Shadow works by intercepting system calls and reimplementing them in a simulated environment. So far the Shadow dev team has focused on getting the syscalls used by Tor working well, but your application may be using unsupported syscalls and/or some unsupported aspects of the currently supported syscalls.

There are two ways to get some hints about what could be failing when running your app in Shadow:

• If your app is using unsupported syscalls, Shadow will log a warning in the shadow.log file (format explained here) that contains the following string: "Detected unsupported syscall”…
• We just merged a new shadow cli option that will tell shadow to log strace-style information to each virtual host’s directory (shadow.data/hosts/<name>/)“ - turn it on with —use-strace-logging true, run your sim, and check the logs in the hosts data directories

Feel free to open a discussion if you notice some missing system calls that you think are important to add!