Rust / cargo build fails with 'error: linker `cc` not found' (or 'link.exe not found' on Windows, 'linking with cc failed'). How do I install the missing linker?

Cause: rustc compiles your code but relies on a system linker (and C toolchain) to produce the final binary. On a fresh machine, a minimal Docker image or a CI runner without build tools, there isn't one: Linux and macOS look for cc, Windows (MSVC toolchain) needs link.exe from the Visual Studio build tools. Crates that compile C code (via the cc crate, e.g. ring, openssl-sys, libsqlite3-sys) need the same toolchain. Fix (by platform, per the Rust book and rustup docs): 1. Linux: install a C compiler: on Debian/Ubuntu sudo apt install build-essential; on Fedora/RHEL sudo dnf install gcc; on Alpine apk add build-base (musl). Crates like openssl-sys may also need pkg-config and the library's -dev package. 2. macOS: install the Command Line Tools: xcode-select --install. 3. Windows (MSVC toolchain, the default): install Visual Studio Build Tools with the 'Desktop development with C++' workload (includes the MSVC linker and Windows SDK); rustup's installer offers this. Alternatively use the GNU toolchain (rustup toolchain install stable-x86_64-pc-windows-gnu), which brings its own MinGW linker. 4. In Docker, use an official rust image (it includes a C toolchain), or install the packages above in your build stage; copy only the final binary into a slim runtime image. 5. Cross-compiling: installing a target with rustup target add doesn't install a linker for that target; install the target's linker (or use a tool like cross) and set it in .cargo/config.toml under [target.<triple>] linker = ... . Verify: cc --version (or link.exe from a Developer Prompt on Windows) works, and cargo build completes. Sources: https://doc.rust-lang.org/book/ch01-01-installation.html https://rust-lang.github.io/rustup/installation/index.html