I'm not claiming any C ability myself, but in addition to things which have already been mentioned: the old Steve Summit comp.lang.c C FAQ http://c-faq.com/ was only updated up to 2005 but is still hard to ignore.

For the Linux C interface there's https://nostarch.com/tlpi and http://www.apuebook.com/apue3e.html / http://www.unpbook.com/ , all old to different degrees. http://www.danlj.org/lad/ was great but even the second edition http://www.worldcat.org/title/linux-application-development-... is probably out of date by now. ( https://9p.io/cm/cs/upe/index.html is most certainly out of date, but more than that it's almost an anti-C-interface book by comparison to the C-API-centric view of Unix which has become prevalent since, in some part due to the popularity of K&R... https://www.cs.princeton.edu/~bwk/tpop.webpage/ and http://www.catb.org/esr/writings/taoup/ are in the same "anti-C-book" vein.)