mutter/doc/debugging.md
Sebastian Wick edfd1880c9 docs: Move the gitlab wiki and other docs to the docs/ directory
Let's try to consolidate our documentation in doc/ in the repo. This
includes some documentation from README.md, the HACKING.md coding style
and the gitlab wiki.

The README.md file now links to all top-level topics (i.e. not reachable
via other topics).

This also includes a few small changes to make things more consistent.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3465>
2024-01-03 20:54:57 +00:00

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# Debugging
## Nested D-Bus session
### Installing
Download and place [dbus-session.sh](uploads/a209c8f1fe6b51df669b58bab1300199/dbus-session.sh) in `~/.local/bin/` and make it executable.
### Using
To create a nested D-Bus user session, run
```sh
dbus-session.sh -n
```
This will create a D-Bus session, and attach to it.
To attach to the same session from another terminal, run
```sh
dbus-session.sh -x
```
## Nested mutter or gnome-shell
To run a nested mutter or gnome-shell instance, i.e. when you are presented with a floating window running mutter or gnome-shell, first enter a [nested D-Bus session](#nested-d-bus-session), then pass `--nested` to either gnome-shell or mutter. E.g.
```sh
mutter --nested
```
## Headless GNOME Shell and GNOME Remote Desktop
First create [nested D-Bus session](#nested-d-bus-session). In this, run gnome-shell in headless mode with a virtual monitor. E.g.
```sh
[jonas@localhost gnome-shell]$ dbus-session.sh -n
[ D-Bus 60ff ][jonas@localhost gnome-shell]$ gnome-shell --headless --virtual-monitor 1280x720
```
```sh
[jonas@localhost gnome-remote-desktop]$ dbus-session.sh -x
[ D-Bus 60ff ][jonas@localhost gnome-remote-desktop]$ ./build/src/gnome-remote-desktop-daemon
```
## Reproducing CI test failures locally
1. Create a podman that can run gdb locally using the same image used in CI. The example below uses the tag `x86_64-2022-01-20` but this will depend on the image used by the failed CI job. The Fedora version may also differ.
```sh
podman pull registry.gitlab.gnome.org/gnome/mutter/fedora/35:x86_64-2022-01-20
podman run -t -i --cap-add=SYS_PTRACE registry.gitlab.gnome.org/gnome/mutter/fedora/35:x86_64-2022-01-20 bash -l
```
2. Clone, build and install mutter inside the container
```sh
git clone https://gitlab.gnome.org/[your-user]/mutter.git -b [merge-request-branch]
cd mutter
meson build
ninja -C build install
```
3. Install debug utilities
```sh
dnf install -y gdb
```
4. Replicate a environment and run the test inside gdb. What you need here depends on the test that needs investigation. In the simplest case, the following is enough:
```sh
export XDG_RUNTIME_DIR=$PWD/runtime-dir
mkdir -p $XDG_RUNTIME_DIR
./src/tests/meta-dbus-runner.py xvfb-run meson test -C build --setup plain --gdb failing-test-case
```
The need for `xvfb-run` depends on whether the test case uses the nested backend or the headless backend.
If it involves screen casting, it becomes a bit more complicated:
```sh
export XDG_RUNTIME_DIR=$PWD/runtime-dir
mkdir -p $XDG_RUNTIME_DIR
./src/tests/meta-dbus-runner.py bash -l
pipewire&
wireplumber&
meson test -C build --setup plain --gdb failing-test-case
```