Configuration

kache reads configuration from three places, in order of priority:

1. Environment variables — always win, useful for CI overrides
2. Config file — selected from the config file priority below
3. Defaults — sensible values that work without any configuration

Config file

The config file is TOML. You can edit it directly or use the TUI editor:

kache config

The TUI editor shows all fields with their current values, marks which ones are coming from env vars, and lets you toggle or edit them interactively.

Config file priority:

1. KACHE_CONFIG, when set
2. The nearest project-local .kache.toml, walking up from the current directory
3. User config at ~/.config/kache/config.toml, respecting XDG_CONFIG_HOME

A minimal config that enables a remote cache looks like this:

[cache.remote]
type = "s3"
bucket = "my-build-cache"
endpoint = "https://s3.example.com"   # omit for AWS S3
profile = "my-aws-profile"            # omit to use the default credential chain

All settings

Environment variable	Config key	Default	Description
KACHE_CACHE_DIR	cache.local_store	~/Library/Caches/kache on macOS, ~/.cache/kache on Linux	Local cache directory
KACHE_MAX_SIZE	cache.local_max_size	50GiB	Maximum local store size
KACHE_CONFIG	—	XDG config path	Explicit config file path
KACHE_S3_BUCKET	cache.remote.bucket	—	S3 bucket name
KACHE_S3_ENDPOINT	cache.remote.endpoint	—	S3 endpoint URL (required for Ceph, MinIO, R2)
KACHE_S3_REGION	cache.remote.region	us-east-1	AWS region
KACHE_S3_PREFIX	cache.remote.prefix	artifacts	Key prefix inside the bucket
KACHE_S3_PROFILE	cache.remote.profile	—	AWS credentials profile
KACHE_S3_ACCESS_KEY	—	—	Explicit S3 access key
KACHE_S3_SECRET_KEY	—	—	Explicit S3 secret key
KACHE_CACHE_EXECUTABLES	cache.cache_executables	false	Cache bin/dylib/cdylib/proc-macro outputs
KACHE_CLEAN_INCREMENTAL	cache.clean_incremental	true	Auto-clean tracked incremental dirs during GC; active builds also remove the current crate's incremental dir eagerly
—	cache.exclude	[]	Source-path glob patterns that bypass kache and compile normally without lookup, store, or upload
KACHE_COMPRESSION_LEVEL	cache.compression_level	3	Zstd compression level (1–22)
KACHE_S3_CONCURRENCY	cache.s3_concurrency	16	Max concurrent S3 operations
KACHE_S3_POOL_IDLE_SECS	cache.s3_pool_idle_secs	300	How long an idle S3 connection is kept in the HTTP pool. Higher values reuse warm TLS sessions across build phases; lower this if you sit behind a load balancer that drops idle connections aggressively
KACHE_DAEMON_IDLE_TIMEOUT	cache.daemon_idle_timeout_secs	600	Idle daemon shutdown timeout in seconds (0 disables auto-shutdown)
KACHE_DISABLED	—	0	Disable caching entirely (pass-through to rustc)
KACHE_LOG	—	kache=warn	Log level for stderr output
KACHE_LOG_FILE	—	kache=info	Log level for the file log
KACHE_PROGRESS	—	auto	CI progress lines: always, never, or auto

KACHE_PROGRESS=auto (the default) prints per-crate progress lines to stderr when stderr is not a terminal. In CI this is usually the right behavior without any configuration.

Excluding Sources

Use cache.exclude when a source file should compile normally but never use kache:

[cache]
exclude = [
  "crates/problematic-rust-crate/**",
  "vendor/problematic-c-lib/**",
  "$CARGO_HOME/registry/src/**/some-crate-*/**",
]

Patterns are globs matched against the compiler's primary source path. Relative patterns are matched relative to the current build directory and, when kache can infer it, the Cargo workspace root. Excluded invocations bypass local lookup, remote lookup, store, and upload.

Exclude patterns support ~, $VAR, and ${VAR} expansion. $CARGO_HOME falls back to Cargo's default ~/.cargo when the environment variable is not set, so registry-source exclusions work on default Cargo installs.

Credential resolution order

Remote S3 credentials are resolved in this order:

1. KACHE_S3_ACCESS_KEY + KACHE_S3_SECRET_KEY
2. AWS profile from cache.remote.profile or KACHE_S3_PROFILE
3. AWS default chain, such as AWS_ACCESS_KEY_ID, ~/.aws/credentials [default], or IAM roles

For Ceph, MinIO, or R2, set cache.remote.endpoint or KACHE_S3_ENDPOINT.

[cache.remote]
type = "s3"
bucket = "build-cache"
endpoint = "https://s3.example.com"
profile = "ceph"

Size values

Size fields (KACHE_MAX_SIZE, cache.local_max_size) accept human-friendly strings:

50GiB   10GB   512MiB   1024MB

Log levels

KACHE_LOG follows the tracing subscriber syntax:

KACHE_LOG=kache=debug   # verbose, useful when diagnosing cache misses
KACHE_LOG=kache=info    # operational detail
KACHE_LOG=kache=warn    # default — only surface real problems

The file log is written to ~/Library/Logs/kache/kache.log on macOS and ~/.cache/kache/kache.log elsewhere. It rotates automatically when it exceeds 5 MB.

Local store layout

~/.cache/kache/           # Linux example
├── index.db          # SQLite index (WAL mode)
├── events.jsonl      # build event log
├── daemon.sock       # daemon unix socket
└── store/            # content-addressed blobs
    ├── ab/
    │   └── abcdef...  # blake3 hash-named files
    └── ...

The store directory is excluded from Time Machine and Spotlight on macOS automatically.