About grub.conf
In centos6 or lower version, grub.conf file defines the system boot menu option, the equivalent of 7 and 10 windows installed at boot time to let you select a system boot, as the contents of the file is as follows: 
in Configuring the figure, default timeout and two are to be configured, title is a must have,
write behind the kernel places the kernel files are stored (if the boot is individually mounted in a separate partition, you can directly write / kernel the file name; if not in a separate partition mounted on the path, then we should write the full name, followed by the root = root directory of the mounted device name or uuid plus some kernel parameters; initrd followed by the need to start the kernel pseudo-root; optional other items wherein the password is optional password provided behind the access code is a single-user mode is to be entered, an example of a grub.conf.
The impact grub.conf file error generated
When the file error occurs, the system will appear directly in the boot
grub> Means grub.conf file is missing or wrong
Boot repair process
When you encounter this situation can not be switched, there are two solutions.
Option One:
Modified directly on the interface error
kernel /vm***********(内核文件） root=根挂载点
initrd /init*******(伪根文件）
boot This approach allows the system can boot, but this is only loaded into memory inside, in order to properly start the next boot, you need to modify the grub.conf file.
Option II:
Boot into rescue mode, chroot cut the root, then directly modify the grub.conf file.