import Ubuntu 16.04 image into cobbler

if you got this error when you import Ubuntu 16.04 server image into cobbler using cobbler import command,

received on stderr:
No signature matched in /var/www/cobbler/ks_mirror/Ubuntu-16.04-x86_64
!!! TASK FAILED !!!

then modify this file:/var/lib/cobbler/distro_signatures.json, add the follow contents under ‘wily’ section,

"xenial": {
    "signatures":["dists", ".disk"],
    "version_file":"Release|mini-info",
    "version_file_regex":"Codename: xenial|Ubuntu 16.04",
    "kernel_arch":"linux-headers-(.*)\\.deb",
    "kernel_arch_regex":null,
    "supported_arches":["i386","amd64"],
    "supported_repo_breeds":["apt"],
    "kernel_file":"linux(.*)",
    "initrd_file":"initrd(.*)\\.gz",
    "isolinux_ok":false,
    "default_kickstart":"/var/lib/cobbler/kickstarts/sample.seed",
    "kernel_options":"",
    "kernel_options_post":"",
    "boot_files":[]
   }