Source code of Ubuntu in Jetpack

Where do I find source code of Ubuntu delivered in Jetpack for Jetson Tx2 for customization purpose? and also will it be possible to gt source code of Jetpack package?

I don’t know about the R27.0.1 which the JTX1 ships with, but the R27.1 is here:
https://developer.nvidia.com/embedded/linux-tegra

There is a “Sources” link in the “Source Packages” listing which might have what you want. The drivers which are specific to the Jetson (direct hardware access…not part of the sample rootfs) are part of the driver package and don’t ship with source, e.g., the GPU driver for CUDA or video use isn’t public. During a command line flash using the driver package with sample rootfs it is the “apply_binaries.sh” step which adds those files which are not open source…the sample rootfs is purely Ubuntu.