shell-tunnel

Ultra-lightweight remote shell gateway.

A single binary that exposes command execution on a machine as a structured REST/WebSocket API — typed JSON requests and responses, resource-style sessions — so scripts, tools, and services can drive that machine programmatically.

Not a browser terminal or screen-sharing UI (cf. ttyd, gotty, wetty, sshx), not a remote-desktop product, not a general-purpose tunneling / reverse-proxy product, not a multi-user collaboration surface. The consumer is a program calling an API, not a person at a terminal.

Try it in 30 seconds

cargo install shell-tunnel      # or grab a release binary, below

shell-tunnel                    # listens on 127.0.0.1:3000, no auth, local only

From another terminal:

curl -X POST http://127.0.0.1:3000/api/v1/execute \
  -H "Content-Type: application/json" \
  -d '{"command":"echo hello"}'
# {"success":true,"exit_code":0,"output":"hello\n","duration_ms":5,"timed_out":false,
#  "total_bytes":6,"truncated":false}

That's the whole loop: run the binary, POST a command, get structured output. No config, no account, no daemon. When you want auth or a public URL, add one flag at a time — the next section shows each, including TLS on a relay you host. The gateway's own socket is plaintext.

Install

cargo install shell-tunnel

# or a release binary (linux x64/arm64, macOS x64/arm64, windows x64)
curl -LO https://github.com/iyulab/shell-tunnel/releases/latest/download/shell-tunnel-linux-x64.tar.gz
tar xzf shell-tunnel-linux-x64.tar.gz && sudo mv shell-tunnel /usr/local/bin/

Release binaries can update themselves: shell-tunnel --update.

How it works

There is no separate server to install: the binary is the server. You run it on the machine you want to control, it listens on an HTTP port, and clients drive that machine by calling the API.

client ──HTTP/WS──▶ shell-tunnel (on the target machine) ──▶ shell

Behind NAT that port is not reachable on its own, so shell-tunnel can publish it for you — either through a tunnel client (--tunnel) or through a relay you run yourself (--relay). Only the server side ever needs inbound connectivity; a caller behind NAT is fine, because it only makes outbound requests.

Reaching a machine behind NAT

The intended shape: a target you cannot reach directly, a relay with a public address, and you calling in from wherever.

target (NAT) ──dials out──▶ relay (public) ◀──you call── caller (NAT)

On the relay host — the only machine that needs an inbound port:

shell-tunnel relay -H 0.0.0.0 -p 8443 --tls-self-signed --public-base https://relay.example.com

--public-base names the host; the advertised URL uses this relay's port (8443). It generates a certificate and an enrolment token on first run and prints the exact command a device needs — including the certificate fingerprint, so nothing has to be copied:

Devices join with:
    shell-tunnel --relay https://relay.example.com:8443 --enroll-token st_… --relay-fingerprint sha256:…

On the target — no port forwarding, it dials out:

shell-tunnel --relay https://relay.example.com:8443 --enroll-token st_… \
             --relay-fingerprint sha256:… -k my-api-key --preset operator

From anywhere — the target is now reachable at /d/<name>:

curl -X POST https://relay.example.com:8443/d/<name>/api/v1/execute \
  -H "Authorization: Bearer my-api-key" \
  -H "Content-Type: application/json" \
  -d '{"command":"hostname"}'

To list what is attached without logging into any target: curl -H "Authorization: Bearer <enroll-token>" https://relay.example.com:8443/relay/v1/devices.

No public relay of your own? shell-tunnel --tunnel --preset operator runs cloudflared and prints a trycloudflare.com URL instead — quick to try, but Cloudflare documents it as testing-only. See docs/USAGE.md for both paths in full.

Moving files

The file API reaches what the account running the server reaches — the same places a command it runs would. No flag needed:

shell-tunnel --require-auth --preset operator

Downloads are ordinary HTTP with Range, so an interrupted transfer resumes with the same header any HTTP client already speaks. Uploads run as a session: declare the size and SHA-256, send chunks, and the file appears at its destination only once the whole thing verifies. That is the point of these endpoints: a large transfer that resumes and verifies, rather than bytes piped through a command.

Resuming an upload is worth reading before you need it. A timeout on a chunk means the outcome is unknown, not that the chunk was lost — the server may well have written it — so asking the session where it is beats assuming the worst and starting over. USAGE §3.2 gives the two ways to ask, and the chunk size to use comes from the server rather than from a constant in your client: it is smaller when the device is reached through a relay.

Directory removal is opt-in (recursive=true) and can be previewed (dry_run=true) — a guard against a caller's mistake, not against a caller, since a token that can already remove one file this way can remove anything the server can reach.

To confine them to one directory instead, name it:

shell-tunnel --fs-root /srv/deploy --require-auth --preset file-write

That confinement is worth something for a token holding fs.read/fs.write and not exec — a deploy push, say. --preset file-write (fs.read, fs.write) and --preset file-read (fs.read) are exactly those tokens, and they are the only presets --fs-root genuinely confines: it is not a boundary against a token that can run commands, since such a token can already read and write anything the server can. Pair a file-* preset with --fs-root — without it the token reaches the whole machine, and the startup banner says so.

A word on exposure

Publishing a shell means anyone holding the token can run commands as the user running shell-tunnel. So a public path (--tunnel or --relay), or simply binding to a non-loopback address, turns authentication on, generates a key if you gave none, refuses --no-auth, scopes the issued token to operator instead of the wildcard, and appends an audit trail to shell-tunnel-audit.jsonl in the working directory (--audit-log puts it elsewhere). Naming a scope yourself still wins — --preset full-control keeps the wildcard. Note what operator is and is not: it holds every capability this version defines, so it withholds nothing today and the difference from the wildcard is only that it will not automatically carry capabilities added later. The narrowing presets are file-read and file-write. Keep rate limiting on, and treat the URL and token as credentials. TLS is not optional over the internet — --tls-self-signed on the relay is one flag, and the fingerprint it prints keeps the connection authenticated, not just encrypted. The startup banner states what is actually in force.

Documentation

Status

Implemented: sessions, one-shot and streaming execution, WebSocket, capability-scoped auth, rate limiting, public exposure (Cloudflare tunnel or self-hosted relay), in-process TLS on the relay with self-signed generation and fingerprint pinning, host-header checking, an append-only audit trail, and filesystem operations (list, read, write, delete, optionally confined by --fs-root). On the roadmap: native MCP tools.

License

MIT — see LICENSE.