proc

man proc

Open Files

Helpful for troubleshooting what files are opened by a process, you can open file descriptors in ls /proc/PID/fd. It also tells you where stdin/stdout/stderr are going.

I generally use strace instead but this can be useful too.

Environment Variables

You can see environment variables for processes via cat /proc/PID/environ.

The output is null-terminated, so cat /proc/PID/environ | tr '\0' '\n' will give you more meaningful output.

This can be used to search all processes for specific variables, etc.

Executable

You can find the executable path for a process via ls -la /proc/PID/exe.