Although differentiation is tough in Linux distributions today, CentOS 7 has carved out a niche as the free and open alter ego to Red Hat Enterprise Linux (RHEL). We found that CentOS, which is mandated to be binary-compatible with Red Hat 7, shares about 95% of the features of its commercial enterprise-class sibling.
There's no IBM System z port, and special variants for cloud and virtualization are more limited than with Red Hat 7. But for many common and generic applications, it's a drop-in replacement.
The primary differences for most IT admins, systems people, and engineers/developers will be a (purchased) relationship with Red Hat and Red Hat's army of supported applications, working partnership projects and management skills.
CentOS 7 is perhaps most aptly put as the DIY twin of RHEL7--who lives in the distro ghetto across the railroad tracks.
Still, in testing different deployment payloads, and also where we chose GUIs, the look and feel between Red Hat Enterprise Linux and CentOS 7 instances were essentially the same. And the same mistakes made to either usually cause the same explosions.
You might or might not find the fix faster in a Red Hat resource. The Centos.org website doesn't have Red Hat's polish, and has many odd links to nowhere or nothing--not 404s, rather, unfinished projects. The CentOS site seemed comparatively untended to us.
What you get
There are desktop and server-focused CentOS 7 in varying sizes, and you'll need an x86_64 64-bit processor. We could not find ARM (now in Debian and Canonical resource pools) or System z ports (favored by SUSE and Red Hat).
Yes, CentOS 7 uses what some Unix-o-philes and Linux admins feel is heresy, the systemd and systemctl resource flow controller daemon. We're officially neutral on this issue.
CentOS 7 comes available either as rented/leased/spun-up cloud instances of varying builds available from your favorite cloud host, or in one of several download-able flavors in server or GUI (desktop-focused) versions.
An OpenNebula cloud version wasn't available at testing time, and so a cloud-able version under OpenNebula will have to wait. There are desktop versions available that use either Gnome or KDE as UIs. The desktop versions weren't the focus of our review, but refugees from Ubuntu or those seeking alternatives to Linux Mint may find them interesting.
The very convenient CentOS 7 Everything ISO (with a Gnome default UI) is 6.3GB, but it can be whittled down upon installation (then cloned if needed), as the installation choices almost mirror those of RHEL7's, ranging from minimal to ConquerTheEarth (web, dev, management, databases, plentiful tools, and the kitchen sink).
You can make thick builds, targeted, or skinny ones, then replicate them (importantly: at no Red Hat license instance cost) to your heart's content. The smaller build works fine for more "core" applications, and either can be used to generate PXE-bootable builds, too. Also available are ways to boot from a SAN.
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