buildroot: No rootfs in rootfs.iso9660 image file - buildroot

Question

I am trying to build my own USB Bootable Linux.
As far as I have understood the buildroot documentation, buildroot should give me ready-for-use images.
My output folder contains the following images:
build#build:~/buildroot_usb/output/images$ ls * -lh
-rw-r--r-- 1 root root 45M Sep 19 18:26 bzImage
-rw-r--r-- 1 root root 102M Sep 19 18:25 rootfs.cpio
-rw-r--r-- 1 root root 512M Sep 19 18:25 rootfs.ext2
lrwxrwxrwx 1 root root 11 Sep 19 18:25 rootfs.ext4 -> rootfs.ext2
-rw-r--r-- 1 root root 46M Sep 19 18:26 rootfs.iso9660
-rw-r--r-- 1 root root 111M Sep 19 18:26 rootfs.tar
-rw-r--r-- 1 root root 37M Sep 19 18:26 rootfs.tar.gz
syslinux:
insgesamt 164K
-rwxr-xr-x 1 root root 36K Sep 19 17:42 isolinux.bin
-rwxr-xr-x 1 root root 440 Sep 19 17:42 mbr.bin
-rwxr-xr-x 1 root root 124K Sep 19 17:42 syslinux.efi
build#build:~/buildroot_usb/output/images$
The rootfs.iso9600 image should be a Bootable ISO image. But the size of the file shows that the whole root file system is missing. it's only the kernel and the bootloader inside. (i checked that).
Config:

Answer 1

You have enabled to have the root filesystem as an initramfs inside the kernel image, so it gets compressed. If you look at your bzImage file (the kernel image), it's 45 MB, so it's definitely the kernel + the compressed root filesystem. Your ISO image is 46 MB, so it's basically just the kernel image + the bootloader, so it's all good.
Compare that to the size of the compressed rootfs tarball (rootfs.tar.gz), which is 37 MB in size. It all matches pretty well.
So, your 46 MB ISO image definitely contains the root filesystem, compressed as an initramfs inside the kernel image.