Setting the root password in an OpenEmbedded image

During development, often a blank root password is used for the embedded Linux target system.  However, when deploying an embedded Linux system, often there is a requirement to set the root password to something non-obvious.  One way to do this is boot the system, and change the password using the passwd command.  Then copy the password hash from the /etc/shadow file into the below line in your image recipe.

sed 's%^root:[^:]*:%root:password_hash_from_etc_shadow:%' \
< ${IMAGE_ROOTFS}/etc/shadow \
> ${IMAGE_ROOTFS}/etc/;\
mv ${IMAGE_ROOTFS}/etc/ ${IMAGE_ROOTFS}/etc/shadow ;"

The ROOTFS_POSTPROCESS_COMMAND is useful for simple modifications like this to the rootfs image.