FAQ
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?

Thanks,

Jon

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  • Mark Roth at Sep 19, 2011 at 11:38 am

    Jon Detert wrote:
    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?
    Never has been a full release upgrade path - that's a bad idea, too much
    cruft.
    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)?
    Yum update *will* do that without a problem.
    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?
    No, you're not. It will update /etc/grub.conf (a link to
    /boot/grub/grub.conf), and the next time you reboot, it will default to
    the new kernel. It does remove the oldest kernel, but leave (I believe) at
    least three (current, and the last two).
    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?
    New kernel.
    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?
    Tune /etc/yum.repos.d to point to explicity subreleases is, I think, the
    answer.

    mark
  • Isdtor at Sep 19, 2011 at 11:39 am
    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)?
    Yes if you configure the repositories in /etc/yum.repos.d accordingly
    (i.e. use the vault).
    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?
    Kernels are installed side by side. For the second question, see
    /etc/sysconfig/kernel.

    In theory you should be able to mix and match any components from the
    same CentOS major release without problems, unless any of the release
    notes say otherwise. Whether it's a good idea is a different matter.
    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?
    New glibc requires a reboot. Upgrading other system libraries does
    too, but I can't give a definite answer on the how to tell. ldd
    /sbin/init indicates the libselinux and libsepol packages are other
    candidates, but that's just one example.
    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?
    See the answer to 2).

    Other people will give you some flak for these questions as it's
    generally recommended to run the latest version.

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