sccache: A Shared Compiler Cache

sccache wraps the compiler like ccache but can store its cache locally, in cloud object storage, or in Redis.

sccache is Mozilla's compiler cache. It covers C, C++, Rust, and CUDA and shines when you want a shared cache backend (S3, GCS, Redis, GitHub Actions cache) instead of a per-runner directory.

What it does

sccache runs as a background server that the compiler wrapper talks to; it hashes inputs and serves cache hits from the configured backend. You wire it in by prefixing the compiler (sccache gcc) or via build-system launcher variables, the same way as ccache, but the storage backend is pluggable.

Common usage

Terminal

export RUSTC_WRAPPER=sccache              # for Rust
export CC="sccache gcc" CXX="sccache g++" # for C/C++
# CMake launcher
cmake -B build -DCMAKE_C_COMPILER_LAUNCHER=sccache \
  -DCMAKE_CXX_COMPILER_LAUNCHER=sccache
sccache --start-server                    # start the server explicitly

Options

Mechanism / Var	What it does
sccache gcc / sccache g++	Prefix the compiler invocation
CMAKE_<LANG>_COMPILER_LAUNCHER	CMake hook to run sccache
RUSTC_WRAPPER	Use sccache for cargo/rustc
SCCACHE_DIR	Local disk cache directory backend
SCCACHE_CACHE_SIZE	Maximum local cache size

In CI

For C/C++ use the launcher variables so reconfigures keep caching. Pick a backend that matches your runners: a persisted SCCACHE_DIR for single-runner setups, or a shared backend (S3/GHA cache) when many jobs should share results. Always print sccache --show-stats after the build to confirm hits.

Common errors in CI

"sccache: error: Server startup failed" often means a stale server or a port conflict; stop it with sccache --stop-server and retry. "error: failed to execute compile" with a wrapper that cannot find the compiler means CC points at sccache but the real compiler is not on PATH. If everything misses, the backend is not configured or not reachable.