unable to find the sources of your current Linux kernel. 解决

运行

sh ./VBoxLinuxAdditions.run

时FAILED，查看日志：

/tmp/vbox.0/Makefile.include.header:97: *** Error: unable to find the sources of your current Linux kernel. Specify KERN_DIR=<directory> and run Make again.  Stop.
Creating user for the Guest Additions.
Creating udev rule for the Guest Additions kernel module.

意思是说没有内核源文件，解决的办法是运行

yum instal gcc.i686 kernel.i686 kernel-devel.i686
reboot

分别是编译器，内核，内核头文件以及Makefile，然后再重启，让系统从新的内核文件选项启动。再运行

sh ./VBoxLinuxAdditions.run

就可以编译成功了。