Volumes

<Note> **Cloud:** Volumes use fast block storage managed by the platform. Every organization automatically gets an undeletable **host volume**: think of it as the disk of the one computer all its sandboxes run on, and it is what bind and disk-image mounts resolve against. </Note>

Volumes give a sandbox persistent or shared storage by mounting host data, managed storage, disk images, or in-memory filesystems into the guest. Mounts provide direct filesystem access and are significantly faster than the filesystem API, which transfers files individually, so they are preferable for anything beyond ad-hoc reads and writes.

microsandbox supports four mount types on both backends: bind mounts, named volumes, disk-image volumes, and tmpfs.

Cloud default volume

Every Cloud organization has an always-present default volume. You can read and write it directly without starting a sandbox:

<CodeGroup> ```rust Rust let volume = Volume::get_default().await?; volume.fs().write("state.json", br#"{"ready":true}"#).await?; ```

typescript

const volume = await Volume.getDefault();
await volume.fs().write("state.json", JSON.stringify({ ready: true }));

python

volume = await Volume.get_default()
await volume.fs().write("state.json", b'{"ready": true}')

volume, err := m.GetDefaultVolume(ctx)
err = volume.FS().WriteString("state.json", `{"ready":true}`)

</CodeGroup>

The default volume is isolated to the authenticated Cloud organization and cannot be removed. Default-volume lookup is deliberately unsupported on the local backend: forgetting an API key cannot expose or modify files from your machine. Named local volumes continue to live under ~/.microsandbox/volumes/ and retain their existing direct filesystem API.

Bind mounts

<Tooltip tip="The host path resolves against your organization's host volume, not the computer running the SDK or CLI.">On cloud <Icon icon="circle-info" size={11} /></Tooltip>

Mount a directory from the host directly into the sandbox. Changes inside the sandbox are reflected on the host, and vice versa.

<CodeGroup> ```rust Rust let sb = Sandbox::builder("dev") .image("python") .volume("/app/src", |v| v.bind("./src").readonly().noexec()) .volume("/app/data", |v| v.bind("./data")) .create() .await?; ```

typescript

import { Sandbox } from "microsandbox";

await using sb = await Sandbox.builder("dev")
    .image("python")
    .volume("/app/src",  (m) => m.bind("./src").readonly().noexec())
    .volume("/app/data", (m) => m.bind("./data"))
    .create();

python

from microsandbox import Sandbox, Volume

sb = await Sandbox.create(
    "dev",
    image="python",
    volumes={
        "/app/src": Volume.bind("./src", readonly=True, noexec=True),
        "/app/data": Volume.bind("./data"),
    },
)

sb, err := m.CreateSandbox(ctx, "dev",
    m.WithImage("python"),
    m.WithMounts(map[string]m.MountConfig{
        "/app/src":  m.Mount.Bind("./src", m.MountOptions{Readonly: true, Noexec: true}),
        "/app/data": m.Mount.Bind("./data", m.MountOptions{}),
    }),
)

bash

msb create python --name dev \
  --mount-dir ./src:/app/src:ro,noexec \
  --mount-dir ./data:/app/data

</CodeGroup>

Use --mount-file when you want to bind one host file instead of an entire directory.

bash

msb create alpine --name config-reader \
  --mount-file ./config.toml:/etc/app/config.toml:ro,nodev

Named volumes

<Tooltip tip="On microsandbox cloud, create named volumes before mounting them; create-on-mount, disk-kind volumes, and size are not available, and quota must be a whole number of GiB.">Limited on cloud <Icon icon="circle-info" size={11} /></Tooltip>

microsandbox manages named volumes and stores them by default under ~/.microsandbox/volumes/<name>/. They persist independently of any sandbox, so you can create a volume, populate it, and mount it into different sandboxes over time.

Named volumes can be directory-backed or disk-backed. Directory volumes mount through virtiofs. Disk volumes are raw ext4 disk images managed by microsandbox and mount through virtio-blk.

CLI named mounts are idempotent. -v name:/path and --mount-named name:/path create a directory-backed named volume if it does not already exist, then mount it. If the volume already exists, microsandbox reuses it when the requested storage settings are compatible and errors when they are not. Use --mount-named name:/path:kind=disk,size=20G to create or reuse a disk-backed named volume from the mount flag itself.

SDK named(...) mount helpers are existing-only. They fail if the named volume does not already exist. Use each SDK's explicit named-volume mode API when you want sandbox creation to create or ensure the volume.

Create a volume

<CodeGroup> ```rust Rust let cache = Volume::builder("pip-cache") .create() .await?; ```

typescript

import { Volume } from "microsandbox";

const cache = await Volume.builder("pip-cache").create();

python

cache = await Volume.create("pip-cache")

cache, err := m.CreateVolume(ctx, "pip-cache")

bash

msb volume create pip-cache

</CodeGroup>

Create a disk-backed named volume when a workload needs a real guest block filesystem, such as Docker's data root:

<CodeGroup> ```rust Rust let docker_data = Volume::builder("docker-data") .disk() .size(20.gib()) .create() .await?; ```

typescript

const dockerData = await Volume.builder("docker-data")
  .disk()
  .size(20 * 1024)
  .create();

python

from microsandbox import VolumeKind

docker_data = await Volume.create(
    "docker-data",
    kind=VolumeKind.DISK,
    size_mib=20 * 1024,
)

dockerData, err := m.CreateVolume(ctx, "docker-data",
    m.WithVolumeKind(m.VolumeKindDisk),
    m.WithVolumeSize(20 * 1024),
)

bash

msb volume create docker-data --kind disk --size 20G

</CodeGroup>

Mount in a sandbox

<CodeGroup> ```rust Rust let sb = Sandbox::builder("worker") .image("python") .volume("/root/.cache/pip", |v| v.named(cache.name())) .create() .await?; ```

typescript

await using sb = await Sandbox.builder("worker")
    .image("python")
    .volume("/root/.cache/pip", (m) => m.named(cache.name))
    .create();

python

sb = await Sandbox.create(
    "worker",
    image="python",
    volumes={
        "/root/.cache/pip": Volume.named(cache.name),
    },
)

sb, err := m.CreateSandbox(ctx, "worker",
    m.WithImage("python"),
    m.WithMounts(map[string]m.MountConfig{
        "/root/.cache/pip": m.Mount.Named(cache.Name(), m.MountOptions{}),
    }),
)

bash

msb create python --name worker \
  --mount-named pip-cache:/root/.cache/pip

</CodeGroup>

The CLI command above creates pip-cache as a directory-backed named volume if it is missing. To create or reuse a disk-backed named volume while mounting it:

bash

msb create docker:dind --name docker-demo \
  --mount-named docker-data:/var/lib/docker:kind=disk,size=20G

<Tooltip tip="Host-side access to an unmounted volume is not available on microsandbox cloud; mount the volume into a sandbox and use the sandbox filesystem instead.">Limited on cloud <Icon icon="circle-info" size={11} /></Tooltip>

Mount the same directory-backed named volume into multiple sandboxes when they need to share files. Use readonly on consumers that should not write. Disk-backed named volumes are attached as block devices; use one writable sandbox at a time, or read-only mounts where sharing is intended.

Directory-backed named volumes are also accessible from the host without a running sandbox, so you can pre-populate a cache or inspect output after the sandbox stops. Disk-backed named volumes store guest data inside disk.raw; host filesystem helpers operate on the managed volume directory, not the filesystem inside the disk image.

Manage volumes

<CodeGroup> ```rust Rust let volumes = Volume::list().await?; Volume::remove("old-cache").await?; ```

typescript

const volumes = await Volume.list();
await Volume.remove("old-cache");

python

volumes = await Volume.list()
await Volume.remove("old-cache")

volumes, err := m.ListVolumes(ctx)
err = m.RemoveVolume(ctx, "old-cache")

bash

msb volume ls
msb volume rm old-cache

</CodeGroup>

Disk-image volumes

Disk-image volumes attach a host disk image as a virtio-blk device and mount its inner filesystem at a guest path. Use them when you want persistent state isolated from ordinary host filesystem metadata, or when distributing a prebuilt filesystem image. The disk format defaults from the file extension (.qcow2, .raw, .vmdk; otherwise raw), and the inner filesystem type is auto-detected unless you set fstype.

<CodeGroup> ```rust Rust let sb = Sandbox::builder("seeded") .image("alpine") .volume("/seed", |v| v.disk("./seed.raw").readonly().noexec()) .create() .await?; ```

typescript

await using sb = await Sandbox.builder("seeded")
    .image("alpine")
    .volume("/seed", (m) => m.disk("./seed.raw").readonly().noexec())
    .create();

python

sb = await Sandbox.create(
    "seeded",
    image="alpine",
    volumes={"/seed": Volume.disk("./seed.raw", readonly=True, noexec=True)},
)

sb, err := m.CreateSandbox(ctx, "seeded",
    m.WithImage("alpine"),
    m.WithMounts(map[string]m.MountConfig{
        "/seed": m.Mount.Disk("./seed.raw", m.DiskOptions{Readonly: true, Noexec: true}),
    }),
)

bash

msb create alpine --name seeded \
  --mount-disk ./seed.raw:/seed:ro,noexec,fstype=ext4

</CodeGroup>

Tmpfs

An in-memory filesystem that disappears when the sandbox stops. Useful for scratch space, build artifacts, or anything that doesn't need to outlive the sandbox.

<CodeGroup> ```rust Rust let sb = Sandbox::builder("worker") .image("alpine") .volume("/tmp/scratch", |v| v.tmpfs().size(100).noexec()) .create() .await?; ```

typescript

import { Sandbox } from "microsandbox";

await using sb = await Sandbox.builder("worker")
    .image("alpine")
    .volume("/tmp/scratch", (m) => m.tmpfs().size(100).noexec())
    .create();

python

sb = await Sandbox.create(
    "worker",
    image="alpine",
    volumes={
        "/tmp/scratch": Volume.tmpfs(size_mib=100, noexec=True),
    },
)

sb, err := m.CreateSandbox(ctx, "worker",
    m.WithImage("alpine"),
    m.WithMounts(map[string]m.MountConfig{
        "/tmp/scratch": m.Mount.Tmpfs(m.TmpfsOptions{SizeMiB: 100, Noexec: true}),
    }),
)

bash

msb create alpine --name worker \
  --tmpfs /tmp/scratch:100:noexec

</CodeGroup>

Mount options

Mounts use normal Linux behavior by default: writable, executable, suid-enabled, and device-enabled. Adjust with:

readonly / ro when the guest should not write to the mount.
noexec when files on the mount should not be executed directly.
nosuid when setuid/setgid bits should be ignored.
nodev when device files should be ignored.

noexec does not stop interpreters from reading scripts from the mount, for example sh /app/src/script.sh.

For stronger in-guest hardening, create the sandbox with the restricted security profile. Restricted sandboxes set no_new_privs, drop mount-admin capability from user commands, and force nosuid,nodev on user mounts. This profile is incompatible with workloads such as sudo and Docker-in-Docker.

CLI syntax and flags

CLI mount flags use SOURCE:DEST[:OPTIONS]. The : before OPTIONS starts the option block, and commas separate options inside that block.

Flag	Source	Options
`--mount-dir`	Host directory	`ro`, `rw`, `noexec`, `nosuid`, `nodev`, `stat-virt=strict\|relaxed\|off`, `host-perms=private\|mirror`
`--mount-file`	Host file	`ro`, `rw`, `noexec`, `nosuid`, `nodev`, `stat-virt=strict\|relaxed\|off`, `host-perms=private\|mirror`
`--mount-named`	Named volume	`ro`, `rw`, `noexec`, `nosuid`, `nodev`, `kind=dir\|disk`, `size=<size>` for `kind=disk`, `quota=<size>` for directory volumes; directory-backed named volumes also support `stat-virt=strict\|relaxed\|off`, `host-perms=private\|mirror`
`--mount-disk`	Host disk image	`ro`, `rw`, `noexec`, `nosuid`, `nodev`, `format=raw\|qcow2\|vmdk`, `fstype=<type>`
`--tmpfs`	Guest path	`ro`, `rw`, `noexec`, `nosuid`, `nodev`; size may be passed as `PATH:SIZE[:OPTIONS]`

Combining mounts

Mount flags may be repeated, so a sandbox can combine host directories, individual files, named volumes, disk images, and tmpfs scratch space.

<CodeGroup> ```rust Rust let sb = Sandbox::builder("full") .image("python") .volume("/app/src", |v| v.bind("./src").readonly().noexec()) .volume("/app/pyproject.toml", |v| v.bind("./pyproject.toml").readonly()) .volume("/root/.cache/pip", |v| { v.named("pip-cache") .stat_virtualization(StatVirtualization::Relaxed) }) .volume("/dataset", |v| { v.disk("./dataset.qcow2") .format(DiskImageFormat::Qcow2) .fstype("ext4") .readonly() }) .volume("/tmp", |v| v.tmpfs().size(1024).noexec().nosuid().nodev()) .create() .await?; ```

bash

msb create python --name full \
  --mount-dir ./src:/app/src:ro,noexec \
  --mount-file ./pyproject.toml:/app/pyproject.toml:ro \
  --mount-named pip-cache:/root/.cache/pip:stat-virt=relaxed \
  --mount-disk ./dataset.qcow2:/dataset:ro,format=qcow2,fstype=ext4 \
  --tmpfs /tmp:1G:noexec,nosuid,nodev

</CodeGroup>

Cloud default volume

Bind mounts

Named volumes

Create a volume

Mount in a sandbox

Sharing and host-side access

Manage volumes

Disk-image volumes

Tmpfs

Mount options

CLI syntax and flags

Combining mounts