MPC Sample — temporary root SSH over USB

By puckcv on MPC-Forums. Target: Akai MPC Sample AC50/AZ07, firmware 1.3.0.12.

Starts the built-in OpenSSH server through the stock SD autorun mechanism. No firmware flashing or modified Akai binary is required. The device-side autorun in this repository is the exact version the author successfully used to log in on 19 October 2026. Version 1.2 starts SSH in a separate temporary service: waiting for USB happens outside autorun, with all runtime logs in RAM. SSH starts automatically when the prepared SD is detected; there is no dialog.

Hardware validation: two full cold boots with the prepared SD inserted, successful root SSH on both boots, and normal interface/sound confirmed by the device owner. The stock application hash and launch configuration remained unchanged. This is validation on one MPC Sample, not on every firmware/device.

USB address: 192.168.155.1 · SSH port: 2222 · User: root

This is the MPC-side USB address used by this setup; it is not your Wi-Fi/router address. Do not replace it with the computer's address. Other firmware versions and beta builds have not been verified. macOS/Linux setup is host-tested; the Windows setup script is provided but has not been run on Windows by the author.

Version 1.2 starts USB-only root SSH automatically with your personal keys. You can leave the prepared SD inserted during startup or insert it after boot. To start without SSH, boot without the autorun card. Removing SD later does not stop a server that has already started.

1. Download

Download mpc-sample-root-ssh-v1.2.0.zip from Releases and extract it on your computer. Use this fresh public download for each new person/device. Do not download or reuse somebody else's prepared SD folder.

You need an exFAT SD card, an SD reader, a USB-C data cable and an SSH client. Save your MPC project before testing. Back up an existing autorun folder on the SD card; do not merge two autorun packages or reformat a card containing data.

2. Generate your own keys on the computer

Choose one setup method below. Both create:

File	Where it belongs
mpc_sample_client_ed25519	Private client key: stays in your computer's .ssh folder
mpc_sample_client_ed25519.pub	Client public key: copied to autorun/authorized_keys
ssh_host_ed25519_key	Separate private server identity: on your personal SD, then copied to MPC RAM
ssh_host_ed25519_key.pub	Public server identity: used to check the first-connection fingerprint

macOS / Linux

Open Terminal in the extracted mpc-sample-root-ssh folder. If you extracted it to Downloads, this is normally:

cd ~/Downloads/mpc-sample-root-ssh
sh setup_unix.sh

The script first checks autorun.check, then creates the keys. Choose a passphrase when asked for the client key and enter it again to confirm. Nothing appears while you type the passphrase; that is normal. The separate host key is generated automatically without a passphrase so the MPC can start the server. No keys are downloaded from anyone else.

Wait for PERSONAL_AUTORUN_PREPARED. Keep the displayed host fingerprint for the first connection. You can display it again from this folder:

ssh-keygen -lf autorun/ssh_host_ed25519_key.pub

If the client-key filename already exists, setup stops instead of overwriting it. Use a fresh extraction and choose a new filename, for example:

MPC_CLIENT_KEY="$HOME/.ssh/mpc_sample_client_new_ed25519" sh setup_unix.sh

Then use that new path in the SSH command. Do not run setup with sudo.

Windows

Open PowerShell in the extracted folder. Check that OpenSSH Client is available:

Get-Command ssh, ssh-keygen

If either command is missing, install the OpenSSH Client Windows optional feature first. Run the included local setup script:

powershell -NoProfile -ExecutionPolicy Bypass -File .\setup_windows.ps1

This execution-policy option applies to that PowerShell process only. Inspect the local script before running it. For the client key, choose and confirm a passphrase. When the script announces the separate SERVER HOST key, leave its passphrase empty: press Enter twice. Wait for PERSONAL_AUTORUN_PREPARED and keep the displayed host fingerprint.

If a client key already exists, use a fresh extraction and a new filename:

$env:MPC_CLIENT_KEY = "$HOME\.ssh\mpc_sample_client_new_ed25519"
powershell -NoProfile -ExecutionPolicy Bypass -File .\setup_windows.ps1

Use the selected filename when connecting. Setup never intentionally overwrites keys.

3. Prepare the SD card

Copy the whole generated autorun folder to the root of the exFAT SD. The result must be:

SD card/
└── autorun/
    ├── autorun.json
    ├── autorun.check
    ├── autorun.sh
    ├── authorized_keys
    ├── ssh_host_ed25519_key
    └── ssh_host_ed25519_key.pub

Do not put the entire extracted repository inside autorun, and do not copy only the contents of autorun directly into the SD root. Keep the client private key on the computer. Safely eject the SD card from the computer.

4. Start SSH on the MPC

1. Save your project and safely eject the prepared SD from the computer.
2. Connect the MPC to the computer using a USB-C data cable.
3. Either insert the SD into the MPC's own slot before powering on, or insert/ mount it through the normal storage interface after the MPC has booted.
4. SSH starts automatically. There is no Start SSH prompt in version 1.2.
5. Allow normal MPC startup and up to 45 seconds for USB networking.

No USB mass-storage/controller-mode switch or Wi-Fi connection is required. USB mass-storage mode exposes the SD to the computer; it is a different use from running the MPC normally with USB networking for SSH.

If USB was absent for the entire 45-second wait, connect the cable and safely unmount/reinsert/mount the SD, or normally reboot with the card and cable attached. The SSH worker times out independently; it does not make autorun wait for USB.

5. Connect from the computer

macOS / Linux Terminal:

ssh -p 2222 -i ~/.ssh/mpc_sample_client_ed25519 root@192.168.155.1

Windows PowerShell:

ssh -p 2222 -i "$HOME\.ssh\mpc_sample_client_ed25519" root@192.168.155.1

On the first connection, compare the server fingerprint with the one printed by setup. If it matches, type yes. When asked for the key passphrase, enter the client-key passphrase you chose on your computer. There is no shared root password. If you chose another key filename, adjust the -i argument.

After login, run:

id

Expected: uid=0(root). You now have a root shell. Use exit to disconnect. Disconnecting the client does not stop the server.

6. Troubleshooting

• No Start SSH prompt: expected in version 1.2. Connect using the command above; this version starts SSH automatically when the prepared card is detected.

• Connection refused: wait up to 45 seconds. Check that this SD was prepared with your keys, the folder layout is correct, and the MPC is in normal operation rather than USB mass-storage mode. If USB was connected too late, safely unmount/reinsert/mount the card or normally reboot with USB attached.

• USB/network startup errors: after obtaining SSH, inspect the RAM logs:

  systemctl status mpc-sample-usb-ssh.service --no-pager
  cat /run/mpc-sample-ssh/setup.log
  cat /run/mpc-sample-ssh/worker.log

  Version 1.2 does not create new SSH_START.txt / SSH_AUTH_LOG.txt on SD. Old SD reports can remain from an earlier version; their timestamps do not describe the current run.

• MPC hangs during project loading: if the device is stuck, press and hold power until it switches off, remove the SD, then boot without it. Restore the working backup if needed. A forced shutdown can lose unsaved work. Earlier versions could hang when booted with the autorun card inserted; v1.2 moves startup work to a separate service and removes the startup dialog.

• Connection timed out / no route: check the USB connection and the computer's USB network interface. The target is 192.168.155.1, not the computer's IP.

• Permission denied (publickey): use the private client key belonging to the public key copied into this card's authorized_keys.

• Key already exists: do not delete an existing key; choose a new filename with MPC_CLIENT_KEY as described above.

• Host identification changed: check that you intentionally generated a new server host key and compare fingerprints. If confirmed, remove only this endpoint's old known-host entry, then reconnect:

  ssh-keygen -R "[192.168.155.1]:2222"

Review logs before sharing them; they may contain authentication details.

7. Stop and remove

Save your work, disconnect SSH with exit, then use a normal MPC shutdown/ reboot. The temporary server/configuration do not survive reboot. To boot without SSH, leave the autorun card out. Removing the card alone does not stop an already running SSH server. Back up/remove the personal autorun folder from the card on your computer when you no longer need it.

Sharing and scope

Share the public repository/release ZIP only. Never publish a prepared SD folder, private keys or personal SSH logs. Every person generates their own client key and a separate host key for their device.

The script configures the existing sshd for root public-key login only, bound to the USB address. Password login and forwarding are disabled. Configuration, active credentials, logs and the temporary service are all under /run. It does not flash firmware, replace the stock app, restart ac50.service, or modify persistent SSH configuration. Normal OS activity may independently write to internal storage. A root shell can modify the device: this kit supplies access, not a recovery guarantee or a patched firmware.

For contributors, python3 tools/check_autorun.py verifies the exact-byte checksum and python3 tools/build_release.py creates a keyless ZIP using a fixed allowlist. The checksum covers raw JSON + script + firmware-specific salt; generated keys are not listed in files[], so key generation does not change it. Any edit to the manifest or autorun script requires a new checksum and testing.