If you are not running a customer kernel (if you don't know the answer its probably no), then running yum -y update is good, however if you have experiences like most of us and find that kernel updates panic and wont boot, then you need to put in a failsafe to fall back to the old or previously working kernel to save you having to wait for someone to reboot at the datacentre or via KVM, so ...
Originally Posted by assassin85
before rebooting, edit grub.conf and add ...
to the end of the kernel version lines, i.e....
Then run this command from SSH as root...
# grub.conf generated by anaconda
# Note that you do not have to rerun grub after making changes to this file
# NOTICE: You do not have a /boot partition. This means that
# all kernel and initrd paths are relative to /, eg.
# root (hd0,0)
# kernel /boot/vmlinuz-version ro root=/dev/sda1
# initrd /boot/initrd-version.img
title CentOS (2.6.18-53.1.4.el5)
kernel /boot/vmlinuz-2.6.18-53.1.4.el5 ro root=LABEL=/ panic=5
title CentOS (2.6.18-8.el5)
kernel /boot/vmlinuz-2.6.18-8.el5 ro root=LABEL=/ panic=5
echo "savedefault --default=1 --once" | grub --batch
This will force a reboot on the next kernel version in the list if the latest one panics and fails to load. And then you can remove the update that failed to boot...
obviously use the correct version number in the above example.
yum remove kernel-2.6.18-53.1.4.el5
And then you will want to exclude that version from subsequent updates when using yum, so add an exclude in your yum.conf [MAIN] section...
again, obviously using the correct version number in the example above.