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Copy a Sailbox, or start a fleet of identical ones

Copy an existing Sailbox. The copy gets the original’s disk and its memory, so whatever was running continues in the copy.

Usage

Take a checkpoint, then start as many Sailboxes from it as you like:

CLI

sail box checkpoint <id> --name after-setup
sail box from-checkpoint <checkpoint-id> --name worker-1

A sleeping or paused Sailbox can be copied without waking it: checkpoint returns its existing checkpoint. Starting several copies from one checkpoint reuses the same checkpoint data, so only the first copy pays for it.

Fan out to many

Set up one Sailbox (install dependencies, warm caches, start servers), checkpoint it, and start every worker from that checkpoint instead of repeating the setup in each one. This is the fast path to a fleet for agent rollouts, parallel test shards, or grading many submissions at once.

Python

import asyncio

checkpoint = sb.checkpoint()

async def fan_out(n: int) -> list[sail.Sailbox]:
    results = await asyncio.gather(
        *(
            sail.Sailbox.from_checkpoint.aio(
                checkpoint.checkpoint_id,
                name=f"worker-{i}",
            )
            for i in range(n)
        ),
        return_exceptions=True,  # keep the copies that came up
    )
    return [r for r in results if isinstance(r, sail.Sailbox)]

children = asyncio.run(fan_out(32))

Start the copies concurrently, as above, to overlap the restores. Collect results per copy so one failed restore does not cost you the rest, and give each a distinct name. Each copy is a full Sailbox: it bills like one and runs until it sleeps or you terminate it, so clean up the fleet when the work is done.

What a copy gets

• The disk and the memory. Processes running in the original continue. A command started with exec stops in the copy, though its writes up to the checkpoint are kept. One started in the background keeps running. Start anything else the copy needs again.
• A new identity and new networking. Open TCP connections are reset, and the copy doesn’t inherit exposed ports. Expose the ones it should serve.

Checkpoints

A checkpoint is a durable snapshot with a name, an id, and an expiry. It lasts seven days unless you set a TTL. Set one when a checkpoint is a template you will keep using, so it does not expire while you still need it. Starting a copy from an expired checkpoint fails.

CLI

sail box checkpoint <id> --name template --ttl-seconds 2592000

Checkpoints also protect the original. Take one after important setup, such as installing packages or fetching data: if the machine under a Sailbox fails, Sail restores it from the most recent completed checkpoint and does not replay commands that ran before it.

Find and delete checkpoints

Checkpoints belong to your organization. Listing shows the ones a Sailbox can still be started from, newest first, and can narrow them by name, by the Sailbox they were taken from, or by app. Deleting a checkpoint stops new Sailboxes from starting from it. Sailboxes already started from it keep running.

CLI

sail checkpoint list --name template
sail checkpoint delete <checkpoint-id>

Start fresh from a checkpoint’s disk

A copy normally resumes the checkpoint’s memory. To get only its files, start the copy without memory. The new Sailbox boots fresh from the checkpoint’s disk: nothing that was running in the original runs in the copy, and nothing that was only in memory carries over. It still boots this way if Sail has to restore it before it takes a checkpoint of its own. Booting takes longer than resuming memory.

CLI

sail box from-checkpoint <checkpoint-id> --name worker-1 --no-restore-memory