Rust "linker `cc` not found" - Fix Missing Linker in CI

rustc uses the system C compiler (cc) as its linker, and there is no cc on the runner. The final link step of the build cannot run until a C toolchain is installed.

What this error means

Compilation gets through code generation, then fails at the link step with error: linker cc not found. The Rust toolchain itself is fine - only the OS-level linker is missing, common on slim/Alpine images.

cargo output

error: linker `cc` not found
  |
  = note: No such file or directory (os error 2)

error: could not compile `app` (bin "app") due to 1 previous error

Common causes

No C toolchain on a minimal image

Slim and Alpine base images omit a C compiler to stay small. rustc has nothing to invoke as cc for the link step.

rustup installed without a system compiler

Installing Rust via rustup does not install a linker. On a bare image you must add gcc/build-essential separately.

How to fix it

Install the C toolchain

Terminal

# Debian/Ubuntu
apt-get update && apt-get install -y build-essential
# Alpine
apk add --no-cache build-base
# RHEL/Fedora
dnf groupinstall -y "Development Tools"

Or use an alternative linker

If you install lld or mold, point Cargo at it instead of cc.

.cargo/config.toml

# .cargo/config.toml
[target.x86_64-unknown-linux-gnu]
linker = "clang"
rustflags = ["-C", "link-arg=-fuse-ld=lld"]

How to prevent it

Bake build-essential/build-base into images that compile Rust.
Use the official rust Docker image, which ships a working linker.
Document the OS-level build dependencies your project needs.