It's from iproute2 - sockstat "ss" Circa ~ 2001, although it's been through a few maintainers since.
https://github.com/shemminger/iproute2/commits/master/misc/s...
Re:Linux debugging tools you'll love
by marcosdumay on Wednesday September 07, 2016 @08:22PM
(#12449211)
It's installed by default at my Debian stable computer. Yet, there is not package for it, must be at the basic tools.
Starting about when? Most of the distros I use are a couple years old, and I don't see "ss" under the package managers.