drgn
====

.. image:: https://img.shields.io/pypi/v/drgn
    :target: https://pypi.org/project/drgn/
    :alt: PyPI

.. image:: https://github.com/osandov/drgn/workflows/CI/badge.svg
    :target: https://github.com/osandov/drgn/actions
    :alt: CI Status

.. image:: https://readthedocs.org/projects/drgn/badge/?version=latest
    :target: https://drgn.readthedocs.io/en/latest/?badge=latest
    :alt: Documentation Status

.. image:: https://img.shields.io/badge/code%20style-black-000000.svg
    :target: https://github.com/psf/black

.. start-introduction

drgn (pronounced "dragon") is a debugger with an emphasis on programmability.
drgn exposes the types and variables in a program for easy, expressive
scripting in Python. For example, you can debug the Linux kernel:

.. code-block:: pycon

    >>> from drgn.helpers.linux import list_for_each_entry
    >>> for mod in list_for_each_entry('struct module',
    ...                                prog['modules'].address_of_(),
    ...                                'list'):
    ...    if mod.refcnt.counter > 10:
    ...        print(mod.name)
    ...
    (char [56])"snd"
    (char [56])"evdev"
    (char [56])"i915"

Although other debuggers like `GDB <https://www.gnu.org/software/gdb/>`_ have
scripting support, drgn aims to make scripting as natural as possible so that
debugging feels like coding. This makes it well-suited for introspecting the
complex, inter-connected state in large programs. It is also designed as a
library that can be used to build debugging and introspection tools; see the
official `tools <https://github.com/osandov/drgn/tree/master/tools>`_.

drgn was developed for debugging the Linux kernel (as an alternative to the
`crash <http://people.redhat.com/anderson/>`_ utility), but it can also debug
userspace programs written in C. C++ support is in progress.

.. end-introduction

Documentation can be found at `drgn.readthedocs.io
<https://drgn.readthedocs.io>`_.

Installation
------------

.. start-install-dependencies

Install dependencies:

Arch Linux:

.. code-block:: console

    $ sudo pacman -S --needed autoconf automake gawk gcc libelf libtool make pkgconf python python-setuptools

Debian/Ubuntu:

.. code-block:: console

    $ sudo apt-get install autoconf automake gawk gcc libelf-dev libdw-dev libtool make pkgconf python3 python3-dev python3-setuptools

Note that Debian Stretch, Ubuntu Trusty, and Ubuntu Xenial (and older) ship
Python and elfutils versions which are too old. Python 3.6 and elfutils 0.170
or newer must be installed manually.

Fedora:

.. code-block:: console

    $ sudo dnf install autoconf automake elfutils-devel gawk gcc libtool make pkgconf python3 python3-devel python3-setuptools

Optionally, install:

* `libkdumpfile <https://github.com/ptesarik/libkdumpfile>`_ if you want
  support for kdump-compressed kernel core dumps

.. end-install-dependencies

Then, run:

.. code-block:: console

    $ sudo pip3 install drgn

See the `installation documentation
<https://drgn.readthedocs.io/en/latest/installation.html>`_ for more options.

Quick Start
-----------

.. start-quick-start

drgn debugs the running kernel by default; run ``sudo drgn``. To debug a
running program, run ``sudo drgn -p $PID``. To debug a core dump (either a
kernel vmcore or a userspace core dump), run ``drgn -c $PATH``. The program
must have debugging symbols available.

Then, you can access variables in the program with ``prog['name']``, access
structure members with ``.``, use various predefined helpers, and more:

.. code-block:: pycon

    $ sudo drgn
    >>> prog['init_task'].comm
    (char [16])"swapper/0"
    >>> d_path(fget(find_task(prog, 1), 0).f_path.address_of_())
    b'/dev/null'
    >>> max(task.stime for task in for_each_task(prog))
    (u64)4192109975952
    >>> sum(disk.gendisk.part0.nr_sects for disk in for_each_disk(prog))
    (sector_t)999705952

.. end-quick-start

See the `user guide <https://drgn.readthedocs.io/en/latest/user_guide.html>`_
for more information.

License
-------

.. start-license

Copyright (c) Facebook, Inc. and its affiliates.

drgn is licensed under the `GPLv3
<https://www.gnu.org/licenses/gpl-3.0.en.html>`_ or later.

.. end-license