This info take from http://www.voiceie.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=2;t=000238

• Boot CentOS and use linux rescue and chroot to the CCM drive.
• Add a user superuser

chroot /mnt/sysimage
chattr -i /etc/passwd /etc/group /etc/shadow /etc/gshadow
useradd -g root -G root,wheel -s /bin/bash superuser
passwd superuser

• edit /etc/passwd and give root the shell /bin/bash (replace /sbin/nologin with /bin/bash) (needed to su)
• edit /etc/pam.d/su and comment the line:

# auth required /lib/security/$ISA/pam_wheel.so group=priviledged_grp

• uncomment the line:

auth sufficient /lib/security/$ISA/pam_wheel.so trust use_uid