History
1990
We can consider Linus Torvalds’s email on August 25, 1991, to the comp.os.minix newsgroup as the birth of the Linux project, at least in terms of the public record. This hobby project soon took off, both in terms of lines of code (LOC) and in terms of adoption. For example, after less than three years, Linux 1.0.0 was released with over 176,000 LOCs. By that time, the original goal of being able to run most Unix/GNU software was already well reached. Also, the first commercial offering appeared in the 1990s: Red Hat Linux.
2000 to 2010
Linux was a teenager, and it was increasingly used by Google, Amazon, IBM, etc. distro wars started
2010 to now
Linux establish itself as the workhorse for data centers, cloud, iot, phones.
Why use an OS at all?
Technically speaking, an OS is not strictly needed. There are systems out there that do not have an OS. These are usually embedded systems with a tiny footprint: think of an IoT beacon. They simply do not have the resources available to keep anything else around other than one application. For example, with Rust you can use its Core and Standard Library to run any app on bare metal
However, you would end up taking care of many low-level hardware concerns such as:
- dealing with interrupts
- memory management
- I/O
- networking
- files management
Instead, OS provides a nice abstraction that is exposed via an API which we refer to system calls. Programming languages are built on top of syscalls, potentially wrap them in library
Example syscal
at the Linux syscall getuid(2):
getuid() returns the real user ID of the calling process.
Sections in man
The (2) in getuid(2) is a terminology that the man utility (think built-in help pages) uses to indicate the section of the command assigned in man, akin to a postal or country code.
From the CLI, we would invoke the getuid syscall using the id command like so: id --user
Linux Distributions
A distribution is the Linux Kernel bundled with related components such as:
- package management
- file system layout
- init system
- shell
- other preselected software
See Linux Distributions for the full breakdown of bases, family trees, release models, init systems, and desktop environments.
Building your own distros
Most people tried and abandoned this road, but if you want, you can try Arch Linux
Distrowatch allows to get a glimpse on the incredible number of Linux distributions available
Resource visibility
Linux historically had a global view on resource, such as CPU, ram, files, processes, networking. With containers this is change, as containers can have restricted access to resources.
Tip
Not all resources in Linux are represented to through a file, although there are systems such as Plan 9 from Bell Labs takes this much further
cat /proc/version
cat /proc/cpuinfo | grep "model name"
cat /proc/$$/status