Description of problem:
If RHEL 5.5 have only one kernel and I remove his by rpm -e kernel --force, last record in grub.conf are saves. After installing new kernel by yum install kernel, that record in grub.conf still no changed. System boot fail.
Steps to Reproduce:
1. manually remove all kernels (by rpm, with --force if need)
2. yum install kernel
3. check grub.conf
More likely a mkinitrd/grubby problem than a kernel problem.
OTOH removing the only system kernel package with --force isn't treating the system very well... :)
What to do if not enough free space at /boot and this space enough for only one kernel? It is for this case apply the mechanism of removal of a single kernel manually by "rpm -e kernel --force" and the next step is installing a new kernel by "yum install kernel".
You shouldn't remove all of the kernels. Make sure your /boot is larger.