Hi all - I am learning about Linux and want to see if my understanding is correct on this - the list of major parts of any distro:
- the Linux Kernel
- GRUB or another bootloader
- one or more file systems (gotta work with files somehow, right?)
- one or more Shells (the terminal - bash, zsh, etc…)
- a Desktop Environment (the GUI, if included, like KDE or Gnome - does this include X11 or Wayland or are those separate from the DE?)
- a bunch of Default applications and daemons (is this where systemd fits int? I know about the GNU tools, SAMBA, CUPS, etc…)
- a Package Manager (apt, pacman, etc…)
Am I forgetting anything at this 50,000 foot level? I know there are lots of other things we can add, but what are the most important things that ALL Linux distributions include?
Thanks!
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I would say, that from most important to least important components are:
- kernel
- init system (systemd, openrc, runit…)
- C library (glibc, musl)
- filesystem
- coreutils
- shell
- bootloader
- package manager
- x11/Wayland (if any)
- sound system (if any)
- WM (if any)
- DE (if any)
what do u mean by important? like ‘essential to the system’, or ‘important to consider when choosing a distro’, or what?
I mean “something out of ordinary about it affects your experience with this distro the most”.
i see
I’m surprised you put shell so high when it tends to be less impactful in my experience. Like I care a lot more if my distro is using GNOME instead of KDE a lot more than if it’s using bash instead of zsh. Plus it’s easy to install and use a different shell
It is easy to install another shell indeed, but it is quite difficult to configure it. While installation of DE is usually done with just one command. And you can use linux without DE, but not without shell. Many distributions even do not install DE by default at all.
Okay but unless you are spending a lot of time in the command line, one (POSIX compliant) shell is as good as another. Like yes every distro needs a shell, but I don’t much care which shell it is.
One thing I don’t know: if C is a compiled language already, what exactly does the C library do?
it is a dynamically linked library, meaning its not in the compiled binary, but its assumed to already be on the system. as opposed to a statically linked binary. this lowers the file size of the binaries, because most will use the standard library.
edit: this may not be 100% correct, but its the general idea
Most C binaries usually do not contain everything needed for their execution. It would make them too platform-specific. What most c programs do is that they use standard c library from platform for low-level things and communication with the system like memory allocation or stdin/stdout things, for example.
Wouldn’t the c library be more important than the init system?
You are probably right. It is probably even more important than kernel.
Not really.
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I think you would also need an initial run process such as systemd or the sysV runlevels.
Fun fact, the init process can be anything, even /bin/bash or a shell script. But if it ends or dies so does the system, and of course you want extra features like multiuser capability, better interface etc. So it’s typically a more complex system like you said, that starts a bunch of other things. But you can still see the init process with PID 1 there in the process list. 😊
Fun fact: On Slackware, the init process is just a shell script (which launches other shell scripts).
The logo.
Also:
- init system, without which you’d be left with only one program running at a time
- some programs are written in interpreted language (e.g python, shell, perl), so the interpreter would also be required
- C library, without which none of the above would function (yes, even if all the programs are statically compiled, it still has that library included with each executable)
- this one is not necessary for the runtime, but is needed for creating a working system: toolchain – preprocessor, compiler, linker, assembler – all the stuff for transforming the source code into executables
Another comment mentioned Linux From Scratch, I’d totally recommend that, but it would take so much of your time manually building stuff (which is why it is so educational). If you don’t have the time, you may want to opt with Gentoo instead.
I would also mention:
- The multi-user system, which is a bunch of config files, libraries, utils and UIs, that deal with logging in or doing stuff as a specific user.
- The logging system. Individual applications can simply log to a different file each but for system services the logging is usually centralized and offers additional features (like logging remotely etc.)
- Setting up networking is pretty much mandatory these days.
You pretty much got it, except for the fifth point.
A desktop environment (“DE”) is separate from the compositor (X11 or Wayland), but can’t exist without it.
At the end of the day, a DE is really just a “window manager” with a bunch of bundled applications, like taskbars/panels, a file manager, an app menu, etc. It’s as minimal or as feature rich as you want it to be.
The window manager dictates what to draw on the screen and where, but the compositor is what actually does the work. One is kind of useless without the other.
Hopefully that makes sense, I’m not a rocket surgeon.
The major parts of any distro are just bootloader, kernel, init, shell, and package system. The filesystem isn’t “part” of the distro, it’s just an abstraction layer to work with data on the drive, and should be considered independent of the packaged distribution itself.
With the above, you can run the basics of Linux on a device. The DE is not needed, and included packages and libraries are at the discretion of the maintainers. The included choices of all the above is the only thing that differentiates each distro.
If it helps in your understanding at all, back in the day, in order to install something like Slackware, you had to build each layer of these things manually like so: format and partition disk from disk in DOS, copy bootloader to newly partitioned HDD, boot to single user mode, compile kernel, add entries to bootloader, reboot from disk to Linux kernel, open TTY, set user and shell, reboot again, compile DE, set init level and basic services, reboot to DE, and then you had a Desktop.
Systemd has gone way and beyond what was supposed to be a replacement for init.rc.
Most important thing… not ALL Linux distros include systemd as the default init system. That’s the beauty of Linux (and POSIX in general), you can choose.
A biggie you miss is the toolchain: the compiler/binutils/linux-headers/libc/libstdc++ combination. The libc and usually libstdc++ are key components of any install. The other parts usually don’t make it to non-dev-desktops, but the distro couldn’t be made without them, so they’re virtually always available as packages.
Only exception is if the entire distro is cross-compiled or it’s made exclusively for containers, but those kinds of special distros break every rule imaginable anyway. Some might not even ship a bootloader or a Linux kernel by themselves.
The list is generally correct but these days, systemd has made quite an impact also. If a distribution uses systemd, it has one software to handle everything from booting (instead of grub), handling start and status of all system services etc. Its probably the largest change to the Linux ecosystem in a long time.
X11 and Wayland are desktop protocols, so things like desktop environments and window managers depends on one or them to be installed. Without them, you don’t get any graphics except for the console. It’s all built on top of one of those.
It’s easier to think about Linux on the context of what an individual application needs to run. Pretty much everything you do will have these components.
- configuration
- an executable
- a communication mechanism (dbus, networking, web server, etc)
- something that decides if the application runs or not (systemd, monit, docker/docker compose, kubernetes scheduler, or you as the user)
- a way of accepting input (keyboard and mouse, web requests, database queries, etc)
- a way of delivering an output (logging to unique log files, through syslog, or to stdout/stderr, showing something on a screen, playing a sound, returning a message to the client, etc)
- storage (optional)
- some cpu and memory capacity
That’s really it. If something isn’t working, it’s pretty much exclusively going to fall into one of those categories. What that means is going to vary significantly from app to app but understanding this is how literally everything works makes the troubleshooting process a lot easier.
Systemd.
I don’t know how helpful it is to split stuff out like that. Especially grouping so many things under “default applications and daemons”, which is most of what a desktop distro is. Also depends largely on a PC vs server setup.
should list an init system as its own bullet, which others have mentioned.
“one or more shells” doesn’t mean that much. Yes, every distro includes one but the only difference between a terminal and any other application is that a terminal needs to be able to escalate to root privileges. You can think of it as just another default (but special) application. A lot of stuff that people think about when they think of Linux distros is just various clever mechanisms for supporting the terminal shell. Like the PATH environment variable. If you are using actual desktop applications other than a terminal, there isn’t any interaction with the terminal shell application.
There’s also fwupd, for updating firmware (your hardware is gonna be running out of date/buggy/insecure code if you don’t have this).
The dbus daemon falls under the “daemons” bullet but it’s pretty important, like wayland/x11 it’s another IPC mechanism you need for programs to work correctly.
There’s also the sound system. PipeWire is the modern one that implements the interfaces of various other sound systems so existing applications work with it. https://pipewire.org/ (PipeWire also has its own IPC protocol like dbus/wayland/x11).
flatpak, snap, distrobox, toolbox, docker, podman, etc. for running sandboxed PC/server applications. I assume there are some programs that are flatpak-only these days.
gsettings/dconf for Windows-registry like config that many programs use.
There’s also plugging in an implementation of the glibc Name Service Switch, which allows libc to use a mechanism other than /etc/passwd and related files for user accounts, internet service names, DNS resolution, etc. . systemd can provide NSS implementations using its own user account mechanism.
Package management is optional according to Slackware and Linux From Scratch.
A key part you left out is the init scripts. Without those you don’t have the fundamental under the hood flavor of a distribution.
You need the “Userland” programs. Basic things like
ls,cp,cat, etc. Usually it’s GNU core tools, but there’s also BusyBox or BSD equivalents.Honestly, I wouldn’t worry too much about how the OS works. If you’re very ambitious, you could try to install Arch in a virtual machine environment: https://wiki.archlinux.org/title/Installation_guide
Installing Arch for the first time taught me a lot about how my system works, since you have to choose all the parts that make up your system yourself.
