In November, with the release of Red Hat Enterprise Linux 6, the company released its kernel package with all patches pre-applied. "In the past, we distributed the kernel as a base file and then a set of add-on patches that accompany it. Then when you did a build, the build process automatically applied all those patches to the kernel file," Stevens says. "Now, we integrate those patch files directly into that kernel. We do the first part of the build process prior to distribution."
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"The changes will make work harder for distributions such as CentOS, the community-built Linux distribution ... based on Red Hat's sources," H Online said. "CentOS is built from the RHEL source by a limited number of volunteers and Red Hat's change in policy will mean more work for them unless more volunteers or other companies step in and provide them with assistance."

It may be that SL has a larger user base, and won't be impacted as much as CentOS.