# Didactyl Server Installation Guide — systemd + Dedicated User Model

## Overview

This document describes how to install Didactyl on a Linux server as a dedicated system user, managed by systemd, with scoped sudo privileges for server maintenance tasks.

The mental model: **Didactyl is a person on your server.** It gets its own home directory, its own login identity, and explicit permission to manage the services you delegate to it — nothing more.

## Architecture

```mermaid
graph TD
    subgraph Internet
        RELAYS[Nostr Relays<br/>wss://relay.damus.io<br/>wss://relay.primal.net]
        LLM_API[LLM Provider API<br/>OpenAI / PPQ / Ollama]
    end

    subgraph Server
        subgraph "systemd"
            SVC[didactyl.service<br/>User=didactyl<br/>Group=didactyl]
        end

        subgraph "/home/didactyl/"
            BIN[didactyl binary]
            CFG[genesis.jsonc<br/>mode 600]
            LOGS[context.log.md<br/>didactyl.log]
        end

        subgraph "Privilege Boundary"
            SUDOERS[/etc/sudoers.d/didactyl<br/>Whitelisted commands only]
        end

        subgraph "Unprivileged Commands"
            MON[free / df / uptime<br/>ps / cat /proc/*<br/>ss -tlnp / top]
        end

        subgraph "Privileged Commands via sudo"
            SYSD[systemctl status/restart/start/stop<br/>journalctl<br/>daemon-reload]
        end
    end

    ADMIN[Administrator<br/>via Nostr DM] -->|NIP-04 encrypted| RELAYS
    RELAYS <-->|WebSocket| SVC
    SVC --> BIN
    BIN <-->|HTTPS| LLM_API
    BIN -->|popen as didactyl| MON
    BIN -->|sudo via popen| SUDOERS
    SUDOERS --> SYSD

    style CFG fill:#f66,stroke:#333,color:#fff
    style SUDOERS fill:#ff9,stroke:#333
    style SVC fill:#9f9,stroke:#333
```

## Security Model

### Privilege Tiers

Didactyl enforces three privilege tiers for inbound Nostr messages (see `src/config.h` security_config_t):

| Tier | Who | Can use tools? | Can chat? |
|------|-----|---------------|-----------|
| **ADMIN** | Your npub (config `admin.pubkey`) | ✅ Yes | ✅ Yes |
| **WoT** | Contacts in your follow list | ❌ No (configurable) | ✅ Yes |
| **Stranger** | Everyone else | ❌ No | Canned response or ignored |

Only the ADMIN tier can trigger `local_shell_exec` — the tool that runs commands on the server.

### OS-Level Privilege Separation

The `local_shell_exec` tool in `src/tools/tool_local.c` calls `popen()` directly. Whatever the process user can do, the agent can do. This is why we:

1. Run as a **dedicated unprivileged user** (`didactyl`)
2. Grant **specific sudo permissions** via `/etc/sudoers.d/didactyl`
3. Use **systemd sandboxing** directives to limit filesystem access

### What the Agent Cannot Do

With the configuration described in this guide:

- ❌ Write anywhere outside `/home/didactyl/`
- ❌ Run arbitrary root commands not in the sudoers whitelist
- ❌ Install or remove packages (unless explicitly whitelisted)
- ❌ Modify system configuration files in `/etc/`
- ❌ Access other users' home directories (with proper home directory permissions)
- ❌ Accept tool commands from anyone except the ADMIN pubkey

---

## Installation Steps

### Prerequisites

- A Linux server with systemd (Debian/Ubuntu, RHEL/Fedora, Arch, etc.)
- Network access to Nostr relays and your LLM provider
- The Didactyl static binary (download from releases or build with `./build_static.sh`)
- A Nostr keypair for the agent (nsec)
- Your admin Nostr keypair (npub)
- An LLM API key

### Step 1: Create the Didactyl User

```bash
# Create a regular user with a home directory and bash shell
sudo useradd -m -s /bin/bash -c "Didactyl Nostr Agent" didactyl
```

**Why bash and not nologin?** The `local_shell_exec` tool runs commands via `sh -lc` (login shell). A real shell ensures PATH, locale, and environment are properly initialized. The agent needs to "log in" to do its job.

**Why a real home directory?** The agent needs a workspace for:
- Its binary and config
- Log files (`context.log.md`, `didactyl.log`)
- Any files it creates during shell operations
- The `working_directory` for the shell tool

### Step 2: Install the Binary and Config

```bash
# Copy the static binary
sudo cp didactyl_static_x86_64 /home/didactyl/didactyl
sudo chmod 755 /home/didactyl/didactyl

# Copy and configure genesis.jsonc
sudo cp genesis.jsonc /home/didactyl/genesis.jsonc

# CRITICAL: Lock down permissions on the config file (contains nsec private key)
sudo chmod 600 /home/didactyl/genesis.jsonc

# Set ownership
sudo chown -R didactyl:didactyl /home/didactyl/

# Protect the home directory from other users
sudo chmod 750 /home/didactyl/
```

### Step 3: Configure genesis.jsonc

Edit `/home/didactyl/genesis.jsonc` with the agent's identity, your admin pubkey, LLM credentials, and the shell working directory:

```jsonc
{
  "key": {
    "nsec": "nsec1..."                    // Agent's private key
  },

  "admin": {
    "pubkey": "npub1..."                  // YOUR public key
  },

  "dm_protocol": "nip04",

  "llm": {
    "provider": "openai",
    "api_key": "sk-...",
    "model": "gpt-4o-mini",
    "base_url": "https://api.openai.com/v1",
    "max_tokens": 512,
    "temperature": 0.7
  },

  "tools": {
    "enabled": true,
    "max_turns": 8,
    "shell": {
      "enabled": true,
      "timeout_seconds": 60,              // systemctl can be slow
      "max_output_bytes": 131072,         // journalctl output can be large
      "working_directory": "/home/didactyl"
    }
  },

  "api": {
    "enabled": true,
    "port": 8484,
    "bind_address": "127.0.0.1"           // Localhost only — do NOT expose
  },

  "startup_events": [
    {
      "kind": 10002,
      "content": "",
      "tags": [
        ["r", "wss://relay.damus.io"],
        ["r", "wss://relay.primal.net"]
      ]
    }
  ]
}
```

**Key settings for server maintenance:**

| Setting | Value | Why |
|---------|-------|-----|
| `shell.timeout_seconds` | `60` | `systemctl` and `journalctl` can take time |
| `shell.max_output_bytes` | `131072` (128KB) | Log output can be verbose |
| `shell.working_directory` | `/home/didactyl` | Agent's home — safe default CWD |
| `api.bind_address` | `127.0.0.1` | Never expose the admin API to the network |

### Step 4: Configure sudo Privileges

```bash
sudo visudo -f /etc/sudoers.d/didactyl
```

Add the following (adjust to your needs):

```sudoers
# /etc/sudoers.d/didactyl
# Didactyl agent — scoped system maintenance privileges

# Service management
didactyl ALL=(ALL) NOPASSWD: /usr/bin/systemctl status *
didactyl ALL=(ALL) NOPASSWD: /usr/bin/systemctl restart *
didactyl ALL=(ALL) NOPASSWD: /usr/bin/systemctl start *
didactyl ALL=(ALL) NOPASSWD: /usr/bin/systemctl stop *
didactyl ALL=(ALL) NOPASSWD: /usr/bin/systemctl enable *
didactyl ALL=(ALL) NOPASSWD: /usr/bin/systemctl disable *
didactyl ALL=(ALL) NOPASSWD: /usr/bin/systemctl is-active *
didactyl ALL=(ALL) NOPASSWD: /usr/bin/systemctl is-enabled *
didactyl ALL=(ALL) NOPASSWD: /usr/bin/systemctl list-units *
didactyl ALL=(ALL) NOPASSWD: /usr/bin/systemctl daemon-reload

# Log inspection
didactyl ALL=(ALL) NOPASSWD: /usr/bin/journalctl *

# Network diagnostics (if needed)
didactyl ALL=(ALL) NOPASSWD: /usr/sbin/lsof *
```

**Commands that do NOT need sudo** (the didactyl user can run these directly):

- `free -h` — memory usage
- `df -h` — disk usage
- `uptime` — load averages
- `top -bn1` — process snapshot
- `ps aux` — process list
- `cat /proc/cpuinfo` — CPU info
- `cat /proc/meminfo` — memory info
- `ss -tlnp` — listening ports (as unprivileged user, shows own processes)
- `uname -a` — kernel info
- `w` — who is logged in

### Step 5: Create the systemd Unit File

```bash
sudo tee /etc/systemd/system/didactyl.service << 'EOF'
[Unit]
Description=Didactyl Sovereign Nostr Agent
After=network-online.target
Wants=network-online.target

[Service]
Type=simple
User=didactyl
Group=didactyl
WorkingDirectory=/home/didactyl

ExecStart=/home/didactyl/didactyl --config /home/didactyl/genesis.jsonc --debug 3

# --- Privilege & Sandbox ---
# Must be false — sudo needs to escalate privileges
NoNewPrivileges=false

# Protect filesystem: read-only except for agent home
ProtectSystem=strict
ReadWritePaths=/home/didactyl

# Must be false — the agent's home IS its workspace
ProtectHome=false

# Isolate /tmp
PrivateTmp=yes

# --- Environment ---
Environment=SSL_CERT_FILE=/etc/ssl/certs/ca-certificates.crt

# --- Restart Policy ---
Restart=on-failure
RestartSec=10

# --- Logging ---
StandardOutput=journal
StandardError=journal
SyslogIdentifier=didactyl

[Install]
WantedBy=multi-user.target
EOF
```

**Important systemd notes:**

| Directive | Value | Reason |
|-----------|-------|--------|
| `NoNewPrivileges` | `false` | Required for `sudo` to work from `popen()` |
| `ProtectSystem` | `strict` | Makes `/usr`, `/boot`, `/etc` read-only |
| `ReadWritePaths` | `/home/didactyl` | Whitelist the agent's home for writes |
| `ProtectHome` | `false` | The agent lives in `/home/` — can't protect it from itself |
| `PrivateTmp` | `yes` | Isolates `/tmp` so other processes can't snoop |
| `SSL_CERT_FILE` | path to CA bundle | Required for TLS connections to relays and LLM API |

### Step 6: Enable and Start

```bash
# Reload systemd to pick up the new unit
sudo systemctl daemon-reload

# Enable auto-start on boot
sudo systemctl enable didactyl

# Start the agent
sudo systemctl start didactyl

# Verify it's running
sudo systemctl status didactyl

# Watch logs in real-time
sudo journalctl -u didactyl -f
```

### Step 7: Verify the Agent is Working

1. **Check systemd status:**
   ```bash
   sudo systemctl status didactyl
   ```
   Should show `active (running)`.

2. **Check logs for relay connections:**
   ```bash
   sudo journalctl -u didactyl --no-pager -n 50
   ```
   Look for relay connection messages and "EOSE" (End of Stored Events).

3. **Send a test DM via Nostr:**
   From your admin Nostr client, send an encrypted DM to the agent's npub:
   ```
   What is the server uptime?
   ```
   The agent should call `local_shell_exec` with `uptime` and reply with the result.

4. **Test sudo access:**
   ```
   What services are running? Use systemctl list-units --type=service --state=running
   ```

5. **Check the local API (from the server itself):**
   ```bash
   curl http://127.0.0.1:8484/api/context
   ```

---

## Updating the Agent

To update Didactyl to a new version:

```bash
# Stop the service
sudo systemctl stop didactyl

# Replace the binary
sudo cp didactyl_static_x86_64_new /home/didactyl/didactyl
sudo chown didactyl:didactyl /home/didactyl/didactyl
sudo chmod 755 /home/didactyl/didactyl

# Start the service
sudo systemctl start didactyl
```

The agent's identity, skills, and memory live on Nostr — replacing the binary doesn't lose any state.

---

## Expanding Privileges

The sudoers file is the single control point for what the agent can do with elevated privileges. To grant additional capabilities:

```bash
sudo visudo -f /etc/sudoers.d/didactyl
```

**Examples of additional privileges you might add:**

```sudoers
# Package management (careful!)
didactyl ALL=(ALL) NOPASSWD: /usr/bin/apt update
didactyl ALL=(ALL) NOPASSWD: /usr/bin/apt install *
didactyl ALL=(ALL) NOPASSWD: /usr/bin/apt upgrade -y

# Docker management
didactyl ALL=(ALL) NOPASSWD: /usr/bin/docker ps *
didactyl ALL=(ALL) NOPASSWD: /usr/bin/docker restart *
didactyl ALL=(ALL) NOPASSWD: /usr/bin/docker logs *

# Firewall inspection
didactyl ALL=(ALL) NOPASSWD: /usr/sbin/ufw status *
didactyl ALL=(ALL) NOPASSWD: /usr/sbin/iptables -L *

# Nginx/Apache config test
didactyl ALL=(ALL) NOPASSWD: /usr/sbin/nginx -t
didactyl ALL=(ALL) NOPASSWD: /usr/sbin/apachectl configtest
```

---

## Customizing the Agent's Personality for Server Maintenance

The agent's behavior is defined by its default skill content in `genesis.jsonc` (the `default_skill.content` field). For a server maintenance role, you should customize the soul/skill to include instructions like:

- What services it's responsible for monitoring
- How frequently to check (via triggered skills)
- What constitutes an alert-worthy condition
- How to format status reports
- Which `sudo` commands are available to it
- Escalation procedures (when to alert you vs. auto-fix)

This is a skill/prompt engineering task that can be done after the base installation is working.

---

## Quick Reference

### File Locations

| File | Path | Permissions |
|------|------|-------------|
| Binary | `/home/didactyl/didactyl` | `755 didactyl:didactyl` |
| Config | `/home/didactyl/genesis.jsonc` | `600 didactyl:didactyl` |
| Home directory | `/home/didactyl/` | `750 didactyl:didactyl` |
| systemd unit | `/etc/systemd/system/didactyl.service` | `644 root:root` |
| sudoers | `/etc/sudoers.d/didactyl` | `440 root:root` |

### Common Commands

```bash
# Service management
sudo systemctl start didactyl
sudo systemctl stop didactyl
sudo systemctl restart didactyl
sudo systemctl status didactyl

# Logs
sudo journalctl -u didactyl -f          # follow live
sudo journalctl -u didactyl --since today
sudo journalctl -u didactyl -n 100      # last 100 lines

# Check agent's local API
curl http://127.0.0.1:8484/api/context

# Edit sudo permissions
sudo visudo -f /etc/sudoers.d/didactyl

# Edit config (stop service first)
sudo systemctl stop didactyl
sudo -u didactyl nano /home/didactyl/genesis.jsonc
sudo systemctl start didactyl
```
