Been using UNIX since the late 80s; Linux since the mid-90s; virtualization since the early 2000s and spent the past few years working in the cloud space.
Location
Alexandria, VA, USA
Education
B.S. Psychology from Pennsylvania State University
Fedora is the upstream, comminity-driven project for Red Hat Enterprise Linux. Not everything you see in Fedora reaches RHEL, but it's where many of the ideas that end up in RHEL come from. Translation, your "Based On" column is inverted.
CentOS, as with Scientific Linux, Oracle Linux and a few others are based on RHEL. CentOS (and SciLin) both create themselves from the Red Hat published source-RPMs and don't really otherwise deviate from RHEL other than by "branding" and support models. Oracle takes the RHEL sources and makes so "strategic" modifications - most notable being their Oracle Unbreakable Kernel (which, among other things, implements the KSplice functionality that they bought and took closed-source).
In general, "expertise" for a given distro depends heavily on what you're trying to use the OS for. If you're supporting an Enterprise application or a workload that isn't well-aligned to a given distro's design-philosophy, the expertise-required goes way up (e.g., if you're trying to maintain a bleeding-edge development environment, RHEL/CentOS can be paaaaaaainful when trying to to keep your language packages — and the like — something resembling "current"). If you're just using a given distro as a casual-use system, the expertise required generally trends markedly downward.
Another thing that ought to be a point of consideration for a distro-choice is, "how much of what I learn about this distro can improve my employment options and potential salary". =)
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Might want to update your table a bit:
In general, "expertise" for a given distro depends heavily on what you're trying to use the OS for. If you're supporting an Enterprise application or a workload that isn't well-aligned to a given distro's design-philosophy, the expertise-required goes way up (e.g., if you're trying to maintain a bleeding-edge development environment, RHEL/CentOS can be paaaaaaainful when trying to to keep your language packages — and the like — something resembling "current"). If you're just using a given distro as a casual-use system, the expertise required generally trends markedly downward.
Another thing that ought to be a point of consideration for a distro-choice is, "how much of what I learn about this distro can improve my employment options and potential salary". =)