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libuv is a multi-platform support library with a focus on asynchronous I/O. It was primarily developed for use by Node.js, but it's also used by Luvit, Julia, pyuv, and others.

Feature highlights

  • Full-featured event loop backed by epoll, kqueue, IOCP, event ports.

  • Asynchronous TCP and UDP sockets

  • Asynchronous DNS resolution

  • Asynchronous file and file system operations

  • File system events

  • ANSI escape code controlled TTY

  • IPC with socket sharing, using Unix domain sockets or named pipes (Windows)

  • Child processes

  • Thread pool

  • Signal handling

  • High resolution clock

  • Threading and synchronization primitives


Starting with version 1.0.0 libuv follows the semantic versioning scheme. The API change and backwards compatibility rules are those indicated by SemVer. libuv will keep a stable ABI across major releases.

The ABI/API changes can be tracked here.


libuv is licensed under the MIT license. Check the LICENSE file. The documentation is licensed under the CC BY 4.0 license. Check the LICENSE-docs file.



Official documentation

Located in the docs/ subdirectory. It uses the Sphinx framework, which makes it possible to build the documentation in multiple formats.

Show different supported building options:

$ make help

Build documentation as HTML:

$ make html

Build documentation as HTML and live reload it when it changes (this requires sphinx-autobuild to be installed and is only supported on Unix):

$ make livehtml

Build documentation as man pages:

$ make man

Build documentation as ePub:

$ make epub

NOTE: Windows users need to use make.bat instead of plain 'make'.

Documentation can be browsed online here.

The tests and benchmarks also serve as API specification and usage examples.

Other resources

  • LXJS 2012 talk — High-level introductory talk about libuv.
  • libuv-dox — Documenting types and methods of libuv, mostly by reading uv.h.
  • learnuv — Learn uv for fun and profit, a self guided workshop to libuv.

These resources are not handled by libuv maintainers and might be out of date. Please verify it before opening new issues.


libuv can be downloaded either from the GitHub repository or from the downloads site.

Starting with libuv 1.7.0, binaries for Windows are also provided. This is to be considered EXPERIMENTAL.

Before verifying the git tags or signature files, importing the relevant keys is necessary. Key IDs are listed in the MAINTAINERS file, but are also available as git blob objects for easier use.

Importing a key the usual way:

$ gpg --keyserver pool.sks-keyservers.net --recv-keys AE9BC059

Importing a key from a git blob object:

$ git show pubkey-saghul | gpg --import

Verifying releases

Git tags are signed with the developer's key, they can be verified as follows:

$ git verify-tag v1.6.1

Starting with libuv 1.7.0, the tarballs stored in the downloads site are signed and an accompanying signature file sit alongside each. Once both the release tarball and the signature file are downloaded, the file can be verified as follows:

$ gpg --verify libuv-1.7.0.tar.gz.sign

Build Instructions

For GCC there are two build methods: via autotools or via GYP. GYP is a meta-build system which can generate MSVS, Makefile, and XCode backends. It is best used for integration into other projects.

To build with autotools:

$ sh autogen.sh
$ ./configure
$ make
$ make check
$ make install

To build with CMake:

$ mkdir -p out/cmake ; cd out/cmake ; cmake -DBUILD_TESTING=ON ../..
$ make all test
# Or manually:
$ ./uv_run_tests    # shared library build
$ ./uv_run_tests_a  # static library build

To build with GYP, first run:

$ git clone https://chromium.googlesource.com/external/gyp build/gyp



  • Python 2.6 or 2.7 as it is required by GYP. If python is not in your path, set the environment variable PYTHON to its location. For example: set PYTHON=C:\Python27\python.exe
  • One of:
  • Visual C++ Build Tools
  • Visual Studio 2015 Update 3, all editions including the Community edition (remember to select "Common Tools for Visual C++ 2015" feature during installation).
  • Visual Studio 2017, any edition (including the Build Tools SKU). Required Components: "MSbuild", "VC++ 2017 v141 toolset" and one of the Windows SDKs (10 or 8.1).
  • Basic Unix tools required for some tests, Git for Windows includes Git Bash and tools which can be included in the global PATH.

To build, launch a git shell (e.g. Cmd or PowerShell), run vcbuild.bat (to build with VS2017 you need to explicitly add a vs2017 argument), which will checkout the GYP code into build/gyp, generate uv.sln as well as the necesery related project files, and start building.

> vcbuild


> vcbuild vs2017

To run the tests:

> vcbuild test

To see all the options that could passed to vcbuild:

> vcbuild help
vcbuild.bat [debug/release] [test/bench] [clean] [noprojgen] [nobuild] [vs2017] [x86/x64] [static/shared]
  vcbuild.bat              : builds debug build
  vcbuild.bat test         : builds debug build and runs tests
  vcbuild.bat release bench: builds release build and runs benchmarks


For Debug builds (recommended) run:

$ ./gyp_uv.py -f make
$ make -C out

For Release builds run:

$ ./gyp_uv.py -f make
$ BUILDTYPE=Release make -C out

Run ./gyp_uv.py -f make -Dtarget_arch=x32 to build x32 binaries.



$ ./gyp_uv.py -f xcode
$ xcodebuild -ARCHS="x86_64" -project uv.xcodeproj \
     -configuration Release -target All

Using Homebrew:

$ brew install --HEAD libuv

Note to OS X users:

Make sure that you specify the architecture you wish to build for in the "ARCHS" flag. You can specify more than one by delimiting with a space (e.g. "x86_64 i386").



For arm

$ source ./android-configure-arm NDK_PATH gyp [API_LEVEL]
$ make -C out

or for arm64

$ source ./android-configure-arm64 NDK_PATH gyp [API_LEVEL]
$ make -C out

or for x86

$ source ./android-configure-x86 NDK_PATH gyp [API_LEVEL]
$ make -C out

or for x86_64

$ source ./android-configure-x86_64 NDK_PATH gyp [API_LEVEL]
$ make -C out

The default API level is 24, but a different one can be selected as follows:

$ source ./android-configure ~/android-ndk-r15b gyp 21
$ make -C out

Note for UNIX users: compile your project with -D_LARGEFILE_SOURCE and -D_FILE_OFFSET_BITS=64. GYP builds take care of that automatically.

Using Ninja

To use ninja for build on ninja supported platforms, run:

$ ./gyp_uv.py -f ninja
$ ninja -C out/Debug     #for debug build OR
$ ninja -C out/Release

Running tests


Build (includes tests):

$ ./gyp_uv.py -f make
$ make -C out

Run all tests

$ ./out/Debug/run-tests

Run one test

The list of all tests is in test/test-list.h.

This invocation will cause the run-tests driver to fork and execute TEST_NAME in a child process:

$ ./out/Debug/run-tests TEST_NAME

This invocation will cause the run-tests driver to execute the test within the run-tests process:

$ ./out/Debug/run-tests TEST_NAME TEST_NAME

Debugging tools

When running the test from within the run-tests process (run-tests TEST_NAME TEST_NAME), tools like gdb and valgrind work normally. When running the test from a child of the run-tests process (run-tests TEST_NAME), use these tools in a fork-aware manner.

Fork-aware gdb

Use the follow-fork-mode setting:

$ gdb --args out/Debug/run-tests TEST_NAME

(gdb) set follow-fork-mode child
Fork-aware valgrind

Use the --trace-children=yes parameter:

$ valgrind --trace-children=yes -v --tool=memcheck --leak-check=full --track-origins=yes --leak-resolution=high --show-reachable=yes --log-file=memcheck.log out/Debug/run-tests TEST_NAME

Running benchmarks

See the section on running tests. The benchmark driver is out/Debug/run-benchmarks and the benchmarks are listed in test/benchmark-list.h.

Supported Platforms


AIX Notes

AIX support for filesystem events requires the non-default IBM bos.ahafs package to be installed. This package provides the AIX Event Infrastructure that is detected by autoconf. IBM documentation describes the package in more detail.

AIX support for filesystem events is not compiled when building with gyp.

z/OS Notes

z/OS creates System V semaphores and message queues. These persist on the system after the process terminates unless the event loop is closed.

Use the ipcrm command to manually clear up System V resources.


See the guidelines for contributing.