Unwanted (VDI) present

Recently I was given a task to run a outdated piece of commercial software on a very outdated (in)famous operating system. Unlucky for me on the given VDI (VirtualBox disk image) the so-called “Guests Additions” that enabled “better” time synchronization were already installed.

Fighting VBox time

So, this is what I had to do to keep the old clock:

• turn off networking card in the virtual machine configuration, because we do not want the system to use NTP or other newt service to get the “new” time,
• disable getting the host’s clock time: VBoxManage setextradata "WinXP" "VBoxInternal/Devices/VMMDev/0/Config/GetHostTimeDisabled" 1,
• and… this magic: VBoxManage modifyvm "WinXP" --biossystemtimeoffset "-341597644449", this thing does the very weird thing of telling the virtual machine BIOS how much to set it back in time, the offset here is total milliseconds between some old date and current date.

Getting the old date

With the Python script snippet below you will get the milliseconds to set back the VirtualBox clock to 01.01.2012 01:00.

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from datetime import datetime

round((datetime.strptime("01.01.2012 01:00", "%d.%m.%Y %H:%M")
      - datetime.now()).total_seconds() * 1000)

System preparation

Qemu

Emerge qemu with static-user USE enabled and your wanted architectures.

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app-emulation/qemu      QEMU_SOFTMMU_TARGETS: aarch64 arm x86_64
app-emulation/qemu      QEMU_USER_TARGETS: aarch64 arm x86_64

app-emulation/qemu      static-user
dev-libs/glib           static-libs
sys-apps/attr           static-libs
sys-libs/zlib           static-libs
dev-libs/libpcre2       static-libs

OpenRC

Enable qemu-binfmt:

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rc-update add qemu-binfmt default

Start qemu-binfmt:

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rc-service qemu-binfmt start

Chrooting

• select chroot location (eg /chroots/gentoo-arm64-musl-stable)
• unpack the desired rootfs
• create needed directories
  • mkdir -p /chroots/gentoo-arm64-musl-stable/var/cache/distfiles
• execute bwrap
  • with last ro-bind mount the qemu emulator binary (eg qemu-aarch64)
  • execute the mounted emulator binary giving it a shell program (eg bash)

Chroot with bwrap:

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bwrap                                                       \
    --bind /chroots/gentoo-arm64-musl-stable /              \
    --dev /dev                                              \
    --proc /proc                                            \
    --perms 1777 --tmpfs /dev/shm                           \
    --tmpfs /run                                            \
    --ro-bind /etc/resolv.conf /etc/resolv.conf             \
    --bind /var/cache/distfiles /var/cache/distfiles        \
    --ro-bind /usr/bin/qemu-aarch64 /usr/bin/qemu-aarch64   \
    /usr/bin/qemu-aarch64 /bin/bash -l

User-mode

By default you would probably have something like this, the user-mode network:

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<interface type="user">
  <mac address="00:00:00:00:00:00"/>
  <model type="virtio"/>
  <address type="pci" domain="0x0000" bus="0x01" slot="0x00" function="0x0"/>
</interface>

Bridge

Bridges can be easily created using the NetworkManager’s TUI tool called nmtui.

Bridge XML configuration for Libvirt

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<interface type="bridge">
  <mac address="00:00:00:00:00:00"/>
  <source bridge="br1"/>
  <target dev="vnet2"/>
  <model type="virtio"/>
  <alias name="net0"/>
  <address type="pci" domain="0x0000" bus="0x06" slot="0x00" function="0x0"/>
</interface>

Sysctl options

Be sure the following options are enabled (1):

• net.ipv4.ip_forward
• net.ipv4.conf.all.send_redirects

and the following options are disabled (0):

• net.bridge.bridge-nf-call-iptables