Some of my favorites that have stayed at least pretty relevant. Disclosure: not an old timer.

- UNIX and Linux System Administration Handbook. Get the most recently volume. It's a tomb (~1200 for the most recent).

- If you do any SQL, SQY Performance Explained is an 80/20 read for DB indexes, query optimization, and troubleshooting

- A Philosophy of Software Design (more recent). Just a great book on good design considerations to keep in mind.

- Mastering Regular Expressions. The first half of the book will make you confident. The second half will show you how they're implemented. Regular expressions aren't something to be afraid of!

- Designing Data Intensive Applications (more recent). Great book about data infra design decisions. Maybe not the scope you're looking for though.

- Design Patterns (Gang of Four). Absolute classic. Hard to read all the way through though, more of a reference read. You'll recognize a lot of the patterns. You'll find some great to see a formal definition of, and you'll see some you never want to use.

- Clean Architecture - Uncle Bob's best book IMO. I really don't like Clean Code, but this book talks a lot about interfaces and the right level of separation in your systems.

- K&R, as you mentioned, is of course a classic

- The AWK Programming Language is a nice quick read with similar quality and structure to K&R.

- Beej's Guide to Network Programming. The best overview of network programming, including the C API. Plus this book is genuinely funny. Beej has a ton of great stuff, all on their website for free, or in print.

- The Rust Programming Language is very well written too. Also online for free or in print.

Is there a more in depth introduction to Linux than the book you cited?

It’s long and covers many topics, yet sometimes not in sufficient detail (see boot process).