default TARGET_OS var

[LynnOS]

HI,all
I find the default TARGET_OS var is in conf/bitbake

TARGET_OS = "INVAILD"

but in local.conf,it says:

# Use this to specify the target operating system.  The default is "linux",
# for a normal linux system with glibc. Set this to "linux-uclibc" if you want
# to build a uclibc based system.
# Normally the DISTRO of your choosing will take care of this
# TARGET_OS = "linux"

Where defines TARGET_OS default var? conf/bitbake.conf ? it sets
TARGET_OS to invalid

thanks for help


Lynnos