Version 2.0 of the book is still free (Creative-Commons) and can be downloaded book in PDF format. 

In addition to the correction of minor typos, this version includes advanced sections on the terminal, mmu, gather/scatter, asynchronous I/O, exercises and some minor additions (sudo, etc).

Authors' review: "This is a book on operating systems, focused on GNU/Linux systems. We started writing it during the first confinement caused by the COVID-19 pandemic, as part of the online material to support our Telematics/Telecommunications Engineering and Engineering students. Robotics Software As such, it is an eminently practical book (using the C programming language), although there are chapters that include more theoretical concepts.

The content focuses on an introduction to Unix-like systems, the basic structure of the system (history, kernel, user area, basic use, etc.), the effective use of the shell (basic commands, creation of shell scripts, pipelines, use of the terminal, regular expressions, grep, sed, awk, etc.), understanding and use of processes (system calls, scheduling, etc.), understanding of file systems and the use of files (system calls, file system format, etc.), understanding and use of memory (memory management, etc.), communication between processes (pipes, sockets, fifos, signals, etc.). ) and an introduction to concurrent programming (race conditions, shared memory, locks, threads, etc.).

The examples have been tested on Linux (specifically, an Ubuntu distribution), but in principle they should be easy to port to any Unix-like system."