A few weeks ago I was debugging network code, and I needed to check if some
sockets were bound with SO_REUSEADDR and/or SO_REUSEPORT. I researched how
I could inspect that, and was surprised to find out that the Linux kernel did
not expose those options to userland.
Thankfully, there is
a kernel module called knetstat
which lets you do this very easily by adding new files into procfs. When I
found it it only supported TCP, but I needed the information for UDP as well so
I contributed the code to
support it.
If you write networking code on Linux or just run servers, I encourage you to
check it out. It is a nice little tool that can come very handy in some
situations, including when you need to check options like SO_{RCV,SND}BUF.