> ## Documentation Index
> Fetch the complete documentation index at: https://docs.ns.rocks/llms.txt
> Use this file to discover all available pages before exploring further.

# Choose A Per-Template Kernel

> Understand default and FUSE-capable guest kernel lanes.

Nullspace currently has a default Firecracker guest kernel lane and an opt-in
FUSE-capable lane for shared volumes and bucket mounts. The Python SDK does not
yet expose `Template.with_kernel(...)`, so kernel choice is an environment lane,
not a per-template SDK method.

## Current lanes

| Lane         | Use it for                                 | Current selector                                                          |
| ------------ | ------------------------------------------ | ------------------------------------------------------------------------- |
| Default      | General machines and templates             | Runtime host `NULLSPACE_KERNEL_PATH` default                              |
| FUSE-enabled | Shared volumes, `s3fs`, `gcsfuse`, JuiceFS | Set `NULLSPACE_KERNEL_PATH` to `vmlinux.fuse` and use the matching rootfs |

For private beta, use a deployment lane whose host kernel and rootfs are both
FUSE-capable when you need shared volumes or bucket mounts. Until an explicit
SDK selector ships, do not document or call `Template.with_kernel(...)`.

## Kernel version

The default local download lane uses Firecracker `1.14.1` and attempts the
Firecracker Linux 5.10 guest kernel artifact for the host architecture. The FUSE
builder pins `NULLSPACE_FUSE_LINUX_VERSION=5.10.252` unless overridden.

Check the actual running guest when exact version matters:

```python theme={"theme":{"light":"one-light","dark":"one-dark-pro"}}
from nullspace import Machine

with Machine.create(template="base") as machine:
    print(machine.commands.run("uname -r", shell=True).stdout.strip())
```

On a runtime host, operators can inspect the configured artifact path:

```bash theme={"theme":{"light":"one-light","dark":"one-dark-pro"}}
echo "${NULLSPACE_KERNEL_PATH:-./.local/artifacts/vmlinux}"
test -f "${NULLSPACE_KERNEL_PATH:-./.local/artifacts/vmlinux}.config" \
  && grep '^CONFIG_FUSE_FS=' "${NULLSPACE_KERNEL_PATH}.config"
```

## Template compatibility

Snapshot-backed templates record kernel compatibility metadata. If a runtime
host cannot restore a template or snapshot safely because the kernel or
architecture differs, the request fails explicitly instead of silently creating
an incompatible machine.

Concepts: [Create](../concepts/create), [Resume](../concepts/resume). API
reference: [buildTemplate](../api-reference), [createMachine](../api-reference).