Last month, I introduced the various TCP congestion control algorithms your Linux kernel knows about. I also mentioned a method, using the kernel module tcpprobe, that allows for measuring the parameters of live TCP connections. Unfortunately, this module requires the presence of a debugging option in the kernel called kprobes. By enabling this, you can dynamically break into any kernel routine and collect debugging and performance information non-disruptively. This sounded good on first impression - but I decided that I don't wish to introduce kprobes on every machine I have; it's better to run less code on servers. Besides, it is not a good idea to run debugging code in kernels that shouldn't be used for debugging. I had to look for other mechanisms. After rediscovering the man pages on my GNU/Linux workstation at home, I found what I was looking for: getsockopt()