I am trying to figure out the technical differences between Linux distributions, specifically debian vs yum based distros (centos, fedora, redhat).

As far as I understood, the main differences are mostly located in packaging (policies) and kernel patching. How each distro compiles the kernel, how often a new version of the distro is released, how each distro updates kernel.

However, I cant find any further information for the above and generally any other technical difference on the two distros. Most of the information I find is very descriptive, for instance:
X distro is stable,
Y has latest packages
e.t.c

Can someone pinpoint important technical differences which can make a sysadmin to prefer one from the other?

Does each distro compiles and updates the kernel the same way or are treated differently?

For example, I heard a colleague saying that a particular yum based distro (cant really remember if it was redhat or CentOS), would support one of their releases which comes with a Linux kernel 2.6, for, say 8 years. Now, the way they update the kernel, after a couple of years you end up having a 2.6 kernel with features of 3.x (assuming a new major kernel version has been released). So he stated that this was one of the reasons he picked up debian. What I understood is that debian has a more "clean" (from version-features perspective) kernel. Is that correct?

No.

The differences have a lot to do with the preferences and philosphies of the distro maintainers and/or purpose and while there are some technical differences based on those preferences there are just as many non-technical reasons. Some distros (e.g. RHEL/CentOS) are maintained more for stability. Some distros (e.g. Fedora) are meant to be bleeding edge. Some distros won't take anything that has trademarked logos so will use forks of packages (e.g. Iceweasel vs Firefox, Lesstif vs Motif).

So in the end it comes down to which distro most closely matches YOUR preferences and philosophies and purpose. (e.g. If you're using it for business often you are more interested in stability, if you're using it for self education and don't mind updating completely every 6 months you might prefer something more bleeding edge.)

If you don't like any of the distros that exist you can make your own but then you have to maintain all the updates. Some people like doing that.

As an FYI RHEL = paid RedHat Enteprise Linux subscription, CentOS = unpaid compile from RHEL sources (in general open source requires that one provide source if they modify it which is why CentOS can exist).

Your friend is somewhat correct on the RHEL/CentOS idea. They maintain a "major" release (e.g. RHEL5, RHEL6, RHEL7) for several years. In general any packages maintained in that "major" release do not get updated to new upstream versions (e.g. RHEL5 and RHEL6 are both based on 2.6.x kernels, RHEL7 is based on 3.x kernel) but rather backport upstream security and bug fixes (and sometimes enhancements) into the lower version they run and they put extended versioning in the package names to show different versions of the same upstream package. The idea here is stability. Many business processes couldn't be changed rapidly. The downside is that sometimes features you may want don't exist in your "stable" version. (e.g. RHEL5 did not allow for TLSv1.1 or TLSv1.2). RHEL5 by the way went end of support at the start of April. RHEL6 and RHEL7 are supported. This versioning is not just for the kernel. You might see it for Java, PHP, Postfix, Perl and most packages.

In the meantime Fedora is bleeding edge so you'll have fully updated version of kernel and all packages every 6 months which is an aggressive upgrade cycle for business but fine for many other things.

Ubuntu which is derived from Debian goes its own way and often going from one release to another causes much gnashing of teeth. (e.g. A few years back a lot of people complained about its windows manager going away from Gnome and now a lot are complaining that they're dropping its Windows Manager.

In general you can do much of what you want in most Linux distros but if you have specific purposes in mind you should look to see what you think will most likely match that purpose.

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Also, note that "the kernel" is really a very small part of the overall ecosystem: it is the always-resident layer of programming which controls the actual hardware and which creates the environment in which "user-land" programs can run. The differences between one distribution and another have to do with the ecosystem of software that surrounds the kernel, such as maintenance utilities and some distro-specific programs. The suppliers of a distro undertake to provide technical support for each version for a number of years before finally "sunsetting" it.

For enterprise customers, the distro-makers do a whole lot more. For instance, since day-one Red Hat targeted the corporate installation, and their steadily-profitable business model is unabashedly "pay to play." The makers of Ubuntu, likewise, will shine-your-shoes if you pay them enough. Some companies run literally thousands of computers, sometimes on virtualized hardware that they do not own, and these companies supply tools (and contracted support services) which make that possible. For the intended corporate customer, it's simply a cost of doing business and well worth the money spent.

https://debian-handbook.info/browse/stable/
http://codesearch.debian.net/

comparing kernels more or less useless, because there are also modules and they are running on different hardware, so hard to say anything about the stability of ... exactly what?
Usually the same version means the same bugs, same security issues and same features.

This sounds like it is for an Enterprise focus and so as far as Enterprise goes, my opinions go...

I'd recommend RHEL or CentOS over others but it comes at a huge cost, to be stable these distributions ship very out-of-date software and so security updates have to be backported. This is before it is even released, for example RHEL 7 comes with a 3.10 kernel (3.15 was current at release, 4.10 is current now), Python 2.7 and the most obvious one being PHP 5.4 which went EoL only around a year after RHEL7 was replease. The advantage of not upgrading these packages to the current versions however is that then things on the servers do not break that often.

CentOS lifecycle is usually based off of RHEL given what CentOS is. RHEL's life cycles are all available at: https://access.redhat.com/support/policy/updates/errata

Ubuntu LTS usually comes in after that, it has a good 5 year long life cycle and the ability to upgrade to newer LTS versions when they become available. Naturally as Ubuntu LTS is a 2 yearly release, it won't be bleeding edge but will usually be much more up to date than CentOS/RHEL and so for things using newer packages/libraries, this is preferable. More so newer features.

Debian only has a 3 year long life cycle which from an Enterprise standpoint is a little low.

If I understood correctly, the actual difference of distros is spotted on:
1) Release cycle. How often a new version of the particular distro is released.
2) Packages. Maintaining and updating upstream versions.

To a large part but as I also noted a lot has to do with the philosophy and purpose. One distro may include (or provides via repositories) packages that another refuses to include or provide.

However, as noted one can often get those packages form other locations (e.g. the upstream provider's own site) and compile their own or their may be 3rd party folks that provide the packages. For example Fedora maintains the EPEL which is a repository of packages one can add to RHEL (or CentOS) that are not part of the official RedHat supported package set but will run just fine on RHEL.

Is there any link or article which compares debian vs centos package philosophy or do i have to read the documentation of both distributions and find the differences?

Most distros are forks off Debian. Red Hat, Centos and Fedora are essentially the same thing, but not like Debian. Debian is the reference standard operating system, because it has:

the most mirrors (most widely available)

the most software packages

the greatest amount of documentation

the greatest number of developers

runs on the largest number of processor architectures (everything from embedded appliances to Cray Supercomputers)

totally free of self-interest (i.e. is not seeking to earn income directly from users, through tech support, pre-made CD/DVD sales; nor is it tied in any way to any corporate interests.

It is the most secure, employing the Debian Web of Trust

It is the most widely used

But without commercial motivation there exists no recourse--other than bug reports--for the user to get what they need from Debian.

It's also like diving into the middle of the ocean for a swim. You might not need the whole ocean. Maybe a pool or a beach might be more suited to most people. Within Debian are Debian Pure Blends that are more focused to a certain type of task.

Red Hat, Centos and Fedora work really well using the RPM package manager. It is a phenomenal tool. But all three have an enterprise focus. I doubt if you'll find many packages aimed at microwave antenna design or gene mapping.

But if that's what you want, you can install from source. Practically any Linux program can be installed in any distro. I learned Linux using SuSE 7.2. I run Debian testing on my laptop, because I don't mind messing around a bit in case of a bug.

On other machines I run Debian stable, Fedora 24, Opensuse 11.3, and Ubuntu 16.04. Anything I can do with one I can do with all of them. The Debian philosophy is to be beholden to no one. Total neutrality.

Fedora is the development branch of Red Hat. After everything is working in Fedora, it becomes Red Hat. Centos is a renegade fork off Red Hat.

Every main distro makes some of its own kernel patches. It's become more troublesome as of late, especially when Debian put gcc6 into the testing branch and broke the kernel compile.

I use to put a pristine kernel from kernel.org into Fedora 6, and it worked perfectly fine. Debian is the fussiest about kernel compiles lately.

The kernel turns bytes on the disk into processes in memory. Usually, if the kernel compiles, it will work. Between distros there is not much difference in the kernel except the version.

I strongly disagree.

First off Fedora is bleeding edge where RHEL and CentOS focus more on stability. You also leave out other RPM based distros like Scientific Linux. Even within the distro the major releases can have significant differences (e.g. RHEL7 was the first to rely on Systemd in the RHEL family.) You also don't mention so far as commercial 3rd party support for business goes RHEL has the lion's share.

I also disagree that most distros are based on Debian. Ever heard of Suse? Slackware?

In fact Debian came around long after I first heard of Slackware and RedHat.

Although Ubuntu and its derivatives are based on Debian it is a very different animal than Debian under the covers.

Don't allow being a fan of one distro blind you to the rich diversity of distros that are available.

There may be but I don't know them off the top of my head. Doing some web searches on "Debian vs Redhat Philosophies" might lead you to things like:
https://www.quora.com/What-are-the-t...d-Debian-Linux

I can sum up the main CentOS raison d'etre as being a binary compile of RHEL sources that does not require a RHEL subscription. i.e. In essence an attempt to be a "free" distro where RHEL is a commercial distro that charges you for updates.

Just remember almost anything you read (including my posts and various articles) is going to be laced with opinion of the author. The above link shows a bias as do the comments on it. You can look for a side by side comparison of commands but even that might be off unless it tells you which specific versions of distros are being compared.

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But maybe it's worthwhile to consider the differences between the various corporate business models.

RedHat (stock symbol: RHAT) started at day-one ... (yes, I was there, just as I was with AAPL) ... with a purely revenue-assured-based business model. Nothing was free, except the obligatory Fedora. However, there was a promise to go along with that profit: "Mister Corporate Customer, we will (always be able to afford to) take care of you." And so they did.

They were a very successful IPO ... ... because their revenue model was always very explicit – and, very old school. If you were anywhere in their playing field, "yes, you got 'free' popcorn," but it was always known that you had bought a ticket subscription.

They never flinched from "pay to play." However, unlike every single company that I so-far have ever gotten "stock options" from, they could say that "we will be here, tomorrow!"

- - -
And, please note, "by this I am not saying that there are not other equally-valid market strategies!" Mark Shuttleworth, for instance, certainly is no fool . . .

RedHat was originally free from 1994 and still allowed at least one free download and updates of same until 2003 when it discontinued RedHat Linux and rebranded that as Fedora. At that point the commercial product was RedHat Enterprise Linux (RHEL).
https://books.google.com/books?id=Bl...0-rhel&f=false

RedHat didn't go public until 5 years after it was first created (and after a merger with another company).
https://en.wikipedia.org/wiki/Red_Hat

I recall when I started using RedHat regularly in 2004 there was still much gnashing of teeth about the RHEL/Fedora split with many saying RedHat had betrayed Open Source Linux. Since then most seem to have mellowed on that attitude given that Fedora remains "free" and RedHat has contributed much back into the FOSS community. They've even taken CentOS which used to be a separate project in house and continue to support that project.

Their all technically the same as they all use the same kernel (just different versions of it). The main differences are in the UI and other high-level components.