docs: Add debug.md

docs/debug.md

@@ -0,0 +1,60 @@
+---
+parent: Contributing
+nav_order: 1
+---
+
+# Debugging rpm-ostree
+{: .no_toc }
+
+1. TOC
+{:toc}
+
+
+## Setting verbose debug messages when using the CLI.
+
+The rpm-ostree and ostree code uses gtk's glib for the as a C library. An advantage to using glib is that to enable verbose debug messages we just need to set an environment variable:
+[G_MESSAGES_DEBUG=all](https://docs.gtk.org/glib/logging.html#debug-message-output). 
+
+Additionally, part of rpm-ostree code is written in Rust to enable verbose logs on the Rust code the environment variable is:
+[RUST_LOG=debug](https://docs.rs/env_logger/latest/env_logger/).
+
+An example of how to set use the environment variables is:
+
+```
+env G_MESSAGES_DEBUG=all RUST_LOG=debug rpm-ostree status
+```
+
+Since ostree is called from rpm-ostree it will output ostree debug messages too.
+
+## Enabling verbose debug messages when not using the CLI.
+
+If you need output from rpm-ostreed.service, another client such as Zincati or ostree-finalize-staged.service
+you might need to override the environment variables for those services.
+
+A way to do this is using the `systemctl edit` command.
+
+For example:
+
+```
+systemctl edit rpm-ostreed
+```
+or
+```
+systemctl edit zincati.service
+```
+
+Then adding:
+```
+[Service]
+Environment="G_MESSAGES_DEBUG=all"
+```
+
+and restarting the service.
+
+After that a more verbose output should be seen in the journal:
+
+```
+journalctl -b -u rpm-ostreed
+```
+
+**Please Note** depending on what are you trying to debug you might need to override the environment for different services.