drgn
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.. 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.
Additionally, drgn is designed as a library that can be used to build debugging
and introspection tools; see the official tools <https://github.com/osandov/drgn/tree/main/tools>
_.
drgn was developed at Meta <https://opensource.fb.com/>
_ for debugging the
Linux kernel (as an alternative to the crash <https://crash-utility.github.io/>
_ 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>
_.
.. start-installation
Installation
Package Manager
^^^^^^^^^^^^^^^
drgn can be installed using the package manager on some Linux distributions.
.. image:: https://repology.org/badge/vertical-allrepos/drgn.svg
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:alt: Packaging Status
-
Fedora >= 32
.. code-block:: console
$ sudo dnf install drgn
-
RHEL/CentOS >= 8
Enable EPEL <https://docs.fedoraproject.org/en-US/epel/#_quickstart>
_. Then:
.. code-block:: console
$ sudo dnf install drgn
-
Arch Linux
Install the drgn <https://aur.archlinux.org/packages/drgn/>
_ package from
the AUR <https://wiki.archlinux.org/title/Arch_User_Repository>
_.
-
Debian >= 12 (Bookworm)
.. code-block:: console
$ sudo apt install python3-drgn
-
Gentoo
.. code-block:: console
$ sudo emerge dev-debug/drgn
-
openSUSE
.. code-block:: console
$ sudo zypper install python3-drgn
-
Ubuntu
Enable the michel-slm/kernel-utils PPA <https://launchpad.net/~michel-slm/+archive/ubuntu/kernel-utils>
_.
Then:
.. code-block:: console
$ sudo apt install python3-drgn
pip
^^^
If your Linux distribution doesn't package the latest release of drgn, you can
install it with pip <https://pip.pypa.io/>
_.
First, install pip <https://packaging.python.org/guides/installing-using-linux-tools/#installing-pip-setuptools-wheel-with-linux-package-managers>
_.
Then, run:
.. code-block:: console
$ sudo pip3 install drgn
This will install a binary wheel by default. If you get a build error, then pip
wasn't able to use the binary wheel. Install the dependencies listed below <#from-source>
_ and try again.
Note that RHEL/CentOS 6, Debian Stretch, Ubuntu Trusty, and Ubuntu Xenial (and
older) ship Python versions which are too old. Python 3.6 or newer must be
installed.
From Source
^^^^^^^^^^^
To get the development version of drgn, you will need to build it from source.
First, install dependencies:
-
Fedora
.. code-block:: console
$ sudo dnf install autoconf automake check-devel elfutils-devel gcc git libkdumpfile-devel libtool make pkgconf python3 python3-devel python3-pip python3-setuptools
-
RHEL/CentOS
.. code-block:: console
$ sudo dnf install autoconf automake check-devel elfutils-devel gcc git libtool make pkgconf python3 python3-devel python3-pip python3-setuptools
Optionally, install libkdumpfile-devel
from EPEL on RHEL/CentOS >= 8 or
install libkdumpfile <https://github.com/ptesarik/libkdumpfile>
_ from
source if you want support for the makedumpfile format.
Replace dnf
with yum
for RHEL/CentOS < 8.
-
Debian/Ubuntu
.. code-block:: console
$ sudo apt install autoconf automake check gcc git liblzma-dev libelf-dev libdw-dev libtool make pkgconf python3 python3-dev python3-pip python3-setuptools zlib1g-dev
Optionally, install libkdumpfile from source if you want support for the
makedumpfile format.
-
Arch Linux
.. code-block:: console
$ sudo pacman -S --needed autoconf automake check gcc git libelf libtool make pkgconf python python-pip python-setuptools
Optionally, install libkdumpfile <https://aur.archlinux.org/packages/libkdumpfile/>
__ from the AUR or from
source if you want support for the makedumpfile format.
-
Gentoo
.. code-block:: console
$ sudo emerge --noreplace --oneshot dev-build/autoconf dev-build/automake dev-libs/check dev-libs/elfutils sys-devel/gcc dev-vcs/git dev-libs/libkdumpfile dev-build/libtool dev-build/make dev-python/pip virtual/pkgconfig dev-lang/python dev-python/setuptools
-
openSUSE
.. code-block:: console
$ sudo zypper install autoconf automake check-devel gcc git libdw-devel libelf-devel libkdumpfile-devel libtool make pkgconf python3 python3-devel python3-pip python3-setuptools
Then, run:
.. code-block:: console
$ git clone https://github.com/osandov/drgn.git
$ cd drgn
$ python3 setup.py build
$ sudo python3 setup.py install
.. end-installation
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
. Make sure to
install debugging symbols <https://drgn.readthedocs.io/en/latest/getting_debugging_symbols.html>
_ for
whatever you are debugging.
Then, you can access variables in the program with prog['name']
and access
structure members with .
:
.. code-block:: pycon
$ sudo drgn
>>> prog['init_task'].comm
(char [16])"swapper/0"
You can use various predefined helpers:
.. code-block:: pycon
>>> len(list(bpf_prog_for_each()))
11
>>> task = find_task(115)
>>> cmdline(task)
[b'findmnt', b'-p']
You can get stack traces with stack_trace()
and access parameters or local
variables with trace['name']
:
.. code-block:: pycon
>>> trace = stack_trace(task)
>>> trace[5]
#5 at 0xffffffff8a5a32d0 (do_sys_poll+0x400/0x578) in do_poll at ./fs/select.c:961:8 (inlined)
>>> poll_list = trace[5]['list']
>>> file = fget(task, poll_list.entries[0].fd)
>>> d_path(file.f_path.address_of_())
b'/proc/115/mountinfo'
.. end-quick-start
See the user guide <https://drgn.readthedocs.io/en/latest/user_guide.html>
_
for more details and features.
.. start-for-index
Getting Help
- The
GitHub issue tracker <https://github.com/osandov/drgn/issues>
_ is the
preferred method to report issues. - There is also a
Linux Kernel Debuggers Matrix room <https://matrix.to/#/#linux-debuggers:matrix.org>
_.
License
Copyright (c) Meta Platforms, Inc. and affiliates.
drgn is licensed under the LGPLv2.1 <https://www.gnu.org/licenses/old-licenses/lgpl-2.1.en.html>
_ or later.
.. end-for-index