Before we go anywhere, I wanted to say that I hard a hard time writing this article. The reason I say this is because CentOS and RHEL are essentially the same thing. Both distro's use the same binary package format (RPM). Both use the same kernel version (I briefly discuss what a kernel is below). Both use the same versions of critical system packages
including glibc, zlib, openssl, coreutils, which are coincidentally free software that can be downloaded, built, and distributed as RPM's by anyone compelled to do so. Really the only big difference is the mandatory support bundled with RHEL.
Supported users of RHEL can use the provided up2date application to install, and/or upgrade different RPM packages, including the kernel. Supported users also receive membership to the "RedHat Network". The RHN compliments up2date by providing user's with priority update email notifications, errata, and an automatic update facility. CentOS users also have a similar application called "yum", which is detailed below. Depending on the level of support included with your RHEL purchase you are entitled to phone, and or web-based/email support.
CentOS does not provide any "official" support. However, there are many (archived) mailing-list and forum posts that share the same knowledge for free. Granted, it may take slightly longer to find the answer if you are the one actually posting to a list with your issue. This is exactly why we provide our own support services (for a nominal fee). One of our
skilled server administrator's can login to your server, resolve the issue, and then show you the steps taken to fix the problem, were it ever to recur. I was not able to find a figure for RedHat's support time-to-resolution, however they do guarantee time-to-respond (depending on the level of support you have). We guarantee a time-to-respond of 1 hour or less and our time-to-resolution via our support portal, on average, is slightly more than 1 hour.
CentOS does provide "supported" updates. Not because CentOS officially supports them, but because they are supported (tested/proven stable/secure) with the distribution's base and committed as stable. Instead of 'up2date', 'yum' is used with CentOS. In the end, both of the package management systems complete the same upgrades. Actually, it strikes us as funny, because both package managers install the same RPM's, the exact same versions, built with the same compilers, with the same tree of dependencies. For those who do not already know, RPM is the RedHat package management system, which is similar to an .msi installer in windows.
In addition to our General Management Package, SingleHop also offers kernel and OS updates. It's true that we do use the package manager to update the applications included with the operating system, but we install a custom kernel with additional security and scalability features to every server. Also, we are very attentive to the security community, so as soon as a new vulnerability is discovered, we are ready with a workaround and/or patch.
Speaking of kernels, now is a better time than ever to explain what a kernel consists of and to denote the differences between the CentOS and RedHat kernels. A kernel or an operating system kernel, is the interface between software and hardware. The kernel is also responsible for managing process scheduler and TCP/IP stack. If you don't want that
means, imagine your car without the engine. The kernel used in CentOS is identical to the kernel used in RHEL; both are based on the 2.6.9 tree and are heavily patched. The Linux kernel is released under the GPL (GNU Project General Public License), so RedHat is required by the terms of the GPL to release any modifications that they make to the kernel source to the open source community.
At Single Hop we are more than capable of supporting RHEL, CentOS, Debian, Fedora, FreeBSD, Gentoo, SuSE, or even Slackware. We specifically recommend CentOS for a few different reasons. Of these, the main reason is consistency. Nearly 90% of our Linux servers are currently running CentOS. Using the same distribution allows us to test updates on staging servers before applying them to your production machine. CentOS also functions perfectly with cPanel, which is our recommended hosting control panel.
Hopefully the article above answers your questions on the differences between the two operating systems. If you have any questions or would like to discuss this issue further, please feel free to contact us at firstname.lastname@example.org!