tdowty@ubuntu:~/cfc510p/christian_devel/poky/build$ bitbake-getvar IMAGE_FSTYPES -r  secure-core-image-initramfs
WARNING: IMAGE_INSTALL:append += is not a recommended operator combination, please replace it.
#
# $IMAGE_FSTYPES [4 operations]
#   set /home/tdowty/cfc510p/christian_devel/poky/meta-cfc510/conf/machine/include/innoflight-cfc510-common.inc:9
#     "wic wic.gz wic.bmap"
#   set /home/tdowty/cfc510p/christian_devel/poky/meta/conf/documentation.conf:214
#     [doc] "Formats of root filesystem images that you want to have created."
#   set? /home/tdowty/cfc510p/christian_devel/poky/meta/conf/bitbake.conf:832
#     "tar.gz"
#   set /home/tdowty/cfc510p/christian_devel/poky/meta-secure-core/meta/recipes-core/images/secure-core-image-initramfs.bb:28
#     "${INITRAMFS_FSTYPES}"
# pre-expansion value:
#   "${INITRAMFS_FSTYPES}"
IMAGE_FSTYPES="cpio.gz"