Building bare metal images with Packer, VirtualBox and qemu-img
This repository should demonstrate that it is possible to provision OS with Packer, then create raw disk image that can be booted directly on bare metal.
I am using random Alpine Packer builder from the GitHub (thanks!) because of Alpine small size.
Firstly, run packer build packer_template.json to create VirtualBox OVA archive which contains disk and configuration files.
Then decompress OVA tar archive and convert VMDK to RAW:
$ cd output-virtualbox-iso
$ tar xvf alpine-clean-3.6.1.ova
$ qemu-img convert -f vmdk alpine-clean-3.6.1-disk001.vmdk -O raw alpine-clean-3.6.1.raw
Check that RAW file is actual disk file:
$ fdisk -l alpine-clean-3.6.1.raw
Disk alpine-clean-3.6.1.raw: 2 GiB, 2147483648 bytes, 4194304 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x1de52f32
Device Boot Start End Sectors Size Id Type
alpine-clean-3.6.1.raw1 * 2048 206847 204800 100M 83 Linux
alpine-clean-3.6.1.raw2 206848 1255423 1048576 512M 82 Linux swap / Solaris
alpine-clean-3.6.1.raw3 1255424 4194303 2938880 1.4G 83 Linux
Partition offset is 1255424 sectors * 512 bytes per sector, so if you want to mount it, you can use mount command with the appropriate offset:
$ mkdir /tmp/loop
$ sudo mount -o ro,loop,offset=642777088 alpine-clean-3.6.1.raw /tmp/loop
$ mount | grep alpine-clean-3.6.1.raw
alpine-clean-3.6.1.raw on /tmp/loop type ext4 (ro,relatime,data=ordered)
If you want to create bootable USB, make sure that your USB is not mounted. If mounted, use umount command.
$ lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
...
sda 8:0 0 477G 0 disk
├─sda1 8:1 0 512M 0 part /boot/efi
├─sda2 8:2 0 460.6G 0 part /
└─sda3 8:3 0 15.9G 0 part
sdb 8:16 1 7.3G 0 disk /media/user/ABCD-EFGH <--- our mounted USB stick
$ sudo umount /media/user/ABCD-EFGH
Finally, write raw disk to the USB memory stick
$ sudo dd if=./alpine-clean-3.6.1.raw of=/dev/sdb bs=4k
131072+0 records in
131072+0 records out
536870912 bytes (537 MB, 512 MiB) copied, 139.334 s, 3.9 MB/s
TODO:
- Shrink disk image using zerofree / other tools
- ?
- Profit
Sources:
https://major.io/2010/12/14/mounting-a-raw-partition-file-made-with-dd-or-dd_rescue-in-linux/
https://blog.filippo.io/converting-a-partition-image-to-a-bootable-disk-image/
https://wiki.hackzine.org/sysadmin/kvm-import-ova.html