Mailinglist Archive: opensuse (1690 mails)

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Re: [opensuse] Basic learning tutorials query
On Wed, Nov 2, 2011 at 3:31 PM, Brian K. White <brian@xxxxxxxxx> wrote:

rpm and deb are merely packaged software management systems.
There are many ways to manage software installation and removal, and these
two are by far the most common, but by no means the only ways.
They are only the most common because debian and redhat, and their spin-offs
like centos and ubuntu, happen to be the most popular linux distributions
currently.

Technically .apk is probably the most popular linux software package fomat
since there are probably more Android devices in use than linux desktops
even though redhat and debian have been around a lot longer.

Package management is a detail. Don't get too hung up on details at this
point. There are not two types of linux. Depending on how you want look at
it, or how you want to categorize, there is either only one linux, or there
are an uncountable number of linux's. It's not like Windows. There is no
overall system written by any one entity or group. There is this big bag of
software parts all written by different people, and most of it has nothing
to do with the rest of it other than it's all written to be compatible and
work according to a common set of general principles, loosely defined as
UNIX, and/or POSIX, and/or in the case of Linux specifically, the LSB (linux
standard base).

Oh I see. Its just the package management..

Much of the sofware in a linux system is not even written specifically for
linux, but is written for any unix/posix compatible system, which includes
freebsd, opensolaris, and a host of commercial unixes like sco, sun, hp,
ibm.

And I am sure Linux is derivative of Unix.

Systems like redhat, debian, ubuntu, suse, etc... these are called
"distributions" not "linux" because that's what they are. They take all the
various components of a typical unix-like system and assemble them into a
coherent system. This is a significant and complex job and it's why
distributions even exist. They have to pick which components to include, and
then customize or configure them to fit into an overall system to work with
other components.

Okay, I really didn't know this before.

For example, one common component of any unix-like system is "getty" this is
a basic program that opens up a tty (a serial port or a console generally)
and prints the login prompt and waits for logins, and hands off the tty to
/bin/login or some other login authentication method and ultimately to a
shell instance (command prompt, ie /bin/sh or /bin/bash).

There are several different getty programs written by different people over
the years with different features and details, although they all do roughly
the same basic job. Maybe one has special support for detecting incoming
faxes or PPP connections on modems, maybe one has support for full-screen
color menu/dialog "pretty" login prompts, maybe one is stripped of
everything except the absolute minimum required to use the vga console only
so it's fast/lighter/smaller, etc.

But the author of mingetty (the minimal getty for use on the local consoles
only) may or may not have written any special systemd support into his getty
app. For example the Makefile for compiling and installing the app, and the
documentation, may just assume that the app will be started from
/etc/inittab and that's it. Suse will have to slightly alter _their_
mingetty package so that it includes a systemd service script instead of one
or more lines in /etc/inittab, and possibly alter the man-page to reflect
that also.

Its really technical (absolutely) but I would really take time to
learn step by step (very slow in my case due to my different job) know
all these, of course of the great technology.

These are all _details_ that are different for every distribution.
They do not make the different distributions into different types of linux.

Ok.

Every distribution has it's own unique pile of these details that makes it
different from every other linux.

And yet, there are certain principles that are the same on just about every
linux. Almost every distribution has the same major _features_ such as
* some version of linux kernel
* some sort of libc
* some sort of init
* some sort of getty
* some sort of ssh server
* some sort of shell
* some sort of package management system

Getting the basic idea....

The ssh serevr is usually OpenSSH, but does not have to be. There are others
and some special purpose distributions use them instead. For instance you
might use Dropbear on a WebOS device or a linksys router running OpenWRT.

The libc is usually gnu libc, but there are others. You would probably use
uclibc on an embedded device or router. You might use a commercial libc with
distributed computing support or support for using gpu's or other special
vector processors on a big cluster.

The package management system might be deb or rpm, or as in the case of
gentoo, most software might be managed similar to the freebsd ports system
where a package is just a set of compile and install instructions and
everything is compiled-to-order on your own machine right when you install
it.

So again. Try not to get too focused on any details yet if this is all new
to you.

Yeah, this is really new to me, I have just installed openSUSE 11.4
and in fact, its outlook I have liked - despite it only took a little
more time to boot..

Go ahead and read distribution-specific books and articles if you don't
happen to find any really good generic ones, but _at first_ don't worry too
much about actual details like program names and file locations and command
line arguments.

All that stuff is subject to change from one distribution to another, and
also changes all the time from one version(*) to the next.

For the purpose of getting started, pick really any distribution, and read
documentation that IS specific to that distribution, and see how things work
and get familiar. You do have to start somewhere. If you're not going to
take a class where a professor will describe general principles abstractly,
then you have to learn by actually playing with something, and there is no
such thing as a perfectly generic linux distribution. Maybe slackware or
linux-from-scratch come the closest. So you will necessarily have to play
with some distribution, which necessarily will be different from all others,
so you will necessarily only partly be learning "linux". You will be
learning "ubuntu" or "opensuse" which just happens to have a lot in common
with other linux's and with other unix-like systems like freebsd and
solaris. But at first you really have no way of knowing what things are
general and what things are specific to ubuntu, or opensuse, etc.

Just as long as you understand that that is what is happening, that should
help you not to be too confused when you come across discrepancies or
ambiguities.

For instance, some document may say "run this command: fdisk <device>"
without saying what <device> is. Frustrating.

Well unfortunately they are not being lazy or unhelpful. They _can't_ say
what <device> is. Not because they don't know. They know, but they know for
themselves, they can't know for you. It's like they know how to buy a new
tire for a car, and they know the exact size of their own tires for their
own car, but they can not know the exact size of your tires for your car. So
they can't give you the full exact directions that you would actually need
in order to actually get a tire that would actually work.

They may supply a "for example /dev/sda1" but you CAN NOT take that and use
it yourself. There is only a small chance that that is correct for you. You
have to know how your own system names it's hard drive devices. In fact, on
linux, the first hard drive is very often /dev/sda only because of a push
the last few years to consolidate the most common disk controller drivers
for scsi, sata, and ide to all use the same driver called libata, abd that
driver happens to use the same naming scheme as most scsi drivers.

But there is absolutely no rule that says disk drive device nodes must be
named /dev/sd<something>, and indeed sometimes they are not. In fact, that's
actually becoming the LESS preferred way to refer to drive devices now.

Now it's usually better to refer to the devices by
/dev/disk/by-id/some-long-drive-maufacturer-model-serial-partition or
/dev/disk/by-uuid/some-long-uuid-number etc.. because nowadays, the way
motherboards and the kernel detects hardware during boot up, it's too
dynamic and variable and user-configurable, you can not count on /dev/sda to
point to the same physical drive from one boot to the next, so you have to
reference something like uuid that is unique to that drive no matter what
order it was detected in at boot time. Also on non-linux systems the names
vary quite widely.

However, the general principles you can apply to almost any unix-like
system, devices are almost always accessed via a special kind of file called
a device node, almost all disks are such devices, and the devices nodes to
access them almost always come in the form of one or
more files under /dev.

Baically, the one core principle of all unix-like operating systems is that
it is made up of a big tool box full of small low level tools that do
specific things. And all high level functionality is built out of connecting
those tools in different ways. It's all intentionally as generic and
non-specific as possible. The "cat" command does not care if it's reading a
file or a tty or a pipe from some other program. It is a generic, low level
tool that does one tiny thing that seems to be pretty useless by itself. And
it is by itself, just like a single Lego block or a single screwdriver. But
combine the screwdriver with a screw and a nut and a couple sheets of metal
and you start to have a higher level object that is good for something. It
might be a dog house or camera or a toilet. And all screwdrivers have
certain principles in common, yet, the exact details, all screwdrivers have
some details different from each other. Unix is intentionally like that.
It's a tool box that you build whatever you want out of. And linux is just
one of several unix-like systems. And opensuse is just one of several linux
systems.

Have I made it confusing and baffling enough ? :)

Not really, but I really got the idea of it, yes especially because I
am a beginner (and get less time), so at times things may look strange
to me... But you have told very nice, I really got an idea of what is
Linux and something related....Its really good to know.. But one thing
I liked is that when you say, 'pick one and start learning its
principles' and that's the only way I guess I can do, yes, of course,
it might take much more time for me (then it usually take for other
--- just because I am in different job).

(*) Heck, the very concept of a "version" isn't even a universal concept.
You asked about the meaning of "rolling release" before. Arch Linux is a
distribution that doesn't really have such a thing as a version. All the
individual packages in it have versions that are always changing, but the
overall distribution never picks any fixed set of packages and says "This
defined collection is Arch Linux version 2.0" Instead all packages are
always whatever is current at the time you install, and they all update to
whatever is current whenever you run an update. That's called a rolling
release. The release is always rolling along, it never stops at any
milestones. This can be a good thing or a bad thing depending on what your
needs and priorities are. It's a live saver is some situations, it's death
in others. This is why there are so many distributions of linux. There is no
such thing as one way of doing things that is best.

Well, got the idea of what is an 'rolling release'.

On Wed, Nov 2, 2011 at 4:22 PM, Anton Aylward <opensuse@xxxxxxxxxxxxxxxx> wrote:

The point many of us make here is that Linux is about basic principles
and putting them together, knowing how things work.

Yes, a better to know and learn how computer works!

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