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README.md

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+# Custom Alpine Image
+
+This repository contains the necessary files to build a customizable Alpine Linux Docker image. The image can be configured at runtime by providing a `sysconfig.toml` file.
+
+## How to build the image
+
+To build the Docker image, run the following command from the root of this repository:
+
+```sh
+docker build -t alpine-customizable .
+```
+
+## How to configure the image
+
+You can configure the container at runtime by mounting a `sysconfig.toml` file at `/etc/sysconfig.toml`.
+
+```sh
+docker run -it --rm -v ./sysconfig.toml:/etc/sysconfig.toml alpine-customizable
+```
+
+The `sysconfig.toml` file supports the following sections for configuration:
+
+### `[general]`
+
+This section is used for general system-wide settings.
+
+-   `packages`: A list of strings specifying additional Alpine packages to install using `apk add`.
+
+    *Example:*
+    ```toml
+    [general]
+    packages = ["openssh-server", "curl"]
+    ```
+
+### `[users]`
+
+This section allows you to define users that will be created on the container. Each user is defined in a sub-section using the format `[users.username]`.
+
+The following keys are supported for each user:
+
+-   `password` (optional): A string to set the user's password.
+-   `pubkeys` (optional): A list of public SSH keys (strings) to add to the user's `~/.ssh/authorized_keys` file, enabling key-based authentication.
+
+    *Example:*
+    ```toml
+    [users.dmitry]
+    password = "a-secure-password"
+    pubkeys = [
+        "ssh-rsa AAAA...",
+        "ssh-ed25519 AAAA..."
+    ]
+    ```
+
+### `[groups]`
+
+This section allows you to define groups and manage their members. Each group is defined in a sub-section using the format `[groups.groupname]`.
+
+The following keys are supported for each group:
+
+-   `users`: A list of usernames to be added to this group. These users should typically be defined in the `[users]` section or already exist on the system.
+
+    *Example:*
+    ```toml
+    [groups.sftp-users]
+    users = ["dmitry"]
+    ```
+
+### `[configs]`
+
+This section allows you to create arbitrary configuration files on the container's filesystem. Each file is defined in a sub-section where the name is the full, quoted path to the file, e.g., `[configs."/etc/motd"]`.
+
+The following keys are supported for each file:
+
+-   `body` (required): A string (often a multi-line string) containing the content of the file.
+-   `permissions` (optional): An integer representing the file permissions in standard Linux octal notation (e.g., `644`, `755`).
+-   `owner` (optional): A string in `"user:group"` format to set the file's ownership.
+
+    *Example:*
+    ```toml
+    [configs."/etc/ssh/sshd_config.d/sftp.conf"]
+    body = """
+    Match group sftp-users
+      ChrootDirectory /chroot
+      ForceCommand internal-sftp
+      AllowTcpForwarding no
+    """
+    permissions = 644
+    owner = "root:root"
+    ```