Does not seem to start on CentOS 7, not sure how to debug the issue

I have a fairly long thread on the dropbox community forum but no-one has replied, I'm not sure if they support the flatpak version of Dropbox, so I thought I'd post here. See my latest post at https://www.dropboxforum.com/t5/Dropbox-installs-integrations/Cannot-run-latest-dropboxd-on-Centos-7-with-glibc-2-17-and/m-p/431794/highlight/true#M94908

I have moved up from kernel 3.10 which I think caused my first problem, and all file systems on my host are ext4, yet when I try to run the flatpak app nothing seems to happen. I see no new processes with dropbox in them, and no new files are changed in my home directory.

This is from the dropboxforum.com post:

I found you can run a shell within the flatpak environment of an app, with:

```
# flatpak -y install flathub org.gnome.Sdk//3.36
# flatpak run -vvv --command=sh --devel com.dropbox.Client
```

This gives me a shell, and given that the last line of output when trying to run the flatpak app normally is:

`F: Running '/usr/libexec/flatpak-bwrap --args 25 dropbox-app'`

I looked for dropbox-app and found /app/bin/dropbox-app which is a Python script that would try to run /app/extra/.dropbox-dist/dropboxd but gives this output:

```
# ./dropbox-app --debug
INFO:root:Trying to own the dropbox dbus name...
INFO:root:Looking for Dropbox configuration...
INFO:root:Dropbox configuration not found
INFO:root:Another instance of dropbox is already running but no Dropbox folder was found; launching the daemon again
INFO:root:Trying to own the dropbox dbus name (this time replacing existing ones)...
INFO:root:Not the main launcher instance. Exiting
```

It seems to think another instance is running, however I cannot see any likely looking processes:
```
# ps -aef | grep -i dropb
root 18 2 0 05:07 ? 00:00:00 grep -i dropb
```

Looking into the dropbox-app python script, it prints that "but no Dropbox folder was found" message if the get_dropbox_directory() function fails, and here my knowledge of flatpak falls down. I can't tell if running the app from the debug shell is a good idea. Is it going to be able to access the dropbox folder in the host system's user directory? the /app filesystem is mounted readonly so I cannot hack the script to try to debug it.

Does this look like a problem to you guys? I know very little about Flatpak so am not really sure what should be happening.

Start with the linked Dropbox forum report and reproduce the flatpak run -vvv command on CentOS 7. Inspect /app/bin/dropbox-app, especially get_dropbox_directory(), and compare its behavior in the debug shell with the host process and home directory. Done means establishing whether the client is supported and identifying a reproducible cause or documenting the missing information needed for one.

Written by the indexing model from the issue text.