I'm pretty new to the task of upgrading CentOS or RedHat o.s.'s. I'm more familiar with upgrading Debian based o.s.'s. Here are my questions:
1) will yum ever upgrade the major version? I understand that there is no upgrade path from v5.x to v6.x, but is that always the case? e.g. was there an upgrade path from v4.x -> v5.x? If yum is capable of doing so, what are the command-line arguments necessary?
2) can I upgrade a minor version to any other greater minor number, or only to the greatest? E.g. if i have a v5.4 box, can i upgrade to v5.5 or v5.6, or only to v5.7 (currently the latest)?
3) if an upgrade delivers a new kernel, am I obligated to run it (i.e. will the old kernel remain installed, or will the upgrade remove the old kernel)? If not, does the upgrade automatically update grub such that the new kernel becomes the default? Will the upgraded box function properly without running the new kernel?
4) aside from when an upgrade includes a new kernel, how can I tell when a reboot is necessary? I gather that a new glibc may require services to be restarted, but is a reboot strictly necessary?
5) is there a way to apply only the updates that were made for the given minor version you're currently at? E.g. if I'm at v5.5, how can I only apply updates that were made prior to v5.6's availability?