unlock bootloader for lg optimus g (ls970) topic

hi, i am trying to install cyanogenmod on this fone using these instructions:
http://wiki.cyanogenmod.org/w/Install_CM_for_ls970

but this command is not working:

Code:

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[root@localhost ~]# adb devices
List of devices attached
LG-LS970-91d38109        device

[root@localhost ~]# adb reboot bootloader

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instead of going into the bootloader screen, it reboots the fone back into the android.

i enabled 'developer options' in the menu is there something else that is needed ?