To determine when a Red Hat or CentOS server was first built, use rpm -qi basesystem:
[fred@rhel7 ~]$ rpm -qi basesystem Name : basesystem Version : 10.0 Release : 7.el7 Architecture: noarch Install Date: Thu 16 Apr 2015 18:16:04 CEST <----- here Group : System Environment/Base Size : 0 License : Public Domain Signature : RSA/SHA256, Tue 01 Apr 2014 15:23:16 CEST, Key ID 199e3a91fd554c52 Source RPM : basesystem-10.0-7.el7.src.rpm Build Date : Fri 27 Dec 2013 18:22:15 CET Build Host : xxxxxxxxxx Relocations : (not relocatable) Packager : Red Hat, Inc. Vendor : Red Hat, Inc. Summary : The skeleton package which defines a simple Red Hat Enterprise Linux system Description : Basesystem defines the components of a basic Red Hat Enterprise Linux system (for example, the package installation order to use during bootstrapping). Basesystem should be in every installation of a system, and it should never be removed.
Note: The date returned, 16th April in the example above, reflects the time that the operating system was installed. This is usually the same as the system creation time, except in cases where a system has been cloned or built from a pre-installed image. In the last case, the date returned will reflect the build date of the source image, rather than the target system.