Dnf is already there in fedora which is a test bed for Rhel/centos but why centos 7 is still using yum ?
CentOS 7 corresponds to Red Hat Enterprise Linux 7, released in June 2014. dnf was made the replacement for yum in Fedora 23, released in November 2015. There's no provision for making fundamental changes to a release like that. Changes made within a release are incremental, perhaps adding features, but never removing existing features and replacing them by others.
A future release of CentOS likely will have
dnf unless Red Hat chooses some other tool by the time Red Hat releases version 8, etc.
During the three-year Production Phase, qualified Critical and Important Security errata advisories (RHSAs) and Urgent and Selected High Priority Bug Fix errata advisories (RHBAs) may be released, as an update to the Red Hat Enterprise Linux Atomic Host image,as they become available. Other errata advisories may be delivered as appropriate.
If available, new or improved hardware enablement and select enhanced software functionality may be provided at the discretion of Red Hat, as an updated image. Updated Red Hat Enterprise Linux Atomic Host images are cumulative and include the contents of previously released updates.
The Red Hat Enterprise Linux life cycle phases are designed to reduce the level of change within each major releasei over time and make release availability and content more predictable.ii
- 1. What is CentOS Linux? (FAQ)
CentOS conforms fully with Red Hat, Inc's redistribution policies and aims to be functionally compatible with Red Hat Enterprise Linux. CentOS mainly changes packages to remove trademarked vendor branding and artwork.