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rtail(1) - Terminal output to the browser in seconds, using UNIX pipes.

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# `rtail(1)`

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## Terminal output to the browser in seconds, using UNIX pipes.

`rtail` is a command line utility that grabs every line in `stdin` and broadcasts it over **UDP**. That's it. Nothing fancy. Nothing complicated. Tail log files, app output, or whatever you wish, using `rtail` broadcasting to an `rtail-server` – See multiple streams in the browser, in realtime.

## Running the server

The server ships as a container image — this is the recommended way to run it.

$ docker run -d --name rtail -p 8888:8888 -p 9999:9999/udp ghcr.io/kilianc/rtail

Open <http://localhost:8888> and start piping. There is a
[`docker-compose.yml`](docker-compose.yml) if you prefer:

$ docker compose up -d

Options are flags, or `RTAIL_*` environment variables:

$ docker run -d -p 8080:8080 -p 9999:9999/udp \
        -e RTAIL_WEB_PORT=8080 ghcr.io/kilianc/rtail

$ docker run -d -p 8888:8888 -p 9999:9999/udp \
        ghcr.io/kilianc/rtail --backlog 500

The image binds `0.0.0.0` inside the container, so **the published ports are
reachable from your whole network**. It has no authentication — keep it on a
trusted network, or put a reverse proxy in front of it.

## Installing the client

The client is a UNIX pipe and belongs on the host whose output you are tailing,
not in the container. It needs **Node.js 22.18 or newer** — rtail ships as
TypeScript and relies on Node stripping the types at load time, which is
unflagged from 22.18 on:

$ npm install -g rtail

`npm install -g rtail` also gives you `rtail-server`, if you would rather run
the server without Docker.

## Web app

![](https://s3.amazonaws.com/rtail/github/dark.png)

![](https://s3.amazonaws.com/rtail/github/light.png)

## Rationale

Whether you deploy your code on remote servers using multiple environments or simply have multiple projects, **you must `ssh` to each machine running your code, in order to monitor the logs in realtime**.

There are many log aggregation tools out there, but few of them are realtime. **Most other tools require you to change your application source code to support their logging protocol/transport**.

`rtail` is meant to be a replacement of [logio](https://github.com/NarrativeScience/Log.io/commits/master), which isn't actively maintained anymore, doesn't support node v0.12., and uses *TCP. (TCP requires strict client / server handshaking, is resource-hungry, and very difficult to scale.)*

**The `rtail` approach is very simple:**
* pipe something into `rtail` using [UNIX I/O redirection](http://www.westwind.com/reference/os-x/commandline/pipes.html) [[2]](http://www.codecoffee.com/tipsforlinux/articles2/042.html)
* broadcast every line using UDP
* `rtail-server`, **if listening**, will dispatch the stream into your browser, using [socket.io](http://socket.io/).

`rtail` is a realtime debugging and monitoring tool, which can display multiple aggregate streams via a modern web interface. **There is no persistent layer, nor does the tool store any data**. If you need a persistent layer, use something like [loggly](https://www.loggly.com/).

## Examples

In your app init script:

$ node server.js 2>&1 | rtail --id "api.myproject.com"

$ mycommand | rtail > server.log

$ node server.js 2>&1 | rtail --mute

Supports JSON5 lines:

$ while true; do echo [1, 2, 3, "hello"]; sleep 1; done | rtail
    $ echo { "foo": "bar" } | rtail
    $ echo { format: 'JSON5' } | rtail

Using log files (log rotate safe!):

$ node server.js 2>&1 > log.txt
    $ tail -F log.txt | rtail

For fun and debugging:

$ cat ~/myfile.txt | rtail
    $ echo "Server rebooted!" | rtail --id `hostname`

## Params

$ rtail --help
    Usage: cmd | rtail [OPTIONS]

Options:
      --host, -h     The server host                 [string] [default: "127.0.0.1"]
      --port, -p     The server port                        [string] [default: 9999]
      --id, --name   The log stream id                 [string] [default: (moniker)]
      --mute, -m     Don't pipe stdin with stdout                          [boolean]
      --tty          Keeps ansi colors                     [boolean] [default: true]
      --parse-date   Looks for dates to use as timestamp   [boolean] [default: true]
      --help         Show help                                             [boolean]
      --version, -v  Show version number                                   [boolean]

Examples:
      server | rtail > server.log         localhost + file
      server | rtail --id api.domain.com  Name the log stream
      server | rtail --host example.com   Sends to example.com
      server | rtail --port 43567         Uses custom port
      server | rtail --mute               No stdout
      server | rtail --no-tty             Strips ansi colors
      server | rtail --no-date-parse      Disable date parsing/stripping

## `rtail-server(1)`

`rtail-server` receives all messages broadcast from every `rtail` client, displaying all incoming log streams in a realtime web view. **Under the hood, the server uses [socket.io](http://socket.io) to pipe every incoming UDP message to the browser.**

There is little to no configuration – The default UDP/HTTP ports can be changed, but that's it.

## Examples

Use default values:

$ rtail-server

Always use latest, stable webapp:

$ rtail-server --web-version stable

Use custom ports:

$ rtail-server --web-port 8080 --udp-port 9090

Set debugging on:

$ DEBUG=rtail:* rtail-server

Open your browser and start tailing logs!

## Params

$ rtail-server --help
    Usage: rtail-server [OPTIONS]

Options:
    --udp-host, --uh  The listening UDP hostname            [default: "127.0.0.1"]
    --udp-port, --up  The listening UDP port                       [default: 9999]
    --web-host, --wh  The listening HTTP hostname           [default: "127.0.0.1"]
    --web-port, --wp  The listening HTTP port                      [default: 8888]
    --web-version     Define web app version to serve                     [string]
    --backlog, -b     Lines of history kept per stream    [number] [default: 100]
    --help, -h        Show help                                          [boolean]
    --version, -v     Show version number                                [boolean]

Every option can also be set as an environment variable, prefixed with
`RTAIL_` — `RTAIL_WEB_PORT=8080`, `RTAIL_BACKLOG=500`, and so on. This is how
the container image is configured.

Examples:
    rtail-server --web-port 8080         Use custom HTTP port
    rtail-server --udp-port 8080         Use custom UDP port
    rtail-server --web-version stable    Always uses latest stable webapp
    rtail-server --web-version unstable  Always uses latest unreleased webapp
    rtail-server --web-version 0.1.3     Use webapp v0.1.3

## The web view

### Filtering

The filter box takes a small query language rather than a bare regexp. Terms
are separated by spaces and **all** of them have to match; matching ignores
case until a term contains a capital, the way `ag` and `rg` behave.

| Query               | Matches                                          |
| ------------------- | ------------------------------------------------ |
| `payment failed`    | both words, in any order                         |
| `"payment failed"`  | that exact phrase                                |
| `-healthcheck`      | lines without it                                 |
| `/GET \/1\/users/`  | a regexp — add `/i`, `/s`, `/m` or `/u` for flags |
| `level:error`       | the JSON field contains `error`                  |
| `user.id=42`        | the JSON field is exactly `42`                   |
| `status!=200`       | it is anything else                              |
| `duration>250`      | `>`, `>=`, `<` and `<=`, on numbers              |
| `tags[0]:api`       | paths index into arrays                          |
| `trace_id:*`        | the field is there at all                        |

Field terms read the parsed payload, so `level:error` cannot be fooled by the
word "error" sitting in a message three keys away. A field term never matches a
line that does not carry the field — including `status!=200`, which means "has
a status, and it is not 200". For "not 200, whether or not there is a status",
negate the whole term instead: `-status:200`.

Matches are marked in the viewport, and the box counts how many lines survived.
An unfinished regexp turns the box's hairline red and keeps filtering on the
terms that did parse. Press `f` to jump to the box, `Escape` to clear it.

### Extracting fields

`Fields` picks JSON paths out of object lines: `event=checkout.completed
count=305 ok=false` instead of the whole payload. The list is a census of the
paths in the buffer, most common first, and takes a hand-typed path for
anything that has not come past yet. The picks belong to the stream — the
fields of a billing worker are not the fields of an nginx log — and are
remembered per stream.

### JSON payloads

Not every payload is worth six rows of the viewport. **Settings → JSON
payloads** decides what an object line looks like before you touch it:

* **Auto** (default) — expanded up to six rows, collapsed past that.
* **One line** — always collapsed, truncated at the edge of the window.
* **Pretty** — always expanded.

The caret at the start of any object line overrides that for that line, whether
it is showing a payload or extracted fields.

## UDP Broadcasting

To scale and broadcast on multiple servers, instruct the `rtail` client to stream to the broadcast address. Every message will then be delivered to all servers in your subnet.

## Authentication layer

For the time being, the webapp doesn't have an authentication layer; it assumes that you will run it behind a VPN or reverse proxy, with a simple `Authorization` header check.

# Running it locally

Note there are two images, and they are not the same thing:
[`Dockerfile`](Dockerfile) is the server you deploy, and
[`tools/Dockerfile`](tools/Dockerfile) below is the development toolchain,
which mounts your checkout.

The toolchain lives in a container ([`tools/Dockerfile`](tools/Dockerfile)), so Docker is
the only thing you need installed — no Node.js, no npm, no global CLIs.

$ make dev

That builds the assets, starts `rtail-server`, feeds it three live demo
streams, and serves the webapp. It prints the URL — `make url` prints it
again. Stylesheets recompile on save; reload the browser to pick them up.
`Ctrl-C` stops everything.

The first run also builds the toolchain image and installs dependencies, so it
takes a minute; subsequent runs start immediately.

To leave it running in the background instead:

$ make up         # start detached, wait for it, print the URL
    $ make logs       # tail it
    $ make down       # stop it

Other targets:

$ make build      # build the webapp into app/
    $ make dist       # build the minified webapp into dist/
    $ make test       # unit + integration suite, with coverage thresholds
    $ make test-e2e   # browser smoke suite (first run downloads Chromium)
    $ make typecheck  # type-check everything
    $ make shell      # open a shell inside the toolchain container
    $ make clean      # remove generated assets and dependencies

### Ports

Ports are derived from the worktree path, so several checkouts of this repo can
run at once without colliding. Each gets its own HTTP port, UDP port, and
container name, fixed across runs — sharing any of the three fails confusingly,
since two servers can both bind the same UDP port and the loser simply never
receives a log line.

`make url` reports the current one. Override with `make dev PORT=9000
UDP_PORT=9001`.

If you do have a Node.js toolchain on your machine, the same targets are plain
npm scripts — `npm install && npm run dev`.

### The stack

| | |
| --- | --- |
| CLI | TypeScript, ESM, Node ≥ 22.18, [yargs](https://yargs.js.org), [socket.io](https://socket.io) |
| Webapp | [Preact](https://preactjs.com) + TypeScript, ~33 KB gzipped |
| Build | [esbuild](https://esbuild.github.io) + [dart-sass](https://sass-lang.com) |
| Tests | the built-in `node:test` runner, [jsdom](https://github.com/jsdom/jsdom), [Playwright](https://playwright.dev) |

The webapp has no framework runtime beyond Preact: routing, preferences,
popovers, and timestamp formatting are a few dozen lines each over the
platform (`history`, `localStorage`, `Intl`) rather than dependencies.

The CLI has no build step at all. `bin` points straight at the `.ts` sources
and Node strips the types as it loads them, so what you read in `cli/` is
exactly what npm installs — nothing is compiled, bundled, or minified on the
way. `tsc` never emits; it only type-checks, and `erasableSyntaxOnly` keeps the
source to constructs that *can* be erased (no enums, namespaces, or constructor
parameter properties, all of which would need real codegen).

# How to contribute

`main` is the only long-lived branch, and it is always releasable.

* Branch off `main`, and open a pull request back into `main`
* Keep the branch short-lived; there is no `develop` or release branch to merge through
* CI must be green before a pull request lands

There are three layers, and a change usually wants a test in exactly one of
them:

| Layer | Where | What it covers |
| --- | --- | --- |
| Unit | `test/unit` | The CLI modules, the webapp's libraries, and each Preact component against [jsdom](https://github.com/jsdom/jsdom) |
| Integration | `test/integration` | The real `bin` entry points, spawned as processes and talking over a real UDP socket |
| End to end | `test/e2e` | The published build in a real browser, fed by the real client bin |

The first two run on the built-in [`node:test`](https://nodejs.org/api/test.html)
runner and are what you want almost always. They are fast (a few seconds) and
enforce a **90% line, branch and function coverage floor** — the run fails if a
change drops below it.

$ make test

The browser suite is slower and needs its own image, so it is a separate target
and a separate CI job:

$ make test-e2e

Everything is TypeScript; please keep it type-clean:

$ make typecheck

One wrinkle worth knowing: Node cannot load `.tsx` at all — type stripping is
an erasure pass and JSX needs a real transform — so `tools/tsx-hook.ts` runs
the components through esbuild on the way into the test runner, using the same
JSX settings as `tools/build.ts`. Source maps are inline, so coverage still
reports against the original `.tsx` lines.

CI runs the unit and integration suites plus the production build on Node 22.18
and 24, and the browser suite on 22.18.

## Releasing

The `version` field in `package.json` is the release trigger. Bump it in a pull
request like any other change; when that pull request lands on `main`, CI
re-runs the type-check, build, and tests, then tags the commit `vX.Y.Z`, cuts a
GitHub release with generated notes, and pushes the multi-arch container image
to `ghcr.io/kilianc/rtail`.

A version with a pre-release suffix (`0.3.0-rc.1`) is marked as a pre-release
and is never tagged `latest`. Landing anything else on `main` releases nothing.

## Contributors

* [Kilian Ciuffolo](https://github.com/kilianc)
* [Luca Orio](https://www.behance.net/lucaorio)
* [Sandaruwan Silva](https://github.com/s-silva)
* [Sorel Mihai](https://dribbble.com/sorelmihai)
* [Tim Riot](https://www.linkedin.com/in/timriot)

## Roadmap (aka where you can help)

* Optional HTTP basic auth on the web port, and a shared secret on UDP ingest.
  Full OAuth ([#44](https://github.com/kilianc/rtail/issues/44)) needs a user
  model and session storage, which is a lot of machinery for a tool with no
  persistence layer — basic auth covers the actual risk.
* A catch-all docker logs image: watch `docker events`, pipe every container's
  `docker logs -f` into a stream named after it.
* Broaden the test suite, particularly around the UDP ingest path.

Dropped, and why:

* ~~Rewrite webapp using ng2~~ — done differently. The webapp is now Preact +
  TypeScript; Angular 2 was already obsolete by the time it came up.
* ~~Publish base rtail docker image to DockerHub~~ — done, but to GHCR rather
  than DockerHub, since it needs no separate account or secrets.
* ~~Write a rock solid test suite~~ — a suite exists and runs in CI. Deepening
  it is the open item above.
* ~~Allow use of DTLS~~ — the linked PR was against `joyent/node`, a repo that
  no longer exists, and Node core still has no DTLS. Run rtail over WireGuard
  or Tailscale instead; that is the modern answer to this problem.
* ~~Infinite-scroll in the webapp~~ — cannot be built as stated. The server
  keeps a fixed-size ring buffer per stream and sends it in one message; there
  is no pagination to scroll through. Real history means a persistence layer,
  which contradicts the design. `--backlog` covers the useful part.

## Sponsors
❤ rTail? Consider sponsoring this project to keep it alive and free for the community.

* ? (wildcard TLS cert)
* ? (.io domain)

[![PayPal donate button](https://img.shields.io/badge/$_paypal-one_time_donation_➝-04cd7e.svg?style=flat-square)](https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=info%40rtail%2eorg&lc=US&item_name=rtail&item_number=rtail&currency_code=USD&bn=PP%2dDonationsBF%3abtn_donateCC_LG%2egif%3aNonHosted)

## License

_This software is released under the MIT license cited below_.

Permission is hereby granted, free of charge, to any person
    obtaining a copy of this software and associated documentation
    files (the 'Software'), to deal in the Software without
    restriction, including without limitation the rights to use,
    copy, modify, merge, publish, distribute, sublicense, and/or sell
    copies of the Software, and to permit persons to whom the
    Software is furnished to do so, subject to the following
    conditions:

The above copyright notice and this permission notice shall be
    included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND,
    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
    OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
    NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
    HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
    WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
    OTHER DEALINGS IN THE SOFTWARE.

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