On Sep 3, 2010, at 4:10 PM, Marko Vojinovic <vvmarko at gmail.com> wrote: > On Friday, September 03, 2010 18:34:51 Matthew Miller wrote: >> On Fri, Sep 03, 2010 at 12:17:37PM -0500, Les Mikesell wrote: >>> Does anyone know if this is special-cased or some config setting? I >> >> It's special-cased. > > I remember the discussion on the Fedora-list about this a very long time ago, > and the bottomline is roughly the following: > > * when a yum update installs a new kernel, it checks if the total number of > installed kernels exceeds the installonly_limit parameter > * if not, everything is ok > * if yes, the oldest *non-running* kernel is removed and the remaining number > of kernels is checked again against installonly_limit, and the removal step is > repeated if they still don't match up. > > This was done precisely because it was understood that a currently running > kernel can be assumed to be stable and bootable. So if you have several > kernels, run a yum update while the oldest one is running, get a new kernel, > the extra kernels that will get removed are those "in between". This ensures > that with any multiple-kernel configuration of yum, there will be at least one > kernel known to work, as a failsafe. > > I believe CentOS just inherited this behavior of yum. Though I might be wrong, > it seems unlikely that anyone would remove this feature from yum on purpose. > > So all in all, you should never be afraid that yum will leave you only with > untested kernels while updating. This is good info! What I am wondering is if there is a way to prevent new kernels from becoming the default by... default? That way one won't be "pleasantly" surprised that after a long uptime and several updates, that on the next reboot their applications stop working because of a kernel update that hadn't been tested yet. A way where the admin must manually choose the default kernel. -Ross