Linux: app doesn't start on Ubuntu 22.04 — binaries require GLIBC_2.39 #2302

Description

Cap for Linux doesn't start on Ubuntu 22.04 LTS. Clicking the app icon does nothing. When I start it from a terminal, it exits right away with this error:

$ Cap
Cap: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.39' not found (required by Cap)

Ubuntu 22.04 ships glibc 2.35. The Linux binaries require glibc 2.39, which is the version in Ubuntu 24.04, so they can't run on 22.04 or any other distro with an older glibc. Ubuntu 22.04 is still a supported LTS release and is widely used.

What I checked:

The .deb also installs without errors on 22.04 even though it can't run there, so from the user's side the app just silently does nothing.

Reproduction

1. On Ubuntu 22.04, download Cap_0.6.0_amd64.deb from cap.so/download
2. Install it with sudo apt install ./Cap_0.6.0_amd64.deb. It installs without errors.
3. Click Cap in the app menu. Nothing happens.
4. Run Cap in a terminal to see the glibc error above.
5. Optional: objdump -T /usr/bin/Cap | grep -o 'GLIBC_[0-9.]*' | sort -Vu | tail -1 prints GLIBC_2.39

Suggestions

• Build the Linux release on an older base, such as an ubuntu-22.04 runner or a manylinux-style container, so the binaries target glibc 2.35. For the AppImage, avoid bundling system libraries like libc-linked libmount/libdbus taken from a newer host.
• If that isn't possible, add a versioned glibc dependency to the .deb (for example libc6 (>= 2.39)) so apt refuses to install it, and list the minimum distro versions on the download page.

Workaround for anyone else hitting this: running the 0.6.0 .deb inside an ubuntu:24.04 Docker container, with the X11 socket, /dev/dri and the PipeWire/Pulse sockets passed through, starts the app.

Related: #1553 (Linux tracking issue)

Additional Context

• Cap version: 0.6.0 (also checked 0.5.2)
• Operating system, version: Ubuntu 22.04.5 LTS, kernel 6.8.0, X11 session, glibc 2.35
• Device (optional): x86_64, NVIDIA GeForce GTX 1650