I mean that ex.: CentOS, and Scientific-Linux are the "exact copies" of Redhat Linux. If Redhat would say one day: "I don't allow Redhat clones from now on, I will modify the licence", then what would happen to all the Redhat based distros? I mean the ones that are really just "clones" of Redhat?
How does this "Redhat clone" thing work? Redhat makes Redhat 6 downloadable freely? And then some people compile the Redhat 6 sources (with a few modifications), and presto, the "Redhat clone" is ready? Or how do they get the source codes of Redhat 6?
There were precedents like:
https://en.wikipedia.org/wiki/Red_Hat_Enterprise_Linux#Rebuilds
"Unusually, Red Hat took steps to obfuscate their changes to the Linux kernel for 6.0 by not publicly providing the patch files for their changes in the source tarball, and only releasing the finished product in source form."
So the Q: If Redhat would change the licence of RHEL, all the Redhat clone distros would permanently die? (just in theory, hopefully something like this would never occur)
Best Answer
Short answer, they legally can't do that.
Most of the code in RedHat, like all Linux distros, is GPL-licensed, including the kernel and most (all?) of the core utilities. They can't release it under anything but the GPL, and so long as they distribute the binary they have to distribute the source. That also means they can't prevent anyone from cloning it (besides the trademarks, of course). That is one of the big points behind the GPL.
The "precedent" you specified in no way constitutes not releasing source under the GPL and has absolutely no impact on clones. They just didn't release the patches individually, they did release the entire (patched) kernel, making anyone who wanted their patches (in this case directed at Oracle, it seems) put in a little extra work to do the
diffthemselves and sort out which code changes go with which fix.