README.md
1[](https://travis-ci.org/mozilla/sccache) [](https://ci.appveyor.com/project/luser/sccache2)
2
3sccache - Shared Compilation Cache
4==================================
5
6sccache is a [ccache](https://ccache.dev/)-like compiler caching tool. It is used as a compiler wrapper and avoids compilation when possible, storing cached results either on [local disk](#local) or in one of [several cloud storage backends](#storage-options).
7
8sccache includes support for caching the compilation of C/C++ code, [Rust](docs/Rust.md), as well as NVIDIA's CUDA using [nvcc](https://docs.nvidia.com/cuda/cuda-compiler-driver-nvcc/index.html).
9
10sccache also provides [icecream](https://github.com/icecc/icecream)-style distributed compilation (automatic packaging of local toolchains) for all supported compilers (including Rust). The distributed compilation system includes several security features that icecream lacks such as authentication, transport layer encryption, and sandboxed compiler execution on build servers. See [the distributed quickstart](docs/DistributedQuickstart.md) guide for more information.
11
12---
13
14Table of Contents (ToC)
15======================
16
17* [Installation](#installation)
18* [Build Requirements](#build-requirements)
19* [Build](#build)
20* [Usage](#usage)
21* [Storage Options](#storage-options)
22 * [Local](#local)
23 * [S3](#s3)
24 * [Redis](#redis)
25 * [Memcached](#memcached)
26 * [Google Cloud Storage](#google-cloud-storage)
27 * [Azure](#azure)
28* [Debugging](#debugging)
29* [Interaction with GNU `make` jobserver](#interaction-with-gnu-make-jobserver)
30* [Known Caveats](#known-caveats)
31
32---
33
34## Installation
35
36There are prebuilt x86-64 binaries available for Windows, Linux (a portable binary compiled against musl), and macOS [on the releases page](https://github.com/mozilla/sccache/releases/latest). Several package managers also include sccache packages, you can install the latest release from source using cargo, or build directly from a source checkout.
37
38### macOS
39
40On macOS sccache can be installed via [Homebrew](https://brew.sh/):
41
42```bash
43brew install sccache
44```
45
46### Windows
47
48On Windows, sccache can be installed via [scoop](https://scoop.sh/):
49
50```
51scoop install sccache
52```
53
54### Via cargo
55
56If you have a Rust toolchain installed you can install sccache using cargo. **Note that this will compile sccache from source which is fairly resource-intensive. For CI purposes you should use prebuilt binary packages.**
57
58
59```bash
60cargo install sccache
61```
62
63---
64
65Usage
66-----
67
68Running sccache is like running ccache: prefix your compilation commands with it, like so:
69
70```bash
71sccache gcc -o foo.o -c foo.c
72```
73
74If you want to use sccache for caching Rust builds you can define `build.rustc-wrapper` in the
75[cargo configuration file](https://doc.rust-lang.org/cargo/reference/config.html). For example, you can set it globally
76in `$HOME/.cargo/config` by adding:
77
78```toml
79[build]
80rustc-wrapper = "/path/to/sccache"
81```
82
83Note that you need to use cargo 1.40 or newer for this to work.
84
85Alternatively you can use the environment variable `RUSTC_WRAPPER`:
86
87```bash
88export RUSTC_WRAPPER=/path/to/sccache
89cargo build
90```
91
92sccache supports gcc, clang, MSVC, rustc, NVCC, and [Wind River's diab compiler](https://www.windriver.com/products/development-tools/#diab_compiler).
93
94If you don't [specify otherwise](#storage-options), sccache will use a local disk cache.
95
96sccache works using a client-server model, where the server runs locally on the same machine as the client. The client-server model allows the server to be more efficient by keeping some state in memory. The sccache command will spawn a server process if one is not already running, or you can run `sccache --start-server` to start the background server process without performing any compilation.
97
98You can run `sccache --stop-server` to terminate the server. It will also terminate after (by default) 10 minutes of inactivity.
99
100Running `sccache --show-stats` will print a summary of cache statistics.
101
102Some notes about using `sccache` with [Jenkins](https://jenkins.io) are [here](docs/Jenkins.md).
103
104To use sccache with cmake, provide the following command line arguments to cmake 3.4 or newer:
105
106```
107-DCMAKE_C_COMPILER_LAUNCHER=sccache
108-DCMAKE_CXX_COMPILER_LAUNCHER=sccache
109```
110
111---
112
113Build Requirements
114------------------
115
116sccache is a [Rust](https://www.rust-lang.org/) program. Building it requires `cargo` (and thus `rustc`). sccache currently requires **Rust 1.43.0**. We recommend you install Rust via [Rustup](https://rustup.rs/).
117
118Build
119-----
120
121If you are building sccache for non-development purposes make sure you use `cargo build --release` to get optimized binaries:
122
123```bash
124cargo build --release [--no-default-features --features=s3|redis|gcs|memcached|azure]
125```
126
127By default, `sccache` builds with support for all storage backends, but individual backends may be disabled by resetting the list of features and enabling all the other backends. Refer the [Cargo Documentation](http://doc.crates.io/manifest.html#the-features-section) for details on how to select features with Cargo.
128
129### Building portable binaries
130
131When building with the `gcs` feature, `sccache` will depend on OpenSSL, which can be an annoyance if you want to distribute portable binaries. It is possible to statically link against OpenSSL using the `openssl/vendored` feature.
132
133#### Linux
134
135Build with `cargo` and use `ldd` to check that the resulting binary does not depend on OpenSSL anymore.
136
137#### macOS
138
139Build with `cargo` and use `otool -L` to check that the resulting binary does not depend on OpenSSL anymore.
140
141#### Windows
142
143On Windows, the binary might also depend on a few MSVC CRT DLLs that are not available on older Windows versions.
144
145It is possible to statically link against the CRT using a `.cargo/config` file with the following contents.
146
147```toml
148[target.x86_64-pc-windows-msvc]
149rustflags = ["-Ctarget-feature=+crt-static"]
150```
151
152Build with `cargo` and use `dumpbin /dependents` to check that the resulting binary does not depend on MSVC CRT DLLs anymore.
153
154When statically linking with OpenSSL, you will need Perl available in your `$PATH`.
155
156---
157
158Storage Options
159---------------
160
161### Local
162sccache defaults to using local disk storage. You can set the `SCCACHE_DIR` environment variable to change the disk cache location. By default it will use a sensible location for the current platform: `~/.cache/sccache` on Linux, `%LOCALAPPDATA%\Mozilla\sccache` on Windows, and `~/Library/Caches/Mozilla.sccache` on MacOS.
163
164The default cache size is 10 gigabytes. To change this, set `SCCACHE_CACHE_SIZE`, for example `SCCACHE_CACHE_SIZE="1G"`.
165
166### S3
167If you want to use S3 storage for the sccache cache, you need to set the `SCCACHE_BUCKET` environment variable to the name of the S3 bucket to use.
168
169You can use `AWS_ACCESS_KEY_ID` and `AWS_SECRET_ACCESS_KEY` to set the S3 credentials. Alternately, you can set `AWS_IAM_CREDENTIALS_URL` to a URL that returns credentials in the format supported by the [EC2 metadata service](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/iam-roles-for-amazon-ec2.html#instance-metadata-security-credentials), and credentials will be fetched from that location as needed. In the absence of either of these options, credentials for the instance's IAM role will be fetched from the EC2 metadata service directly.
170
171If you need to override the default endpoint you can set `SCCACHE_ENDPOINT`. To connect to a minio storage for example you can set `SCCACHE_ENDPOINT=<ip>:<port>`. If your endpoint requires TLS, set `SCCACHE_S3_USE_SSL=true`.
172
173You can also define a prefix that will be prepended to the keys of all cache objects created and read within the S3 bucket, effectively creating a scope. To do that use the `SCCACHE_S3_KEY_PREFIX` environment variable. This can be useful when sharing a bucket with another application.
174
175
176### Redis
177Set `SCCACHE_REDIS` to a [Redis](https://redis.io/) url in format `redis://[:<passwd>@]<hostname>[:port][/<db>]` to store the cache in a Redis instance. Redis can be configured as a LRU (least recently used) cache with a fixed maximum cache size. Set `maxmemory` and `maxmemory-policy` according to the [Redis documentation](https://redis.io/topics/lru-cache). The `allkeys-lru` policy which discards the *least recently accessed or modified* key fits well for the sccache use case.
178
179### Memcached
180Set `SCCACHE_MEMCACHED` to a [Memcached](https://memcached.org/) url in format `tcp://<hostname>:<port> ...` to store the cache in a Memcached instance.
181
182### Google Cloud Storage
183To use [Google Cloud Storage](https://cloud.google.com/storage/), you need to set the `SCCACHE_GCS_BUCKET` environment variable to the name of the GCS bucket.
184If you're using authentication, either set `SCCACHE_GCS_KEY_PATH` to the location of your JSON service account credentials or `SCCACHE_GCS_CREDENTIALS_URL` with
185a URL that returns the oauth token.
186By default, SCCACHE on GCS will be read-only. To change this, set `SCCACHE_GCS_RW_MODE` to either `READ_ONLY` or `READ_WRITE`.
187
188### Azure
189To use Azure Blob Storage, you'll need your Azure connection string and an _existing_ Blob Storage container name. Set the `SCCACHE_AZURE_CONNECTION_STRING`
190environment variable to your connection string, and `SCCACHE_AZURE_BLOB_CONTAINER` to the name of the container to use. Note that sccache will not create
191the container for you - you'll need to do that yourself.
192
193**Important:** The environment variables are only taken into account when the server starts, i.e. only on the first run.
194
195---
196
197Overwriting the cache
198---------------------
199
200In situations where the cache contains broken build artifacts, it can be necessary to overwrite the contents in the cache. That can be achieved by setting the `SCCACHE_RECACHE` environment variable.
201
202---
203
204Debugging
205---------
206
207You can run the server manually in foreground mode by running `SCCACHE_START_SERVER=1 SCCACHE_NO_DAEMON=1 sccache`, and send logging to stderr by setting the [`SCCACHE_LOG` environment variable](https://docs.rs/env_logger/0.7.1/env_logger/#enabling-logging) for example
208
209 SCCACHE_LOG=debug SCCACHE_START_SERVER=1 SCCACHE_NO_DAEMON=1 sccache
210
211Alternately, you can set the `SCCACHE_ERROR_LOG` environment variable to a path and set `SCCACHE_LOG` to get the server process to redirect its logging there (including the output of unhandled panics, since the server sets `RUST_BACKTRACE=1` internally).
212
213 SCCACHE_ERROR_LOG=/tmp/sccache_log.txt SCCACHE_LOG=debug sccache
214
215---
216
217Interaction with GNU `make` jobserver
218-------------------------------------
219
220sccache provides support for a [GNU make jobserver](https://www.gnu.org/software/make/manual/html_node/Job-Slots.html). When the server is started from a process that provides a jobserver, sccache will use that jobserver and provide it to any processes it spawns. (If you are running sccache from a GNU make recipe, you will need to prefix the command with `+` to get this behavior.) If the sccache server is started without a jobserver present it will create its own with the number of slots equal to the number of available CPU cores.
221
222This is most useful when using sccache for Rust compilation, as rustc supports using a jobserver for parallel codegen, so this ensures that rustc will not overwhelm the system with codegen tasks. Cargo implements its own jobserver ([see the information on `NUM_JOBS` in the cargo documentation](https://doc.rust-lang.org/stable/cargo/reference/environment-variables.html#environment-variables-cargo-sets-for-build-scripts)) for rustc to use, so using sccache for Rust compilation in cargo via `RUSTC_WRAPPER` should do the right thing automatically.
223
224---
225
226Known Caveats
227-------------
228
229### General
230
231* Absolute paths to files must match to get a cache hit. This means that even if you are using a shared cache, everyone will have to build at the same absolute path (i.e. not in `$HOME`) in order to benefit each other. In Rust this includes the source for third party crates which are stored in `$HOME/.cargo/registry/cache` by default.
232
233### Rust
234
235* Crates that invoke the system linker cannot be cached. This includes `bin`, `dylib`, `cdylib`, and `proc-macro` crates. You may be able to improve compilation time of large `bin` crates by converting them to a `lib` crate with a thin `bin` wrapper.
236* Incrementally compiled crates cannot be cached. By default, in the debug profile Cargo will use incremental compilation for workspace members and path dependencies. [You can disable incremental compilation.](https://doc.rust-lang.org/cargo/reference/profiles.html#incremental)
237
238[More details on Rust caveats](/docs/Rust.md)
239
){kind=link}