serial console

# vi /etc/inittab

co:12345:respawn:/sbin/agetty ttySx 115200

# vi /etc/grub.conf

#splashimage=(hd0,0)/grub/splash.xpm.gz
kernel /vmlinuz-xxx ro root=xxx rhgb quie console=tty0 console=ttySx,115200

# vi /etc/securetty

ttySx

cf. GRUB manual

7 Using GRUB via a serial line

cf. remote serial console howto