Snapshots

A snapshot is a portable, on-disk capture of a sandbox’s writable filesystem. Move it with scp, archive it as .tar.zst, or boot fresh sandboxes from it.

Snapshots are disk-only and require a sandbox that is not running. You can snapshot stopped and crashed sandboxes; microsandbox rejects running, draining, and paused sandboxes.

What gets captured

Captured	Not captured
Writable filesystem changes	Memory contents
Pinned image identity	Running processes
Optional labels and integrity hash	Network state

Booting from a snapshot is a cold boot of a fresh VM that starts from the captured filesystem changes.

Quick start

You’ll usually reach for the CLI first:

# 1. Boot a sandbox, install state, then stop it
msb run --name baseline --detach python:3.12
msb exec baseline -- pip install requests
msb stop baseline

# 2. Snapshot the stopped sandbox
msb snapshot create after-pip-install --from baseline

# 3. Boot a fresh sandbox from the snapshot
msb run --name worker --from-snapshot after-pip-install \
    -- python -c "import requests; print(requests.__version__)"

By default, the snapshot lives at ~/.microsandbox/snapshots/after-pip-install/. That whole directory is the snapshot.

Snapshot a sandbox

Snapshot under a bare name, resolved to ~/.microsandbox/snapshots/<name>/ by default. The name is the snapshot’s identity; pass a destination directory to create the artifact on a different volume (DIR/<name>). Either way the directory is the whole artifact; move it with save/load (or plain mv):

import { Sandbox } from "microsandbox";

const h = await Sandbox.get("baseline");

// Resolves under ~/.microsandbox/snapshots/<name>/
const snap = await h.snapshot("after-pip-install");

console.log(snap.digest); // sha256:...

use microsandbox::Sandbox;

let h = Sandbox::get("baseline").await?;

// Resolves under ~/.microsandbox/snapshots/<name>/
let snap = h.snapshot("after-pip-install").await?;

println!("{}", snap.digest()); // sha256:...

from microsandbox import Sandbox

h = await Sandbox.get("baseline")

# Resolves under ~/.microsandbox/snapshots/<name>/
snap = await h.snapshot("after-pip-install")

print(snap.digest)  # sha256:...

h, err := m.GetSandbox(ctx, "baseline")
if err != nil {
    return err
}

// Resolves under ~/.microsandbox/snapshots/<name>/
snap, err := h.Snapshot(ctx, "after-pip-install")

fmt.Println(snap.Digest()) // sha256:...

msb snapshot create after-pip-install --from baseline
msb snapshot create after-pip-install --from baseline --label stage=ready

# Create the artifact on another volume: lands at /mnt/big/after-pip-install
msb snapshot create after-pip-install --from baseline --dest-dir /mnt/big

The sandbox must be stopped or crashed; microsandbox rejects running sandboxes.

Boot from a snapshot

A snapshot already pins its image, so booting from one is mutually exclusive with the image source:

import { Sandbox } from "microsandbox";

const sb = await Sandbox.builder("worker")
    .fromSnapshot("after-pip-install")
    .create();

use microsandbox::Sandbox;

let sb = Sandbox::builder("worker")
    .from_snapshot("after-pip-install")
    .create()
    .await?;

from microsandbox import Sandbox

# `from_snapshot=` is a peer of `image=` and mutually exclusive with it
sb = await Sandbox.create("worker", from_snapshot="after-pip-install")

sb, err := m.CreateSandbox(ctx, "worker",
    m.WithFromSnapshot("after-pip-install"),
)

msb run --name worker --from-snapshot after-pip-install -- python -V

Booting validates the snapshot, resolves the pinned image, and gives the new sandbox its own writable copy.

List, inspect, and remove

import { Snapshot } from "microsandbox";

const all = await Snapshot.list();                       // Indexed snapshots
const h = await Snapshot.get("after-pip-install");       // By name, digest, or path
console.log(`${h.name ?? "-"} (${h.digest})`);

await Snapshot.remove("after-pip-install");
await Snapshot.reindex();                               // Default snapshots directory

use microsandbox::Snapshot;

let all = Snapshot::list().await?; // Indexed snapshots
let h = Snapshot::get("after-pip-install").await?; // By name, digest, or path
println!("{} ({})", h.name().unwrap_or("-"), h.digest());

Snapshot::remove("after-pip-install", false).await?;
Snapshot::reindex("/data/snapshots").await?;

from microsandbox import Snapshot

all = await Snapshot.list()                              # Indexed snapshots
h = await Snapshot.get("after-pip-install")              # By name, digest, or path
print(f"{h.name or '-'} ({h.digest})")

await Snapshot.remove("after-pip-install")
await Snapshot.reindex()                                 # Default snapshots directory

all, err := m.Snapshot.List(ctx)            // Indexed snapshots
fmt.Printf("%d snapshots\n", len(all))
h, err := m.Snapshot.Get(ctx, "after-pip-install") // By name, digest, or path
name := "-"
if h.Name() != nil {
    name = *h.Name()
}
fmt.Printf("%s (%s)\n", name, h.Digest())

err = m.Snapshot.Remove(ctx, "after-pip-install", false)
_, err = m.Snapshot.Reindex(ctx, "/data/snapshots")

msb snapshots                  # Also: msb snaps, msb snapshot ls
msb snapshot inspect after-pip-install
msb snapshot rm after-pip-install

# Also if it has indexed children
msb snapshot rm after-pip-install --force

# Rebuild the index from artifacts on disk
msb snapshot reindex

list and get use a local index for fast lookup. If the index gets out of sync, reindex rebuilds it from the snapshot artifacts on disk.

Move snapshots between machines

The snapshot directory is the whole artifact; there is no hidden daemon state. Copy the directory directly, or save it as an archive:

# Copy the directory directly with scp (image must be cached or pullable on the target)
scp -r ~/.microsandbox/snapshots/after-pip-install \
    other-host:~/.microsandbox/snapshots/

# Bundle into a .tar.zst, transport, then load
msb snapshot save after-pip-install /tmp/snap.tar.zst
scp /tmp/snap.tar.zst other-host:
ssh other-host msb snapshot load /tmp/snap.tar.zst

# Fully offline: include the OCI image cache so the target needs no network
msb snapshot save after-pip-install /tmp/snap.tar.zst --with-image
ssh other-host msb snapshot load /tmp/snap.tar.zst

Archives default to .tar.zst. Pass --plain-tar for a plain .tar. SDKs expose the same save and load operations as the CLI.

Integrity verification

By default, snapshot creation records structural metadata without hashing the writable layer. Opt in when you need a persistent content check. Current snapshots use a fixed 64 KiB-leaf BLAKE3 Merkle tree: known sparse holes collapse into precomputed zero subtrees, while allocated bytes are read and hashed.

import { Snapshot } from "microsandbox";

// Compute and record an integrity hash at create time
const snap = await Snapshot.builder("after-pip-install")
  .fromSandbox("baseline")
  .recordIntegrity()
  .create();

// Verify a snapshot's recorded integrity on demand
const report = await snap.verify();

use microsandbox::Snapshot;

// Compute and record an integrity hash at create time
let snap = Snapshot::builder("after-pip-install")
    .from_sandbox("baseline")
    .record_integrity()
    .create()
    .await?;

// Verify a snapshot's recorded integrity on demand
let report = snap.verify().await?;

from microsandbox import Snapshot

# Compute and record an integrity hash at create time
snap = await Snapshot.create(
    "after-pip-install",
    from_sandbox="baseline",
    record_integrity=True,
)

# Verify a snapshot's recorded integrity on demand
report = await snap.verify()

// Compute and record an integrity hash at create time
snap, err := m.Snapshot.Create(ctx,
    m.SnapshotCreateOptions{
        Name:            "after-pip-install",
        FromSandbox:     "baseline",
        RecordIntegrity: true,
    },
)

// Verify a snapshot's recorded integrity on demand
report, err := snap.Verify(ctx)

# Compute and record an integrity hash at create time
msb snapshot create after-pip-install --from baseline --integrity

# Verify a snapshot's recorded integrity on demand
msb snapshot verify after-pip-install
msb snapshot inspect after-pip-install --verify

msb snapshot save and msb snapshot load preserve recorded integrity but do not silently execute it. They still enforce the archive grammar, path confinement, entry sizes, descriptor identities, and ordinary archive-entry hashes. Run msb snapshot verify explicitly after receiving a snapshot when your workflow requires an independent payload scan. Released msb-sparse-sha256-v1 descriptors remain readable and verifiable, but ordinary open, boot, save, load, and upgrade paths do not pay their full logical-size SHA cost.

Use cases

Reusable build state. Install dependencies once, snapshot, then msb run --from-snapshot ... repeatedly without paying the install cost. Common pattern for CI, agent workloads, and reproducible dev environments.
Portable scratch state. Capture a sandbox after a long setup, hand the artifact to a teammate or push it to shared storage, and let them boot from the same starting point.
Local fork-by-copy. Multiple sandboxes from one snapshot are independent; each copy of the upper layer diverges on its own.
Disaster recovery. Snapshot a sandbox before a risky migration; if it goes wrong, msb rm the broken one and msb run --from-snapshot from the pre-migration artifact.

Getting Started

Sandboxes

Networking

Operations

Troubleshooting

What gets captured

Quick start

Snapshot a sandbox

Boot from a snapshot

List, inspect, and remove

Move snapshots between machines

Integrity verification

Use cases

​What gets captured

​Quick start

​Snapshot a sandbox

​Boot from a snapshot

​List, inspect, and remove

​Move snapshots between machines

​Integrity verification

​Use cases

What gets captured

Quick start

Snapshot a sandbox

Boot from a snapshot

List, inspect, and remove

Move snapshots between machines

Integrity verification

Use cases