I'm running an application from a container image, and the image includes a configuration file that is normally updated through the application's settings screen. There appears to be a bug where changing one particular field in the UI does not write the new value to the configuration file.
For troubleshooting, I want to locate the file, edit it manually inside the running container, save it, and then reload or restart the application using its built-in control. What is the best way to discover where the configuration file is stored when paths can differ between images and hosts? Also, what is the recommended way to make the change persistent instead of losing it when the container is recreated?
4 Answers
A practical workflow is: inspect the container, check its mounts and startup environment, enter it with `docker exec`, locate and examine the likely file, then use `docker diff` while reproducing the UI change. For one-off investigation you can also use `docker cp` to copy a file out of the container, but persistent configuration should be managed outside the image through a mount or volume.
Editing the file inside the running container is fine for a quick bug test, but it is not a durable fix. Changes made only to the container’s writable layer can disappear when the container is removed or recreated. Once you find the file, bind-mount that file or its configuration directory from the host, or use a named volume, and edit the persistent copy instead.
If you are trying to determine which file the application actually changed, run `docker diff ` before and after changing the setting. It lists files modified since the container started and can save you from searching the entire filesystem. Keep in mind that files stored on a mounted volume may not appear as changes in the container’s writable layer, so check the mounts with `docker inspect` too.
A mounted configuration file or directory is normally located on the host, so inspect the container’s `Mounts` information to find the host-side path.
Start by checking the image and container configuration instead of guessing paths. `docker inspect` can show the working directory, startup command, environment variables, and mounted files or directories. If necessary, open a shell with `docker exec -it sh` (or `bash` if the image includes it) and inspect the filesystem from there. The application’s documentation and environment variables are usually the most reliable way to identify its config path.
The important distinction is that a normal restart may preserve the container’s writable layer, while replacing or recreating the container generally does not. A bind mount or volume is the safer choice for configuration that must survive updates.