The error is happening because `audiopus_sys` falls back to building Opus from source, but the build environment doesn’t have cmake installed. That’s why you see: `failed to execute command: No such file or directory (os error 2)` `is cmake not installed?` I believe to fix this, you need to update your `nixpacks.toml` so `cmake` is included in `nixPkgs` along with `pkg-config`, and keep `opus` in `nixLibs` Example: `[phases.setup]` `nixPkgs = [` ` "cmake",` ` "pkg-config"` `]` `nixLibs = [` ` "opus"` `]` After redeploying with this config, the build should succeed! 🙂

Few things: 1. `opus` is not a valid Nix library or package 2. The crate should not even be attempting to build libopus; the intended behavior is that the presence of `pkg-config` and the libopus is sufficient for the crate discover it and statically link to it. 3. The proposed solution (including keeping `libopus` as a library) fails similarly to the original failure: \`\`\` process didn't exit successfully: `/app/target/release/build/audiopus_sys-9601873073ea72a2/build-script-build` (exit status: 101) \--- stdout cargo:info=Static feature or environment variable found. cargo:rerun-if-env-changed=OPUS\_NO\_PKG\_CONFIG cargo:rerun-if-env-changed=PKG\_CONFIG\_x86\_64-unknown-linux-gnu cargo:rerun-if-env-changed=PKG\_CONFIG\_x86\_64\_unknown\_linux\_gnu cargo:rerun-if-env-changed=HOST\_PKG\_CONFIG cargo:rerun-if-env-changed=PKG\_CONFIG cargo:rerun-if-env-changed=PKG\_CONFIG\_PATH\_x86\_64-unknown-linux-gnu cargo:rerun-if-env-changed=PKG\_CONFIG\_PATH\_x86\_64\_unknown\_linux\_gnu cargo:rerun-if-env-changed=HOST\_PKG\_CONFIG\_PATH cargo:rerun-if-env-changed=PKG\_CONFIG\_PATH cargo:rerun-if-env-changed=PKG\_CONFIG\_LIBDIR\_x86\_64-unknown-linux-gnu cargo:rerun-if-env-changed=PKG\_CONFIG\_LIBDIR\_x86\_64\_unknown\_linux\_gnu cargo:rerun-if-env-changed=HOST\_PKG\_CONFIG\_LIBDIR cargo:rerun-if-env-changed=PKG\_CONFIG\_LIBDIR cargo:rerun-if-env-changed=PKG\_CONFIG\_SYSROOT\_DIR\_x86\_64-unknown-linux-gnu cargo:rerun-if-env-changed=PKG\_CONFIG\_SYSROOT\_DIR\_x86\_64\_unknown\_linux\_gnu cargo:rerun-if-env-changed=HOST\_PKG\_CONFIG\_SYSROOT\_DIR cargo:rerun-if-env-changed=PKG\_CONFIG\_SYSROOT\_DIR cargo:info`pkg_config` could not find `Opus`. cargo:info=Opus source path used: "/root/.cargo/registry/src/[index.crates.io](http://index.crates.io)\-1949cf8c6b5b557f/audiopus\_sys-0.2.2/opus". cargo:info=Building Opus via CMake. CMAKE\_TOOLCHAIN\_FILE\_x86\_64-unknown-linux-gnu = None CMAKE\_TOOLCHAIN\_FILE\_x86\_64\_unknown\_linux\_gnu = None HOST\_CMAKE\_TOOLCHAIN\_FILE = None CMAKE\_TOOLCHAIN\_FILE = None CMAKE\_GENERATOR\_x86\_64-unknown-linux-gnu = None CMAKE\_GENERATOR\_x86\_64\_unknown\_linux\_gnu = None HOST\_CMAKE\_GENERATOR = None CMAKE\_GENERATOR = None CMAKE\_PREFIX\_PATH\_x86\_64-unknown-linux-gnu = None CMAKE\_PREFIX\_PATH\_x86\_64\_unknown\_linux\_gnu = None HOST\_CMAKE\_PREFIX\_PATH = None CMAKE\_PREFIX\_PATH = None CMAKE\_x86\_64-unknown-linux-gnu = None CMAKE\_x86\_64\_unknown\_linux\_gnu = None HOST\_CMAKE = None CMAKE = None running: cd "/app/target/release/build/audiopus\_sys-69cb3deaefc852a0/out/build" && CMAKE\_PREFIX\_PATH="" LC\_ALL="C" "cmake" "/root/.cargo/registry/src/[index.crates.io](http://index.crates.io)\-1949cf8c6b5b557f/audiopus\_sys-0.2.2/opus" "-DCMAKE\_INSTALL\_PREFIX=/app/target/release/build/audiopus\_sys-69cb3deaefc852a0/out" "-DCMAKE\_C\_FLAGS= -ffunction-sections -fdata-sections -fPIC -m64" "-DCMAKE\_C\_COMPILER=/root/.nix-profile/bin/cc" "-DCMAKE\_CXX\_FLAGS= -ffunction-sections -fdata-sections -fPIC -m64" "-DCMAKE\_CXX\_COMPILER=/root/.nix-profile/bin/c++" "-DCMAKE\_ASM\_FLAGS= -ffunction-sections -fdata-sections -fPIC -m64" "-DCMAKE\_ASM\_COMPILER=/root/.nix-profile/bin/cc" "-DCMAKE\_BUILD\_TYPE=Release" \--- stderr thread 'main' panicked at /root/.cargo/registry/src/[index.crates.io](http://index.crates.io)\-1949cf8c6b5b557f/cmake-0.1.54/src/[lib.rs:1119](http://lib.rs:1119):5: failed to execute command: No such file or directory (os error 2) is `cmake` not installed? build script failed, must exit now note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace warning: build failed, waiting for other jobs to finish... \`\`\`

Aaaah! I see. Thank you for that good explanation. Maybe try updating your `nixpacks.toml` like so if you haven't tried this already: `[phases.setup]` `nixPkgs = [` ` "cmake",` ` "pkg-config",` ` "libopus"` `]` `pkg-config` should detect the system `libopus` and link against it. Let me know how that goes!

This works even if cmake is removed. Thank you for noticing that.