CrossShell

Two machines, one desk. CrossShell links a Linux daily driver and a Windows build box (or any mix of Linux and Windows machines) on the same network:

• SSH both ways, set up for you. CrossShell enables the OS's own OpenSSH server, pairs the machines with a 6-digit code, swaps keys and pins host keys. Afterwards ssh <name> works from any terminal — and so do VS Code Remote-SSH, rsync, scp and git.
• Terminal, files and port forwards in the app, over that SSH.
• Remote desktop, TeamViewer-style: view or control the other screen. It's CrossShell's own engine, tunneled through SSH, so it works on Windows Home (which has no RDP server) and on Wayland, opens no extra ports, and needs no third-party server.

How it works

 Linux  ───────────── LAN ─────────────  Windows
 CrossShell app                           CrossShell app
   │  pairing (TCP 47820, once)  ◄────►     │
   │  discovery (UDP 47820)      ◄────►     │
   │                                        │
   ├─ ssh / sftp ─────────────────────────► sshd (OpenSSH Server)
   └─ ssh -L ── remote desktop ──────────►  └─ crossshell-host (127.0.0.1 only)
 sshd ◄────────────────────────────────── ssh / sftp / ssh -L

• Pairing uses an ephemeral X25519 exchange with a commitment and shows the same 6-digit code on both screens. If the codes match, each side sends its SSH user, its client key and its sshd host keys, sealed with a key only the two of them have. Nobody types passwords and nothing is trusted on first use.
• Trust lives in standard files in ~/.ssh/crossshell/ (config, known_hosts, id_ed25519), plus one Include line at the top of ~/.ssh/config. Peer keys go into authorized_keys, or on Windows admin accounts into C:\ProgramData\ssh\administrators_authorized_keys. Each line carries a crossshell:<peer-id> marker so unpairing removes exactly that line.
• Remote desktop: the host agent listens on 127.0.0.1 only and writes a fresh random token to a file only its user can read. The viewer reads that file over SSH, opens an SSH tunnel and authenticates with the token. SSH is the only way in.

See PLAN.md for the full design, wire protocol and pairing spec.

Install

Download from the releases page:

• Linux (x64): crossshell-<ver>-linux-x64.tar.gz. Extract it and run ./cross_shell. You need the OpenSSH client (ssh, ssh-keygen) and GTK 3. Screen sharing uses PipeWire, which any current desktop has.
• Windows 10/11 (x64): crossshell-<ver>-windows-x64.zip. Extract it and run cross_shell.exe. The OpenSSH client ships with Windows; the app can install OpenSSH Server for you.

The builds are not code-signed yet. On Windows, SmartScreen will warn on first launch. If Smart App Control is on, it may block cross_shell.exe or the screen-share agent crossshell-host.exe. The app tells you when that happens. Signed releases are planned.

Verify downloads with SHA256SUMS.

Use it

1. Install and open CrossShell on both machines.
2. Open This machine (the gear icon) and fix anything red. Usually that means Set up SSH server, which takes one admin prompt (UAC on Windows, polkit on Linux).
3. The other machine appears under Nearby. Click Pair and check that both screens show the same code.
4. Use the machine card: Terminal, Files, Remote desktop, or More for view-only, port forwards, system terminal, VS Code and unpairing.

From any terminal afterwards:

ssh winbox

Limits (honest list)

• Windows secure desktop: UAC prompts, the lock screen and the sign-in screen can't be captured by an agent running in your session. The viewer shows a notice until they go away.
• Windows elevated windows: these can be driven when the agent runs with highest privileges. That is automatic for admin users when the session is started remotely.
• Linux on GNOME: sharing uses Mutter's remote-desktop API, with no prompt. On other Wayland desktops the xdg portal shows a consent dialog once, and a restore token avoids it afterwards. On X11 it uses XShm + XTest.
• Terminal input: the built-in terminal takes keys directly from the keyboard, so input methods (IME) and dead-key compose sequences don't reach it. Use Open in system terminal for those.
• LAN only: across the internet, put both machines on a VPN (Tailscale, WireGuard) and use Pair by address.

Build

scripts/build-linux.sh                     # dist/crossshell-<ver>-linux-x64.tar.gz
scripts/build-windows.sh user@winbox       # dist/crossshell-<ver>-windows-x64.zip

Layout: app/ is the Flutter UI (Linux + Windows) and engine/ is the Rust workspace:

• crossshell-proto: wire protocol and tile codec
• crossshell-host: agent
• crossshell-view: viewer
• platform-*: capture/input backends

Tests:

cd engine && cargo test --release
cd app && flutter test

License

MIT