centos.json

{
    "builders": [
        {
            "type": "qemu",
            "accelerator": "kvm",
            "communicator": "ssh",
            "headless": true,
            "disk_image": false,
            "cpus": "6",
            "memory": "16384",
            "format": "raw",
            "iso_checksum": "none",
            "iso_url": "/dev/vdb",
            "skip_resize_disk": false,
            "skip_compaction": false,
            "disk_size": "40000M",
            "qemuargs": [
                ["-machine","pc-q35-4.2,accel=kvm,usb=off,vmport=off,dump-guest-core=off"],
                ["-cpu", "host"],
                [ "-smp", "cpus=4,sockets=1" ],
                [ "-cdrom", "cidata.iso" ],
                ["-drive", "file=/dev/vdb"]
            ],
            "ssh_username": "user",
            "ssh_password": "packer",
            "net_device": "virtio-net",
            "shutdown_command": "sudo shutdown --poweroff --no-wall now"
        }
    ],
    "provisioners": [
        {
            "type": "shell",
            "execute_command": "{{.Vars}} sudo -S -E bash '{{.Path}}'",
            "inline": [
                "yum update -y",
                "yum upgrade -y",
                "yum clean all -y"
            ]
        }
    ]
}