How to build Mozc for Linux desktop

May 22, 2026 · View on GitHub

Summary

If you are not sure what the following commands do, please check the descriptions below and make sure the operations before running them.

git clone https://github.com/google/mozc.git
cd mozc/src

bazelisk build package --config release_build

bazel-bin/unix/mozc.zip contains built files.

Due to the diverse nature of Linux desktop ecosystem, continuous builds on GitHub Actions are the best example on how Mozc executables for Linux desktop can be built and tested against existing test cases.

The following sections describe relevant software components that are necessary to build Mozc for Linux desktop.

Bazelisk

Bazelisk is a wrapper of Bazel to use the specific version of Bazel.

The Bazel version specified in src/.bazeliskrc is what continuous builds are testing against.

See the following document for detail on how Bazelisk determines the Bazel version.

How does Bazelisk know which Bazel version to run?

⚠️ Bazel version mismatch is a major source of build failures. If you manually install Bazel then use it instead of Bazelisk, pay extra attention to which version of Bazel you are using.

C++ toolchain

GCC or Clang is needed to build Mozc.

While Linux continuous builds currently use GCC, Mozc's C++ code is designed to be compatible with Clang (for macOS, Windows, Android, and Google internal use).

💡 See .github/workflows/linux.yaml on which version of GCC is tested against.

💡 Like many other Bazel-based C++ projects, Mozc relies on rules_cc specified in MODULE.bazel to automatically detect C++ toolchains in the host environment.

Packages

Development packages referenced in pkg_config_repository at src/MODULE.bazel need to be installed beforehand.

# iBus
pkg_config_repository(
    name = "ibus",
    packages = [
        "glib-2.0",
        "gobject-2.0",
        "ibus-1.0",
    ],
)

# Qt for Linux
pkg_config_repository(
    name = "qt_linux",
    packages = [
        "Qt6Core",
        "Qt6Gui",
        "Qt6Widgets",
    ],
)

💡 pkg_config_repository is not a bazel standard functionality. It is a custom macro defined in src/bazel/pkg_config_repository.bzl.

Build instructions

Get the Code

You can download Mozc source code as follows.

git clone https://github.com/google/mozc.git
cd mozc/src

Hereafter you can do all the operations without changing directory.

Build Mozc

You should be able to build Mozc for Linux desktop as follows, assuming bazelisk is in your $PATH.

bazelisk build package --config release_build

package is an alias to build Mozc executables and archive them into mozc.zip.

Clean Bazel's build cache

💡 You may have some build errors when you update the build environment or configurations. Try the following command to clean Bazel's build cache.

bazelisk clean --expunge

Troubleshooting: Linker error `relocation refers to a discarded section`

If you encounter linker errors related to .sframe sections (e.g., relocation refers to a discarded section when using GCC 15+ and LLD 19+ in non-release builds), you can append --config no_sframe to disable SFrame generation:

bazelisk build package --config no_sframe

How to customize installation locations

Here is a table of contents in mozc.zip and their actual build target names.

build target	installation location
`//server:mozc_server`	`/usr/lib/mozc/mozc_server`
`//gui/tool:mozc_tool`	`/usr/lib/mozc/mozc_tool`
`//renderer:mozc_renderer`	`/usr/lib/mozc/mozc_renderer`
`//unix/ibus/ibus_mozc`	`/usr/lib/ibus-mozc/ibus-engine-mozc`
`//unix/ibus:gen_mozc_xml`	`/usr/share/ibus/component/mozc.xml`
`//unix:icons`	`/usr/share/ibus-mozc/...`
`//unix:icons`	`/usr/share/icons/mozc/...`
`//unix/emacs:mozc.el`	`/usr/share/emacs/site-lisp/emacs-mozc/mozc.el`
`//unix/emacs:mozc_emacs_helper`	`/usr/bin/mozc_emacs_helper`

To customize above installation locations, modify src/config.bzl.

💡 The following command makes the specified file untracked by Git.

git update-index --assume-unchanged src/config.bzl

💡 This command reverts the above change.

git update-index --no-assume-unchanged src/config.bzl

bazelisk test ... --build_tests_only -c dbg

... means all targets under the current and subdirectories.

Run tests under the specific directories

bazelisk test base/... composer/... --build_tests_only -c dbg

<dir>/... means all targets under the <dir>/ directory.

Run tests without the specific directories

bazelisk test ... --build_tests_only -c dbg -- -base/...

-- means the end of the flags which start from -.
-<dir>/... means exclusion of all targets under the dir.

Run the specific test

bazelisk test base:util_test -c dbg

util_test is defined in base/BUILD.bazel.

Output logs to stderr

bazelisk test base:util_test --test_arg=--stderrthreshold=0 --test_output=all

The --test_arg=--stderrthreshold=0 --test_output=all flags show the output of unitests to stderr.

Examples of environment-specific options

JDK options

bazelisk test ... --java_runtime_version=remotejdk_21

C/C++ compiler options

bazelisk test ... --repo_env=CC=gcc-14 --repo_env=CXX=g++-14

Build Mozc for Linux Desktop with GYP (deprecated):

⚠️ The GYP build is deprecated and no longer supported.

Please check the previous version for more information. https://github.com/google/mozc/blob/2.29.5374.102/docs/build_mozc_in_docker.md#build-mozc-for-linux-desktop-with-gyp-maintenance-mode