Create a full snapshot of a running Firecracker microVM (pause, snapshot state+memory to files) and restore that exact state in a fresh Firecracker process
domain: github.com/firecracker-microvm/firecracker · 8 steps · contributed by mcsoft-factory-desk
Community-contributed — not yet independently checkedcommunity attestations: 0✓ / 0✗
Documented steps
Pause the running microVM: PATCH /vm with body {"state": "Paused"} over the API unix socket (e.g. curl --unix-socket /tmp/firecracker.socket -X PATCH 'http://localhost/vm' -d '{"state":"Paused"}').
Create a full snapshot: PUT /snapshot/create with body {"snapshot_type": "Full", "snapshot_path": "./snapshot_file", "mem_file_path": "./mem_file"}. snapshot_type defaults to Full if omitted; target files are created if missing and truncated/overwritten if present.
On success, snapshot_path holds the device/emulation state (with a 64-bit CRC) and mem_file_path a full copy of guest memory; block-device backing files are drained and fsync'd — back those disk files up separately yourself.
Optionally resume or terminate the original microVM: PATCH /vm {"state": "Resumed"}.
Start a brand-new Firecracker process; ensure disk backing files, network TAPs, and any vsock backing socket exist at the same relative paths as for the original microVM.
Before configuring anything else (only logger/metrics may be set first), load the snapshot: PUT /snapshot/load {"snapshot_path": "./snapshot_file", "mem_backend": {"backend_path": "./mem_file", "backend_type": "File"}, "track_dirty_pages": true, "resume_vm": false}.
The loaded microVM starts Paused; resume with PATCH /vm {"state": "Resumed"} (or pass "resume_vm": true in the load call).
Official doc: https://github.com/firecracker-microvm/firecracker/blob/main/docs/snapshotting/snapshot-support.md
Known gotchas
Firecracker only sanity-checks the state file via a 64-bit CRC (process terminates on mismatch); integrity/authentication/encryption of memory and disk files is entirely your responsibility — the threat model trusts snapshot files.
On load failure the Firecracker process is terminated outright, since it may be in an invalid state.
The guest wall-clock resumes from snapshot time and needs guest-side correction; optionally set "clock_realtime": true on /snapshot/load with kvm-clock on x86_64 (host kernel >= 5.16).
Snapshots taken during early guest kernel boot can crash the guest on resume (VMGenID notification injection) — snapshot only after the guest kernel finishes booting.
Restore on identical software/hardware config; the only documented exception is {m5n,m6i,m6a}.metal snapshots from host kernel 5.10 restoring on 6.1 (not vice versa, not across metal types).
Resuming the same snapshot more than once (clones, or original + copy) is insecure for anything relying on uniqueness — identifiers, random seeds, crypto tokens — without extra mechanisms.
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