Mystery Solved! Karanbir Singh gave a clue by suggesting the dsiabling of the splash screen at which point the magic word "LILO" flashed up briefly on the screen. It appears that the machines which were affected all had lilo installed but not configured as bootloader. These machines are all configured identically using a kickstart script. This script does not have lilo enabled in the bootloader. How they actually came to have lilo installed is a bit of a mystery as all the rest plainly do not have it. However when the kernel update was installed by yum, it looked for a bootloader & picked on lilo instead of grub in machines with lilo installed. I the log files of affected systems: Kernel Updated/Installed, checking for bootloader Lilo found - adding kernel to lilo and making it the default Thanks for help Les -------------- next part -------------- A non-text attachment was scrubbed... Name: L.Oswald.vcf Type: text/x-vcard Size: 354 bytes Desc: not available URL: <http://lists.centos.org/pipermail/centos/attachments/20050921/7e894bec/attachment-0005.vcf>