pcakerで`virtualbox-iso: sudo: sorry, you must have a tty to run sudo`が出る

packerでbuild時にvirtualbox-iso: sudo: sorry, you must have a tty to run sudoがでた時の備忘録です。

configファイルのbuildersセクションに以下を追加すると解決。

"ssh_pty" : "true"

以下利用しているbuildersセクション

  "builders":[{
    "type": "virtualbox-iso",
    "guest_os_type": "RedHat_64",
    "iso_url": "http://ftp.iij.ad.jp/pub/linux/centos/6.7/isos/x86_64/CentOS-6.7-x86_64-minimal.iso",
    "iso_checksum": "9381a24b8bee2fed0c26896141a64b69",
    "iso_checksum_type": "md5",
    "ssh_username": "vagrant",
    "ssh_password": "vagrant",
    "ssh_wait_timeout": "3000s",
    "vm_name": "box",
    "http_directory": "./",
    "boot_wait": "30s",
    "boot_command":[
      "<esc><wait>",
      "linux ks=http://{{ .HTTPIP }}:{{ .HTTPPort }}/ks.cfg ",
      "<enter><wait>"
    ],
    "shutdown_command": "echo 'vagrant' | sudo -S shutdown -P now",
    "ssh_pty" : "true"
  }],