Serial console in RHEL 6

There are changes between RHEL5 and RHEL6 about how to setup serial console. In RHEL 6 you no longer specify it in /etc/inittab, but leave it on upstart daemon work.

1. If you DONT WANT to have serial console as your default console:

# cat /boot/grub/menu.lst
default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
serial --unit=0 --speed=9600 --word=8 --parity=no --stop=1
terminal --timeout=10 serial console
hiddenmenu
title Red Hat Enterprise Linux (2.6.32-131.0.15.el6.x86_64)
 root (hd0,0)
 kernel /vmlinuz-2.6.32-131.0.15.el6.x86_64 ro root=/dev/mapper/rootvg-rootvol rd_LVM_LV=rootvg/rootvol rd_LVM_LV=rootvg/swapvol rd_NO_LUKS rd_NO_MD rd_NO_DM LANG=en_US.UTF-8 SYSFONT=latarcyrheb-sun16 KEYBOARDTYPE=pc KEYTABLE=us crashkernel=auto quiet console=ttyS0,9600n8 console=tty0
 initrd /initramfs-2.6.32-131.0.15.el6.x86_64.img

# grep ttyS0 /etc/securetty 
ttyS0

# cat /etc/init/ttyS0.conf
start on runlevel [345]
stop on runlevel [S016]

respawn
instance /dev/ttyS0
exec /sbin/agetty ttyS0 9600 vt100-nav

And initialize console with:

# initctl start ttyS0

2. If you DO WANT to have serial console as default console:

Add serial and terminal lines to menu.lst as above plus append "console=tty0 console=ttyS0,9600" to kernel line in /boot/grub/menu.lst

Thats all, as upstart will automatically start serial login process on last specified console parameter extracted from kernel line (in this case ttyS0).