sccache

Resources

Home

Package information

Article status

This article has some todo items:

• Explain how to use sccache as ccache replacement

sccache helps avoid repeated recompilation for the same C, C++, and Rust object files by fetching result from a cache directory.

Compiler cache is typically useful for:

• Developers who rebuild the same/similar codebase multiple times and use /etc/portage/patches to test patches.
• Users who frequently play with USE-flag changes and end up rebuilding the same packages multiple times.
• Users who use live ebuilds extensively.
• Installing very big ebuilds, such as www-client/firefox or mail-client/thunderbird, without fear of losing multiple hours of code compilation due to a failure.

Installation

Emerge

root #emerge --ask dev-util/sccache

Configuration

Initial setup

Important
Unlike ccache, current Portage has no direct sccache support.

Create the cache directory:

root #mkdir -p /var/cache/sccache

root #chown root:portage /var/cache/sccache

root #chmod 2775 /var/cache/sccache

Allow write access to the cache directory when running under sandbox:

FILE /etc/sandbox.d/20sccache

# Allow write access to sccache cache directory
SANDBOX_WRITE="/var/cache/sccache/"

Enable sccache support in make.conf:

FILE /etc/portage/make.conf

RUSTC_WRAPPER=/usr/bin/sccache
SCCACHE_DIR=/var/cache/sccache
SCCACHE_MAX_FRAME_LENGTH=104857600

From now on all builds utilizing Rust compiler will try to reuse object files from the /var/cache/sccache cache.

Note
SCCACHE_MAX_FRAME_LENGTH is needed to allow packages like www-client/firefox to compile.

Note
The setup above will only enable sccache usage for Rust.

General notes

sccache can be enabled for the current user and re-use the same cache directory:

FILE ~/.bashrc

export RUSTC_WRAPPER="/usr/bin/sccache"
export SCCACHE_DIR="/var/cache/sccache"
export SCCACHE_MAX_FRAME_LENGTH="104857600"

Useful variables and commands

Some variables:

• Variable SCCACHE_DIR points to cache root directory.

Some commands:

• Command sccache -s shows cache hit statistics:

user $SCCACHE_DIR=/var/cache/sccache sccache -s

Compile requests                      0
Compile requests executed             0
Cache hits                            0
Cache misses                          0
Cache timeouts                        0
Cache read errors                     0
Forced recaches                       0
Cache write errors                    0
Compilation failures                  0
Cache errors                          0
Non-cacheable compilations            0
Non-cacheable calls                   0
Non-compilation calls                 0
Unsupported compiler calls            0
Average cache write               0.000 s
Average cache read miss           0.000 s
Average cache read hit            0.000 s
Failed distributed compilations       0
Cache location                  Local disk: "/var/cache/sccache/"
Cache size                            5 GiB
Max cache size                       10 GiB

Note
Not like ccache, sccache can only read statistics from running instance. Those interested in statistics must manually spawn sccache server first.

See also

• Handbook:AMD64/Working/Features#Caching_compilation_objects — how to use Ccache
• Ccache — helps avoid repeated recompilation for the same C and C++ object files by fetching result from a cache directory.