Building NSS


This page has detailed information on how to build NSS. Because NSS is a cross-platform library that builds on many different platforms and has many options, it may be complex to build._ Two build systems are maintained concurrently: a Make based and a gyp based system.


NSS needs a C and C++ compiler.  It has minimal dependencies, including only standard C and C++ libraries, plus zlib. For building, you also need make. Ideally, also install gyp-next and ninja and put them on your path. This is recommended, as the build is faster and more reliable. Please, note that we gyp is currently unmaintained and that our support for gyp-next is experimental and might be unstable.

To install prerequisites on different platforms, one can run the following commands:

On Linux:

sudo apt install mercurial git ninja-build python3-pip
python3 -m pip install gyp-next

On MacOS:

brew install mercurial git ninja python3-pip
python3 -m pip install gyp-next

It is also necessary to make sure that a python (not just python3) executable is in the path. The Homebrew Python installation has the necessary symlink but may require explicit adding to the PATH variable, for example like this:

export PATH="/opt/homebrew/opt/python/libexec/bin:$PATH"

On Windows:



To retrieve the source code from the project repositories, users will need to download a release or pull the source code with their favourite Version Control System (git or Mercurial). Installing a VCS is not necessary to build an NSS release when downloaded as a compressed archive.

By default Mozilla uses a Mercurial repository for NSS. If you whish to contribute to NSS and use git instead of Mercurial, we encourage you to install git-cinnabar.

Source code

NSS and NSPR use Mercurial for source control like other Mozilla projects. To check out the latest sources for NSS and NSPR–which may not be part of a stable release–use the following commands:

hg clone
hg clone

To get the source of a specific release, see: ref:mozilla_projects_nss_releases .

To download the source using git-cinnabar instead:

git clone hg::
git clone hg::

Build with gyp and ninja

Build NSS and NSPR using our build script from the nss directory:

cd nss

This builds both NSPR and NSS in a parent directory called dist.

Build options are available for this script: -o will build in Release mode instead of the Debug mode and -c will clean the dist directory before the build.

Other build options can be displayed by running ./ --help

Build with make

Alternatively, there is a make target, which produces a similar result. This supports some alternative options, but can be a lot slower.

USE_64=1 make -j

The make-based build system for NSS uses a variety of variables to control the build. Below are some of the variables, along with possible values they may be set to.



Build a debug (non-optimized) version of NSS. This is the default.


Build an optimized (non-debug) version of NSS.



Build for a 32-bit environment/ABI. This is the default.


Build for a 64-bit environment/ABI. This is recommended.



Do not create an AddressSanitizer build. This is the default.


Create an AddressSanitizer build.

Unit testing

NSS contains extensive unit tests.  Scripts to run these are found in the tests directory. Run the standard suite by:

HOST=localhost DOMSUF=localdomain USE_64=1 ./tests/

Unit test configuration

NSS tests are configured using environment variables. | The scripts will attempt to infer values for HOST and DOMSUF, but

can fail. Replace localhost and localdomain with the hostname and domain suffix for your host. You need to be able to connect to $HOST.$DOMSUF.

If you don’t have a domain suffix you can add an entry to /etc/hosts (on Windows,c:\Windows\System32\drivers\etc\hosts) as follows: localhost.localdomain

Validate this opening a command shell and typing: ping localhost.localdomain.

Remove the USE_64=1 override if using a 32-bit build.

Test results

Running all tests can take a considerable amount of time.

Test output is stored in tests_results/security/$HOST.$NUMBER/.  The file results.html summarizes the results, output.log captures all the test output.

Other subdirectories of nss/tests contain scripts that run a subset of the full suite. Those can be run directly instead of, which might save some time at the cost of coverage.