CentOS is a free operating system distribution based upon the Linux kernel. It is derived entirely from the Red Hat Enterprise Linux (RHEL) distribution.
Adapted from U&L CentOS tag:
The CentOS Linux distribution is a stable, predictable, manageable and reproducible platform derived from the sources of Red Hat Enterprise Linux (RHEL). Since March 2004, CentOS Linux has been a community-supported distribution derived from sources freely provided to the public by Red Hat. As such, CentOS Linux aims to be functionally compatible with RHEL. It mainly change packages to remove upstream vendor branding and artwork. CentOS Linux is no-cost and free to redistribute.
CentOS is developed by team of core developers. The core developers are supported by an active user community, including: system administrators, network administrators, enterprise users, managers, core Linux contributors and Linux enthusiasts from around the world.
Commercial support is offered via a number of vendors.
Using the CentOS tag
Use this tag if your question relates to CentOS security topics; do not use it if you just happen to be using CentOS and your question is about a specific configuration detail or syntax (e.g. a shell script; a web server configuration question; user or group permissions).