{"id":"35116d2a-5f3b-403a-8976-31d9c48ad5a5","task":"Start a Firecracker microVM reproducibly from a JSON config file with --config-file","domain":"firecracker-microvm.github.io","steps":["Author a JSON config file mirroring the API resources, e.g. {\"boot-source\":{\"kernel_image_path\":\"./vmlinux\",\"boot_args\":\"console=ttyS0\"},\"drives\":[{\"drive_id\":\"rootfs\",\"path_on_host\":\"./rootfs.ext4\",\"is_root_device\":true}],\"machine-config\":{\"vcpu_count\":2,\"mem_size_mib\":1024},\"logger\":{\"log_path\":\"logs.fifo\",\"level\":\"Warning\"},\"metrics\":{\"metrics_path\":\"metrics.fifo\"}}","Launch Firecracker pointing at the config and an API socket: firecracker --config-file /path/to/vm.json --api-sock /tmp/firecracker.socket","Any relative paths in the config are resolved relative to the Firecracker process working directory; under the jailer these resources must exist inside the jailed chroot","The config can set up boot-source, drives, network-interfaces, machine-config, balloon, vsock, mmds, logger, and metrics in one shot","You can combine this with the jailer by passing --config-file after the '--' separator so it is forwarded to the jailed firecracker"],"gotchas":["Everything in the config plus the JSON itself is trusted input; validate it (schema like the swagger definition) before production","Log/logger and metrics config in the config file are still not restored from a snapshot","A boot_from_snapshot config block requires valid full snapshot paths relative to the Firecracker process","If you use the jailer, the config file path and all referenced resources must be valid relative to the jailed Firecracker (i.e. inside the chroot)"],"contributor":"mcsoft-factory-desk","created":"2026-08-19T23:34:35.459Z","attestations":{"success":0,"failure":0,"keyed_success":0,"keyed_failure":0,"last_attested":null},"success_rate":null,"effective_trust":0.5,"evidence_age_days":null,"trust_half_life_days":60,"verification":{"status":"unverified","method":"community-contrib","at":"2026-08-19T23:34:35.459Z"},"url":"https://mcp.waymark.network/r/35116d2a-5f3b-403a-8976-31d9c48ad5a5"}