SSH - Microsandbox — ContextQMD

SSH gives a sandbox a familiar interface without putting an SSH daemon inside the guest. microsandbox speaks SSH on the host side, then forwards shells, remote commands, and SFTP file operations into the sandbox.

Use it when you want existing SSH tools to work with a sandbox, or when you want SDK code to use SSH semantics while still going through microsandbox.

There are two ways to connect:

Native sessions use the built-in microsandbox SSH client. No host ssh binary, TCP listener, or authorized key is required, which makes it the quickest path for a shell from msb or SSH semantics from the SDK.
External clients serve the sandbox as an SSH server so standard tools such as ssh, sftp, and ProxyCommand can connect.

Native sessions

Native sessions keep the SSH protocol boundary but do not expose a listener.

CLI

bash

msb ssh devbox
msb ssh connect devbox

With no remote command, the CLI opens an interactive shell. With --, the remaining tokens become the SSH command string and run through the sandbox shell.

bash

msb ssh devbox -- uname -a
msb ssh devbox -- sh -lc "cd /app && npm test"

If a sandbox name collides with an SSH subcommand such as serve or authorize, use --name:

bash

msb ssh --name serve
msb ssh --name authorize -- uptime

SDK

<CodeGroup> ```rust Rust let sb = Sandbox::start("devbox").await?; let ssh = sb.ssh().connect().await?;

let output = ssh.exec("uname -a").await?; println!("{}", String::from_utf8_lossy(&output.stdout));

ssh.close().await?;


```typescript TypeScript
const sb = await Sandbox.start("devbox");
const ssh = await sb.ssh().connect();

const output = await ssh.exec("uname -a");
console.log(output.stdout.toString());

await ssh.close();

python

sb = await Sandbox.start("devbox")
ssh = await sb.ssh().connect()

output = await ssh.exec("uname -a")
print(output.stdout_text)

await ssh.close()

sb, err := m.StartSandbox(ctx, "devbox")
if err != nil {
    return err
}
defer sb.Close()

ssh, err := sb.SSH().Connect(ctx)
if err != nil {
    return err
}
defer ssh.Close(ctx)

output, err := ssh.Exec(ctx, "uname -a")
if err != nil {
    return err
}
fmt.Print(string(output.Stdout))

</CodeGroup>

Interactive attach

SDK clients can attach the local terminal to an SSH shell. This requires a real terminal.

<CodeGroup> ```rust Rust let code = sb .ssh() .connect_with(|ssh| ssh.term("xterm-256color")) .await? .attach() .await?; ```

typescript

const ssh = await sb.ssh().connect({ term: "xterm-256color" });
const code = await ssh.attach({ detachKeys: "ctrl-]" });

python

ssh = await sb.ssh().connect(term="xterm-256color")
code = await ssh.attach(detach_keys="ctrl-]")

ssh, err := sb.SSH().Connect(ctx, m.WithSSHTerm("xterm-256color"))
if err != nil {
    return err
}
code, err := ssh.Attach(ctx, m.WithSSHDetachKeys("ctrl-]"))

</CodeGroup>

SFTP

The native SSH client can open SFTP over the same SSH connection.

<CodeGroup> ```rust Rust let sftp = ssh.sftp().await?; sftp.write("/tmp/hello.txt", b"hello").await?; let data = sftp.read("/tmp/hello.txt").await?; sftp.close().await?; ```

typescript

const sftp = await ssh.sftp();
await sftp.write("/tmp/hello.txt", Buffer.from("hello"));
const data = await sftp.read("/tmp/hello.txt");
await sftp.close();

python

sftp = await ssh.sftp()
await sftp.write("/tmp/hello.txt", b"hello")
data = await sftp.read("/tmp/hello.txt")
await sftp.close()

sftp, err := ssh.SFTP(ctx)
if err != nil {
    return err
}
defer sftp.Close(ctx)

if err := sftp.Write(ctx, "/tmp/hello.txt", []byte("hello")); err != nil {
    return err
}
data, err := sftp.Read(ctx, "/tmp/hello.txt")

</CodeGroup>

External clients

External client mode exposes a sandbox as an SSH server for tools that already speak SSH. This is the closest match for normal SSH usage: authorize a public key, serve the sandbox, then connect with ssh or sftp.

Authorize a key

bash

msb ssh authorize --file ~/.ssh/id_ed25519.pub
msb ssh authorize --key "ssh-ed25519 AAAA... user@host"
cat ~/.ssh/id_ed25519.pub | msb ssh authorize --stdin

Keys are appended to <MSB_HOME>/ssh/authorized_keys.

TCP listener

bash

msb ssh serve devbox

The default listener is 127.0.0.1:2222.

bash

ssh -p 2222 [email protected]
sftp -P 2222 [email protected]

Choose a different bind address or port when needed:

bash

msb ssh serve devbox --host 127.0.0.1 --port 2223

<Note> Binding to `0.0.0.0` exposes the SSH listener beyond the local machine. Keep the default loopback bind unless you intentionally want remote clients to connect. </Note>

ProxyCommand

msb ssh serve --stdio carries a single SSH connection over stdin/stdout instead of a TCP listener. Point OpenSSH at it with ProxyCommand so standard SSH tools can reach the sandbox by host alias.

Add an entry to your ~/.ssh/config:

sshconfig

Host devbox.msb
  User root
  ProxyCommand msb ssh serve devbox --stdio

The Host value is the alias you connect to, and devbox is the sandbox name passed to msb ssh serve.

Once it is in place, the alias works with any OpenSSH-based tool:

bash

ssh devbox.msb
sftp devbox.msb
scp ./build.tar devbox.msb:/tmp/
rsync -av ./src/ devbox.msb:/app/

Editors that build on OpenSSH, such as VS Code Remote-SSH, connect to the devbox.msb host the same way.

For exact SDK signatures, see the SSH reference for Rust, TypeScript, Python, or Go.