升级linux内核时，2.6.21.5内核编译成功，但启动时出现panic，请看问题详细描述！
原有系统：Red Hat Enterprise Linux AS (2.6.9-34.EL)
升级到内核版本：2.6.21.5
内核编译时成功，并且make install 后也自动更新了/root/grub/grub.conf文件，该文件内容如下：
#boot=/dev/hda
default=1
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title Red Hat Enterprise Linux AS (2.6.21.5)
root (hd0,0)
kernel /vmlinuz-2.6.21.5 ro root=/dev/VolGroup00/LogVol00 rhgb quiet
initrd /initrd-2.6.21.5.img
title Red Hat Enterprise Linux AS (2.6.9-34.EL)
root (hd0,0)
kernel /vmlinuz-2.6.9-34.EL ro root=/dev/VolGroup00/LogVol00 rhgb quiet
initrd /initrd-2.6.9-34.EL.img
但是我以2.6.21.5内核启动时，出现错误，错误信息如下：
/proc/misc: No entry for devicemapper found
Is device-mapper driver missing from kernel?
Failure to communicate with kernel device-mapper driver.
0 logical volume(s) in volume group "VolGroup00 " now active
mount: error 19 mounting ext3
mount: error 2 mounting none
switchroot: mount failed: 22
umount /initrd/dev failed: 2
kernel panic - not symcing: Attempted to kill init!
[解决办法]
Is device-mapper driver missing from kernel?
[解决办法]
因为你的磁盘做了LVM，编译内核时记得选中 LVM support
