Running tests with kunit_tool

We can either run KUnit tests using kunit_tool or can run tests manually, and then use kunit_tool to parse the results. To run tests manually, see: Run Tests without kunit_tool. As long as we can build the kernel, we can run KUnit.

kunit_tool is a Python script which configures and builds a kernel, runs tests, and formats the test results.

Run command:

./tools/testing/kunit/ run

We should see the following:

Configuring KUnit Kernel ...
Building KUnit kernel...
Starting KUnit kernel...

We may want to use the following options:

./tools/testing/kunit/ run --timeout=30 --jobs=`nproc --all`
  • --timeout sets a maximum amount of time for tests to run.

  • --jobs sets the number of threads to build the kernel.

kunit_tool will generate a .kunitconfig with a default configuration, if no other .kunitconfig file exists (in the build directory). In addition, it verifies that the generated .config file contains the CONFIG options in the .kunitconfig. It is also possible to pass a separate .kunitconfig fragment to kunit_tool. This is useful if we have several different groups of tests we want to run independently, or if we want to use pre-defined test configs for certain subsystems.

To use a different .kunitconfig file (such as one provided to test a particular subsystem), pass it as an option:

./tools/testing/kunit/ run --kunitconfig=fs/ext4/.kunitconfig

To view kunit_tool flags (optional command-line arguments), run:

./tools/testing/kunit/ run --help

Creating a .kunitconfig file

If we want to run a specific set of tests (rather than those listed in the KUnit defconfig), we can provide Kconfig options in the .kunitconfig file. For default .kunitconfig, see: A .kunitconfig is a minconfig (a .config generated by running make savedefconfig), used for running a specific set of tests. This file contains the regular Kernel configs with specific test targets. The .kunitconfig also contains any other config options required by the tests (For example: dependencies for features under tests, configs that enable/disable certain code blocks, arch configs and so on).

To create a .kunitconfig, using the KUnit defconfig:

cp tools/testing/kunit/configs/default.config .kunit/.kunitconfig

We can then add any other Kconfig options. For example:


kunit_tool ensures that all config options in .kunitconfig are set in the kernel .config before running the tests. It warns if we have not included the options dependencies.


Removing something from the .kunitconfig will not rebuild the .config file. The configuration is only updated if the .kunitconfig is not a subset of .config. This means that we can use other tools (For example: make menuconfig) to adjust other config options. The build dir needs to be set for make menuconfig to work, therefore by default use make O=.kunit menuconfig.

Configuring, building, and running tests

If we want to make manual changes to the KUnit build process, we can run part of the KUnit build process independently. When running kunit_tool, from a .kunitconfig, we can generate a .config by using the config argument:

./tools/testing/kunit/ config

To build a KUnit kernel from the current .config, we can use the build argument:

./tools/testing/kunit/ build

If we already have built UML kernel with built-in KUnit tests, we can run the kernel, and display the test results with the exec argument:

./tools/testing/kunit/ exec

The run command discussed in section: Running tests with kunit_tool, is equivalent to running the above three commands in sequence.

Parsing test results

KUnit tests output displays results in TAP (Test Anything Protocol) format. When running tests, kunit_tool parses this output and prints a summary. To see the raw test results in TAP format, we can pass the --raw_output argument:

./tools/testing/kunit/ run --raw_output

If we have KUnit results in the raw TAP format, we can parse them and print the human-readable summary with the parse command for kunit_tool. This accepts a filename for an argument, or will read from standard input.

# Reading from a file
./tools/testing/kunit/ parse /var/log/dmesg
# Reading from stdin
dmesg | ./tools/testing/kunit/ parse

Filtering tests

By passing a bash style glob filter to the exec or run commands, we can run a subset of the tests built into a kernel . For example: if we only want to run KUnit resource tests, use:

./tools/testing/kunit/ run 'kunit-resource*'

This uses the standard glob format with wildcard characters.

Running tests on QEMU

kunit_tool supports running tests on qemu as well as via UML. To run tests on qemu, by default it requires two flags:

  • --arch: Selects a configs collection (Kconfig, qemu config options and so on), that allow KUnit tests to be run on the specified architecture in a minimal way. The architecture argument is same as the option name passed to the ARCH variable used by Kbuild. Not all architectures currently support this flag, but we can use --qemu_config to handle it. If um is passed (or this flag is ignored), the tests will run via UML. Non-UML architectures, for example: i386, x86_64, arm and so on; run on qemu.

  • --cross_compile: Specifies the Kbuild toolchain. It passes the same argument as passed to the CROSS_COMPILE variable used by Kbuild. As a reminder, this will be the prefix for the toolchain binaries such as GCC. For example:

    • sparc64-linux-gnu if we have the sparc toolchain installed on our system.

    • $HOME/toolchains/microblaze/gcc-9.2.0-nolibc/microblaze-linux/bin/microblaze-linux if we have downloaded the microblaze toolchain from the 0-day website to a directory in our home directory called toolchains.

This means that for most architectures, running under qemu is as simple as:

./tools/testing/kunit/ run --arch=x86_64

When cross-compiling, we’ll likely need to specify a different toolchain, for example:

./tools/testing/kunit/ run \
        --arch=s390 \

If we want to run KUnit tests on an architecture not supported by the --arch flag, or want to run KUnit tests on qemu using a non-default configuration; then we can write our own``QemuConfig``. These QemuConfigs are written in Python. They have an import line from..qemu_config import QemuArchParams at the top of the file. The file must contain a variable called QEMU_ARCH that has an instance of QemuArchParams assigned to it. See example in: tools/testing/kunit/qemu_configs/

Once we have a QemuConfig, we can pass it into kunit_tool, using the --qemu_config flag. When used, this flag replaces the --arch flag. For example: using tools/testing/kunit/qemu_configs/, the invocation appear as

./tools/testing/kunit/ run \
        --timeout=60 \
        --jobs=12 \

Running command-line arguments

kunit_tool has a number of other command-line arguments which can be useful for our test environment. Below are the most commonly used command line arguments:

  • --help: Lists all available options. To list common options, place --help before the command. To list options specific to that command, place --help after the command.


    Different commands (config, build, run, etc) have different supported options.

  • --build_dir: Specifies kunit_tool build directory. It includes the .kunitconfig, .config files and compiled kernel.

  • --make_options: Specifies additional options to pass to make, when compiling a kernel (using build or run commands). For example: to enable compiler warnings, we can pass --make_options W=1.

  • --alltests: Enable a predefined set of options in order to build as many tests as possible.


    The list of enabled options can be found in tools/testing/kunit/configs/all_tests.config.

    If you only want to enable all tests with otherwise satisfied dependencies, instead add CONFIG_KUNIT_ALL_TESTS=y to your .kunitconfig.

  • --kunitconfig: Specifies the path or the directory of the .kunitconfig file. For example:

    • lib/kunit/.kunitconfig can be the path of the file.

    • lib/kunit can be the directory in which the file is located.

    This file is used to build and run with a predefined set of tests and their dependencies. For example, to run tests for a given subsystem.

  • --kconfig_add: Specifies additional configuration options to be appended to the .kunitconfig file. For example:

    ./tools/testing/kunit/ run --kconfig_add CONFIG_KASAN=y
  • --arch: Runs tests on the specified architecture. The architecture argument is same as the Kbuild ARCH environment variable. For example, i386, x86_64, arm, um, etc. Non-UML architectures run on qemu. Default is um.

  • --cross_compile: Specifies the Kbuild toolchain. It passes the same argument as passed to the CROSS_COMPILE variable used by Kbuild. This will be the prefix for the toolchain binaries such as GCC. For example:

    • sparc64-linux-gnu- if we have the sparc toolchain installed on our system.

    • $HOME/toolchains/microblaze/gcc-9.2.0-nolibc/microblaze-linux/bin/microblaze-linux if we have downloaded the microblaze toolchain from the 0-day website to a specified path in our home directory called toolchains.

  • --qemu_config: Specifies the path to a file containing a custom qemu architecture definition. This should be a python file containing a QemuArchParams object.

  • --qemu_args: Specifies additional qemu arguments, for example, -smp 8.

  • --jobs: Specifies the number of jobs (commands) to run simultaneously. By default, this is set to the number of cores on your system.

  • --timeout: Specifies the maximum number of seconds allowed for all tests to run. This does not include the time taken to build the tests.

  • --kernel_args: Specifies additional kernel command-line arguments. May be repeated.

  • --run_isolated: If set, boots the kernel for each individual suite/test. This is useful for debugging a non-hermetic test, one that might pass/fail based on what ran before it.

  • --raw_output: If set, generates unformatted output from kernel. Possible options are:

    • all: To view the full kernel output, use --raw_output=all.

    • kunit: This is the default option and filters to KUnit output. Use --raw_output or --raw_output=kunit.

  • --json: If set, stores the test results in a JSON format and prints to stdout or saves to a file if a filename is specified.

  • --filter: Specifies filters on test attributes, for example, speed!=slow. Multiple filters can be used by wrapping input in quotes and separating filters by commas. Example: --filter "speed>slow, module=example".

  • --filter_action: If set to skip, filtered tests will be shown as skipped in the output rather than showing no output.

  • --list_tests: If set, lists all tests that will be run.

  • --list_tests_attr: If set, lists all tests that will be run and all of their attributes.