero.

Pitfalls

• The screenshot unlock is binary-scoped — only the gnome-screenshot binary is allowlisted. A raw gdbus Screenshot call still fails. Always shell out to gnome-screenshot.
• Reloading the Shell on Wayland = restarting GDM (sudo systemctl restart gdm3). There's no in-place Alt+F2 r over SSH. The live GUI session is briefly torn down, so don't do it mid-GUI-task. If autologin is enabled the desktop recovers in ~12s; systemd --user services survive if lingering is on. Verify recovery: loginctl list-sessions shows a seat0 Type=wayland Active=yes session.
• Never use the gdb unsafe_mode injection — it crashes gnome-shell. Use the extension.
• The allow-gnome-screenshot extension can silently flip to INACTIVE (its allowlist hook only re-arms on a fresh Shell init). Symptom: gnome-screenshot -f exits 0 but writes no file. A disable/enable cycle is NOT enough — it needs a Shell reload (sudo systemctl restart gdm3) to re-arm. If you depend on capture in an automated loop, verify the file exists each time and reload-on-miss. (Window Calls can flip too — re-enable after any GDM restart.)
• gnome-screenshot -a (interactive area) needs a human at the screen — useless headless; use -f (full) or -w (window).
• Full-desktop shots are huge (multi-4K). Prefer -w, or downscale before analysis.
• ydotool needs ydotoold alive + YDOTOOL_SOCKET/XDG_RUNTIME_DIR. Re-enable if it dies. Raw ydotool is blind absolute pixels — prefer locate-element (Capability B+) for element targeting.
• A detached SSH session isn't fully in the graphical session — export XDG_RUNTIME_DIR=/run/user/UID (+ DBUS) explicitly. A native systemd --user service already has it.
• Always LAN-scope RDP (3389) and SSH (22) in your firewall — never any-source.