As long as the comment is useful and contributes, I think it's fair game. This definitely qualifies. That said, if it's not free, I personally would prefer that be mentioned, (and at the same time a link to a free sample chapter or equivalent if it exists would be useful).
Re:Tmux 2.0 released
by hans_mueller on Thursday May 07, 2015 @01:37PM
(#9506832)
90% of HackerNews is self plug ... so don't worry :)
It was quite a good book! It might be due for an update, what with tmux plugins and other new tools. I'd buy an updated version.
http://gettingstartedwithtmux.com
(Sorry if the self plug is not cool, I'm happy to delete this comment if it's not ok but I figure the community may get use out of my work)