Initial ramdisk used mostly only to mount root filesystem.

Check available kernels (Example: section):

# geninitrd 

Regenerate (adding -v to see details) as suggested in above examples:

/sbin/geninitrd -f --initrdfs=initramfs /boot/initrd-KERVER.gz KERVER

Getting shell just after initrd boot ends/fails: Edit /etc/sysconfig/system , set:

RUN_SULOGIN_ON_ERR=no

Add

debugrd=sh 

to kernel boot options (by editing /boot/grub/grub.cfg or adding to GRUB_CMDLINE_LINUX_DEFAULT in /etc/sysconfig/grub and running update-grub)

Reboot. HINT: CTRL+PgUp/PgDown scrolls initrd logs.

Uncompressing initrd, copy first, ungzip, uncpio:

cp /boot/initrd.*.gz  /root/geninitrd
gunzip  initrd-4.1.15-1.gz
cpio -idmv < initrd-4.1.15-1

or have lesspipe, file installed and use less:

# less /boot/initrd-2.6.38.8-1.gz