Kernels

A container image holds no kernel: containers share their host’s. A virtual machine needs one of its own, so every instance boots a kernel you choose, kept apart from its image.

Importing a kernel

A kernel is imported by name, from a URL, for an architecture:

$ dicer kernel import linux-6.18 --arch x86_64 \
    --url https://github.com/konradasb/dicer-kernel/releases/download/v6.18.53-1/vmlinux-x86_64 \
    --sha256 ca5db6c291deb8a409db1f1ab14cc55ef6d35504daf17fc0f5577ffc1662b669

Importing records the kernel; it is downloaded the first time an instance boots with it, and kept. With --sha256, the download is checked against it. A URL may also be a file:// URL or an absolute path on the host.

The kernel’s architecture must be the host’s: x86_64 or aarch64.

Kernel requirements

dicer-kernel publishes the kernel Dicer is tested with, for x86_64 and aarch64: a long-term Linux release from kernel.org, with Cloud Hypervisor’s configuration and what Dicer’s guests need on top. It boots under both hypervisors. Each release lists its checksums in a SHA256SUMS signed with cosign, and carries the kernel’s source and configuration.

A kernel of your own works too, if it has what Dicer’s guests rely on:

• EROFS, with compression, to mount the image;
• overlayfs, to lay the instance’s disk over it;
• virtio’s block, network and vsock devices, and virtio-mmio for Firecracker;
• a serial console.

The configuration dicer-kernel adds, in its dicer.config, is a good place to start.

Choosing a kernel

An instance names its kernel with --kernel. One that names none gets the daemon’s default: the kernel its configuration names, or, if there is exactly one kernel, that one. dicer info shows which applies.

Kernel arguments

An instance boots with the command line its hypervisor needs, such as console=ttyS0 reboot=k panic=1. --kernel-args replaces it whole, so keep those arguments when adding your own.

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