banger/docs/advanced.md

Advanced flows

banger vm run covers the common sandbox case. This doc is for the rest: scripting, arbitrary images, custom rootfs stacks, long-lived guest processes.

vm create — the low-level primitive

Use when you want to provision without starting, or when you need to script VM creation piecewise.

banger vm create --image debian-bookworm --name testbox --no-start
banger vm start testbox
banger vm ssh testbox
banger vm stop testbox
banger vm delete testbox

vm create is synchronous by default, but on a TTY it shows live progress until the VM is fully ready.

image pull <oci-ref> — arbitrary container images

For images outside banger's catalog, pull from any OCI registry:

banger image pull docker.io/library/alpine:3.20 --kernel-ref generic-6.12

Layers are flattened, ownership is fixed (setuid binaries, root-owned config preserved), banger's guest agents are injected, and a first-boot systemd service installs openssh-server via the guest's package manager so the VM is reachable on first boot.

See docs/oci-import.md for supported distros, caveats, and the internal/imagepull design.

image register — existing host-side stack

If you already have an ext4 rootfs, a kernel, optional initrd, and optional modules as files on disk:

banger image register --name base \
  --rootfs /abs/path/rootfs.ext4 \
  --kernel-ref generic-6.12

You can mix --kernel-ref (a cataloged kernel) with --rootfs from disk, or pass --kernel /abs/path/vmlinux for a one-off kernel.

For reproducible custom images, write a Dockerfile and publish it to an image catalog. See docs/image-catalog.md.

Workspace + session primitives

Long-lived guest commands managed by the daemon, attachable over a local Unix socket bridge. Useful for agent/background processes that need to survive SSH disconnects.

banger vm workspace prepare <vm> ./other-repo --guest-path /root/repo
banger vm session start <vm> --name planner --cwd /root/repo \
  --stdin-mode pipe -- pi --mode rpc
banger vm session attach <vm> planner
banger vm session logs <vm> planner --stream stderr
banger vm session stop <vm> planner

Details:

• vm workspace prepare materialises a local git checkout into a running VM. Default guest path /root/repo; default mode is a shallow metadata copy plus tracked and untracked non-ignored overlay.
• vm session start launches a daemon-managed long-lived guest command. The daemon preflights that the guest cwd exists and the command is on guest PATH before launch. Use --stdin-mode pipe when you need live attach.
• vm session attach is exclusive and same-host only. Pipe-mode sessions survive daemon restarts.

Inspecting boot failures

When a VM's create flow errors ("ssh did not come up within 90s" or similar), the VM is kept alive for inspection:

• banger vm logs <name> — the firecracker serial console output, the best window into a stuck boot (systemd unit failures, kernel panics, missing modules).
• banger vm ports <name> — what's listening in the guest. Works as long as banger's vsock agent has come up, even if SSH is wedged.
• banger vm show <name> — daemon-side state (IP, PID, overlay paths).

--rm on vm run intentionally does NOT fire when the initial ssh wait times out, so the VM stays around for post-mortem.