Ubuntu 22.04 (GTK 4.6) support: two root causes blocking build and runtime

[Taeyoung96]

Summary

Limux v0.1.4 fails to build and run on Ubuntu 22.04 (Jammy Jellyfish) for two independent reasons. This issue documents both root causes with reproduction steps, and a companion PR contains the minimal fixes.

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Root Cause 1 — gtk4-rs 0.11 API is incompatible with GTK 4.6

Background

Ubuntu 22.04 ships GTK 4.6.x as its stable GTK release. The gtk4-rs Rust crates version-match the underlying C library:

gtk4-rs crate version	Compatible GTK C version
0.6.x	GTK 4.6.x (Ubuntu 22.04)
0.7.x	GTK 4.8.x
0.8.x	GTK 4.10.x
0.9–0.11.x	GTK 4.12–4.16+

Limux v0.1.4 declares:

# rust/limux-host-linux/Cargo.toml (upstream v0.1.4)
gtk4       = { version = "0.11", features = ["v4_10"] }
gdk4-wayland = "0.11"
libadwaita  = "0.9"
webkit6     = { version = "0.6", optional = true }

What breaks

a) features = ["v4_10"] enables GTK 4.10 symbols that are absent on Ubuntu 22.04

The v4_10 feature gate enables gtk4-rs to compile in calls to symbols first introduced in GTK 4.10 (e.g. gdk_display_create_gl_context). On Ubuntu 22.04 those symbols do not exist in libgtk-4.so.1, so the linker fails.

Reproduction:

# On Ubuntu 22.04 (GTK 4.6.7)
cargo build -p limux-host-linux
# error: could not find function `gdk_display_create_gl_context` in `libgtk-4.so.1`

b) glib::Propagation and glib::ControlFlow do not exist in gtk4-rs 0.6

gtk4-rs 0.9+ replaced the signal::Inhibit type and glib::Continue with:

// gtk4-rs ≥ 0.9 (does NOT compile on 0.6):
glib::Propagation::Stop
glib::Propagation::Proceed
glib::ControlFlow::Continue

gtk4-rs 0.6 (the version that matches GTK 4.6) still uses the legacy API:

// gtk4-rs 0.6 (required for Ubuntu 22.04):
use gtk::glib::signal::Inhibit;
Inhibit(true)   // stop propagation
Inhibit(false)  // allow propagation
glib::Continue(true)  // keep timer/idle running

Attempting to build the upstream code with gtk4-rs 0.6 produces errors like:

error[E0433]: failed to resolve: use of undeclared crate or module `Propagation`
  --> src/terminal.rs:520:13
   |
   | glib::Propagation::Stop
   |       ^^^^^^^^^^^ not found in `glib`

c) libwebkitgtk-6.0-dev is not available on Ubuntu 22.04

webkit6 = { version = "0.6" } requires the libwebkitgtk-6.0-dev system package, which is only available from Ubuntu 23.04 (Lunar) onwards. On Ubuntu 22.04:

sudo apt install libwebkitgtk-6.0-dev
# E: Unable to locate package libwebkitgtk-6.0-dev

Fix

Pin the crate versions to those that match GTK 4.6 and stub out the unavailable WebKit feature:

gtk4         = { version = "0.6" }      # no version feature flags
gdk4-wayland = "0.6"
libadwaita   = "0.3"
# webkit removed; stub feature retained for build-script compatibility

Replace glib::Propagation::Stop/Proceed → Inhibit(true/false) and glib::ControlFlow::Continue → glib::Continue(true) in all signal handlers.

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Root Cause 2 — GTK 4.6 ignores set_required_version(4, 3) and always creates an OpenGL 3.2 context

Background

Ghostty's GPU renderer requires OpenGL 4.3 core profile. The natural way to request this from GtkGLArea is:

gl_area.set_required_version(4, 3);

What breaks on GTK 4.6

GTK 4.6's GDK backend honours only OpenGL 3.2 when creating the GdkGLContext for a GtkGLArea, regardless of the version requested. The required-version property is effectively ignored.

Additionally, GTK 4.6 on Ubuntu 22.04 defaults to the EGL backend even on X11 (including NVIDIA systems). glXGetCurrentDisplay() therefore returns NULL inside connect_realize, making a pure GLX fallback insufficient.

The result: Ghostty calls OpenGL 4.3 entry points (compute shaders, SSBOs, etc.) on a 3.2 context, which immediately produces GL errors and a blank/crashed terminal.

Reproduction:

# On Ubuntu 22.04 with NVIDIA GPU (GTK 4.6, EGL backend)
./target/release/limux
# Terminal pane is black / blank; stderr shows:
# GL_INVALID_OPERATION ... compute shaders require OpenGL 4.3+
# (or similar Ghostty renderer errors)

Fix

After GTK calls make_current() inside connect_realize (making the 3.2 context current), manually create an OpenGL 4.3 core context via raw EGL or GLX using dlopen/dlsym:

1. Try EGL first (GTK 4.6 default, even on X11):
   • eglGetCurrentDisplay() / eglGetCurrentContext() to obtain the current EGL state
   • eglCreateContext() requesting major=4, minor=3, core profile
2. Fall back to GLX if EGL is not active:
   • glXGetCurrentDisplay() + glXCreateContextAttribsARB() requesting 4.3

Switch to this context before each call to ghostty_surface_draw().

An environment variable LIMUX_GL_BACKEND=auto|egl|glx lets users override the backend selection when needed.

This approach works because NVIDIA's driver supports OpenGL 4.3 over both EGL and GLX; the limitation is only in GTK 4.6's GDK layer, not in the driver itself.

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Affected versions

Component	Affected	Notes
Ubuntu 22.04 (Jammy)	✅ Both root causes	GTK 4.6.7, EGL default
Ubuntu 22.10 / 23.04+	RC1 only (gtk4-rs API)	GTK 4.8+
Arch / Fedora (GTK 4.14+)	Not affected	gtk4-rs 0.11 works fine

Related

Companion PR with minimal fixes: #11

[am-will]

I have a few requests for this. I'll see what i can do about it. thanks!

[J3m5]

Related:

• Linux port: Rust + GTK4/libadwaita implementation manaflow-ai/cmux#828 (comment)
• Linux: Support Ubuntu 22.04 LTS (libadwaita 1.1) manaflow-ai/cmux#1840

[am-will]

I'm considering how to do this. also thank you @J3m5

[leelele-cug]

Any progress or plan for this issue?

[devanshwassista-10x]

@am-will Any idea what is the status on this, Is anyone actively working on it, I don't have the right experience for it, but would love to pick it up, I really want to use cmux on Ubuntu 22.04

[bvolpato]

Valid compatibility request, but Ubuntu 22.04 is not supported by current main. PR #11 closed unmerged, and current host still depends on gtk4-rs 0.11/GTK 4.10-era APIs, libadwaita 0.9, and WebKitGTK 6, which Jammy does not provide.

Pinning gtk4-rs alone is not a safe fix because UI APIs and browser runtime also change. A viable focused PR needs a rebased implementation plus reproducible Jammy build and runtime validation, including Ghostty GL context behavior and an explicit browser strategy. Keeping open as help wanted; removing good first issue because this is cross-stack compatibility work.