initramfs (RHEL 6)

dracut utility can be used in RHEL 6 to rebuild the initrams image ,It  creates  an initial image used by the kernel for preloading the block device modules (such as IDE, SCSI or RAID) which  are  needed  to access the root filesystem.


1.       It is recommended you make a backup copy of the initrd in case the new version has an unexpected problem:

# cp /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).img.bak


2      Now rebuild the initramfs for the current kernel version:

# dracut -f

Note:

If you are in a kernel version different to the initrd we are building (including if you are in Rescue Mode). We must specify the full kernel version, including architecture:


# dracut -f initramfs-2.6.32-71.el6.x86_64.img 2.6.32-71.el6.x86_64

The only purpose of an initramfs is to mount the root filesystem.

The initramfs is a complete set of directories that you would find on a normal root filesystem.

At boot time, the boot loader loads the kernel and the initramfs image into memory and starts the kernel. 

The kernel checks for the presence of the initramfs and, if found, mounts it as / and runs /init. 

The init program is typically a shell script. Note that the boot process takes longer, possibly significantly longer, if an initramfs is used.