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I was just reading about Linux servers and Red Hat Enterprise Linux. What exactly is the Red Hat Network (RHN)? From what I've gathered, you subscribe to it to be able to update your system. Does this mean that you won't be able to update the packages (using yum) if you don't have a subscription? Doesn't yum just look in repos just like apt-get in Debian distros? Pardon me, but this is coming from an Ubuntu Desktop user, so I'm used to a simple apt-get upgrade to upgrade packages; I don't know much about the server side of Linux, let alone Red Hat-based distros. Also, is this RHN subscription a paid one?

Also, how does CentOS differ from RHEL? Which is used more commonly as a server?

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Yes, RHN is pay for. But you're not so much paying for the packages you can update as for the ability to contact them for support. Centos is using the exact same packages (minus a few proprietary things from RHEL), but you can't hold anyone responsible for problems. –  tink Apr 29 '13 at 18:55
@tink, sorry to say this, but your comment looks like a valid answer :) –  Deer Hunter Apr 29 '13 at 19:10
@tink what "proprietary changes" are you referring to? It's GNU GPL so Red Hat has to release the source code, that's actually how CentOS gets the source code they're compiling from. Red Hat can't stop them as long as the CentOS project doesn't infringe on the trademark. Which still isn't being proprietary as much as insisting that people not say they're something that they're not (i.e unintentionally commit fraud). –  Bratchley Apr 29 '13 at 19:20
Talking about their graphics/splash screens. –  tink Apr 29 '13 at 19:43

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RHN is to RHEL what "WSUS" is to Windows. It's just the mechanism used to push updates out to clients and for those clients to pull new packages/updates down from. It presents to the client systems via a yum plugin and so from the system administrator's point of view all the packages available on RHEL just look like they're coming from a regular yum repository.

You need a subscription to do RHEL updates, but it's not strictly required. If you're only concerned with system update, CentOS might be a better fit. Regardless of what they say, they do change stuff around (sometimes beneficially) and they include extra packages that don't have the same level of QA that Red Hat puts into their RPM's. You also lose out on some of the features you get from the web interface to RHN where you can review and schedule updates, group them, etc. You also lose out on web/phone support and if a bug is creating a sev1 issue for you, then you're on your own.

But for the packages common to both distributions, CentOS is 90-95% repackaged and rebranded RHEL. If your goal is just system updates and none of the other stuff, that's what you should be looking at.

For which one is more common, it's anyone's guess. No one really tracks hard numbers on that stuff. Having a RHEL subscription is obviously ideal so you do get the extra stuff (makes managing many systems much easier) but CentOS is also designed for people who are budget-centered and can self-support. RHEL is pretty ubiquitous in high end data centers, but there are lots of mom and pop shops that use CentOS. It's kind of hard to tell which out weighs the other (install base-wise).

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So basically, RHN subscription = managed updates + web/phone support, neither of which are found in CentOS. Though, this doesn't mean I won't be able to update my packages if I don't have the subscription, right? I'll still be able to run yum to update packages on RHEL, just like I would on CentOS. –  Alaa Ali Apr 30 '13 at 5:58
Well RHN is technically just the "managed updates" part, the web/phone support is just another service given as part of the subscription. But there aren't any means of updating the RHEL base OS without a subscription. If you want to do that then you needed to have used CentOS at install time. Given the large amount of overlap between the two, I'd imagine there's some way of putting CentOS repos on RHEL and just gradually updating into CentOS if you looked for it online, but that seems dicey. It would be better to just install and stay with CentOS if you're only looking to get updates. –  Bratchley Apr 30 '13 at 12:00
Basically: RHEL is the thing you use if you know you're going to want to use management stuff like RHN, will need web support, need a certified platform for some application you're going to run (like Oracle), or need absolute assurance that all packages installed have gone through a rigorous QA process. CentOS is for everyone else –  Bratchley Apr 30 '13 at 12:03
@JoelDavis - yet have a look at this: serverfault.com/questions/497049/… –  Deer Hunter Apr 30 '13 at 18:45
Yeah that OP might be insane, he's definitely irrational. He says "except downgrading kernels not an option on RHEL 6.4" without really explaining why it's not an option for him, you can have more than one kernel installed. He also blames RH specifically for a bug without possibly knowing enough details to know they're responsible and they didn't just backport something upstream. So he has a solution to a problem of statistics reporting, doesn't want to use it for some reason, acts as if he know Red Hat are the ones doing it, and is screaming at the top of his lungs. –  Bratchley Apr 30 '13 at 19:03

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