docker-library / docker-library/python
Debbuging a `-slim` image?
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Description
We are hitting a rare deadlock in production that can't be reproduced using debug images.
Only way to debug it is to attach to the production image as the problem happens.
Problem is that production are based on the -slim images.
apt install gdb and python3-dbg is not enough because the python running is built from source and not aligned with what is available in apt.
I've tried to start the corresponding non-slim image but their binaries don't seem to align enough to make gdb happy:
Start python inside -slim image
➡️ My end goal is to run gdb py-bt on this process:
docker run -ti python:3.11-slim-bookworm python3 -c "import time; time.sleep(1000)"
Inside this image there is no chance to debug at all due to missing gdb and debug symbols. This is expected.
Build a debugger image from the corresponding non-slim image.
FROM python:3.11-bookworm
RUN --mount=type=cache,target=/var/cache/apt --mount=type=cache,target=/var/lib/apt \
apt update -y && \
apt install -y gdb
docker build -t mydebugpython .
Use the newly built debug image to attach into the first running container
Find the container id and use that to attach to the same pid-namespace.
docker run \
--cap-add SYS_PTRACE \
--pid container:15aab7ea5f57 \
--privileged \
-ti \
--entrypoint bash docker.io/library/mydebugpython
root@bb90d04f8722:/# gdb -q python --pid 1 -ex "py-bt"
Reading symbols from python...
Attaching to program: /usr/local/bin/python, process 1
warning: Build ID mismatch between current exec-file /usr/local/bin/python
and automatically determined exec-file /usr/local/bin/python3.11
exec-file-mismatch handling is currently "ask"
Load new symbol table from "/usr/local/bin/python3.11"? (y or n) y
Reading symbols from /usr/local/bin/python3.11...
Reading symbols from target:/usr/local/bin/../lib/libpython3.11.so.1.0...
(No debugging symbols found in target:/usr/local/bin/../lib/libpython3.11.so.1.0)
Reading symbols from target:/lib/x86_64-linux-gnu/libc.so.6...
Reading symbols from /usr/lib/debug/.build-id/82/ce4e6e4ef08fa58a3535f7437bd3e592db5ac0.debug...
Reading symbols from target:/lib/x86_64-linux-gnu/libm.so.6...
Reading symbols from /usr/lib/debug/.build-id/ea/87e1b3daf095cd53f1f99ab34a88827eccce80.debug...
Reading symbols from target:/lib64/ld-linux-x86-64.so.2...
Reading symbols from /usr/lib/debug/.build-id/38/e7d4a67acf053c794b3b8094e6900b5163f37d.debug...
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
__GI___clock_nanosleep (clock_id=1, flags=1, req=0x7ffd9d9ec458, rem=0x0) at ../sysdeps/unix/sysv/linux/clock_nanosleep.c:71
71 ../sysdeps/unix/sysv/linux/clock_nanosleep.c: No such file or directory.
Traceback (most recent call first):
(unable to read python frame information) # <-------------- :(
So it seems like the difference of slim and non-slim isn't only the presence of debug symbols or not, but also the binary is built differently?
Is this possible to solve somehow? My knowledge of how python is built and how to operate gdb are only moderate.
Contributor guide
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First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
No repository file or test is named. Start by comparing the python:3.11-slim-bookworm and python:3.11-bookworm image builds, then reproduce the gdb attach commands and inspect the executable and debug-symbol mismatch. Done means establishing whether py-bt can work against the slim image and documenting a reproducible debugging approach or limitation.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- docker, python
- Domain
- devops, tooling
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 25/100