# Startup, eggs and variables

> The startup command, the container image and the egg's variables — three fields that change what the server actually is.

Source: https://stygion.eu/docs/panel/startup
Updated: 2026-08-30

![The Startup tab](https://stygion.eu/shots/panel/startup.webp)

The **Startup** tab is how the server is launched. Three things, and
each can break a server as easily as fix it.

## The startup command

One line, run under `bash` inside the container. For Minecraft,
typically:

```
java -Xms{{SERVER_MEMORY}}M -Xmx{{SERVER_MEMORY}}M -jar {{SERVER_JARFILE}} nogui
```

Variables are referenced with **double curly braces**. An unknown
variable renders empty — so `-XmxM` means the name is misspelled, not
that something deeper is broken.

The panel supplies three variables always, even when the egg does not
declare them:

| Variable | What is in it |
|---|---|
| `SERVER_MEMORY` | The memory limit in MB (1024 when unlimited) |
| `SERVER_IP` | `0.0.0.0` |
| `SERVER_PORT` | The primary [allocation](/docs/panel/sit) |

Bash works in full here — `[[ ]]`, `$( )`, backticks. Startup commands
from Pterodactyl eggs therefore work unchanged.

## The image

The **Docker image** is the environment the server runs in: which Java,
which libraries. An egg usually offers several (Java 8, 17, 21), and any
reference can be typed in.

Changing the image changes the runtime, not the data. A modpack built
for Java 17 will not boot under Java 8, and says so immediately in the
[console](/docs/panel/konzole).

## Variables

Whatever the egg exposes — jar name, version, an API key, switches. The
panel shows the egg's own labels beside them, so no field has to be
guessed at.

## Saving rebuilds the container

Saving Startup **rebuilds the container**. It has to: the command, the
image and the variables are part of the container, not something that
can be changed while it runs.

The data directory is not touched. The panel also takes the opportunity
to restore the pipe the console sends commands down, which makes saving
Startup the quickest way to move a server onto today's console.

## Reinstalling

**Settings → Reinstall server** runs the egg's install script again. It
is for an install that failed the first time, or a change of game
version. Egg scripts usually overwrite the server's files and **leave
the world alone** — but that is the egg's script, not a guarantee from
the panel. Take a [backup](/docs/panel/zalohy) first.

Next: [Server settings](/docs/panel/nastaveni).