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Linux kernel boot process

During boot process, the system will read the grub config to be able to load the kernel with it associated modules containing into initrd.

Initial RAM disk (initrd or Initramfs) is a RAM filesystem mounted at startup to initialize kernel modules.

Initrd

Rebuild initrd

# dracut -f

Regenerating the initramfs

Adding Drivers Because of Hardware Changes
Moving System Directories to a RAID or LVM
Adding Disks to an LVM Group or Btrfs RAID Containing the Root File System
Changing Kernel Variables (sysctl)
Adding or removing swap devices, re-creating swap area, it required also to recreate grub

You can read the content of initrd

# lsinitramfs /boot/initrd.img

Uncompress initrd

# mkdir /tmp/initrd
# cd /tmp/initrd
# cp /boot/initrd.img .
# unmkinitramfs initrd.img .

Generate a new grub.cfg

# grub2-mkconfig -o /boot/grub2/grub.cfg

Check the syntax of grub.cfg

# grub2-script-check /boot/grub2/grub.cfg