This tool is useful for watching what a process is doing with its file descriptors. My initial use case was an Amazon AWS Glacier tool I was using to upload large files that did not give me a progress bar. I initially thought I might just modify that open source tool to give me progress, but found that it would involve substantial changes. I should be able to find information about where any process is with regard to its file descriptors... hmm...
So I created 'fdmon'. You can see that the last file descriptor listed above shows me the progress of my upload. By reading information from /proc, I am able to assemble information about which file descriptors are likely to have a useful position, and print out a display showing status over time.
All you need to have is Ruby and an operating system with a standard /proc filesystem. Simply run the program with one argument -- the process ID (PID) that you want to monitor. As long as you have permission for the indicated process.