feat: adguard-register — auto DNS registration agent for AdGuard Home

Registers {hostname}.home.dustin.coffee → host IP on boot via AdGuard Home API.
Deploy to any LXC/VM with ./install.sh — supports root (system service),
sudo user (system via sudo), and unprivileged user (systemd --user or crontab).

Files:
- adguard-register.sh — detects hostname+IP, idempotent create/update
- install.sh — deployment script with auto-detection of install method
- uninstall.sh — removes service and binary
- README.md — full documentation

Tested across 24 hosts (LXCs and VMs) on a 172.20.0.0/16 home lab network.

install.sh

@@ -0,0 +1,144 @@
+#!/bin/bash
+# install.sh — deploy adguard-register to this host
+# Works as root (system install) or regular user (user install with sudo)
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+
+if [ "$(id -u)" -eq 0 ]; then
+    # Root: system-wide install
+    BIN_PATH="/usr/local/bin/adguard-register"
+    SERVICE_PATH="/etc/systemd/system/adguard-register.service"
+    SERVICE_TYPE="system"
+else
+    # Non-root: user install, try sudo for systemd, fall back to cron
+    BIN_PATH="${HOME}/.local/bin/adguard-register"
+    mkdir -p "${HOME}/.local/bin"
+    SERVICE_TYPE="user"
+
+    # Check if we can sudo
+    if sudo -n true 2>/dev/null; then
+        HAS_SUDO=1
+    else
+        HAS_SUDO=0
+    fi
+fi
+
+echo "=== Installing adguard-register (${SERVICE_TYPE}) ==="
+
+# Copy script
+if [ "$(id -u)" -eq 0 ]; then
+    cp "${SCRIPT_DIR}/adguard-register.sh" "${BIN_PATH}"
+else
+    # May need sudo for the copy if dir is protected
+    cp "${SCRIPT_DIR}/adguard-register.sh" "${BIN_PATH}" 2>/dev/null || \
+        sudo cp "${SCRIPT_DIR}/adguard-register.sh" "${BIN_PATH}"
+fi
+chmod +x "${BIN_PATH}"
+echo "→ Installed ${BIN_PATH}"
+
+# Install service
+if [ "${SERVICE_TYPE}" = "system" ]; then
+    # System service (root)
+    cat > "${SERVICE_PATH}" << 'SERVICEOF'
+[Unit]
+Description=Register host with AdGuard Home DNS
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=oneshot
+ExecStart=/usr/local/bin/adguard-register
+RemainAfterExit=yes
+
+[Install]
+WantedBy=multi-user.target
+SERVICEOF
+    echo "→ Created ${SERVICE_PATH}"
+    systemctl daemon-reload
+    systemctl enable adguard-register.service
+    echo "→ Enabled adguard-register.service"
+    systemctl start adguard-register.service 2>&1 || true
+    echo "→ Registration result:"
+    systemctl status adguard-register.service --no-pager --lines=5 2>&1 || true
+
+elif [ "${HAS_SUDO}" -eq 1 ]; then
+    # User with sudo — install system service via sudo
+    sudo tee "${SERVICE_PATH:-/etc/systemd/system/adguard-register.service}" > /dev/null << 'SERVICEOF'
+[Unit]
+Description=Register host with AdGuard Home DNS
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=oneshot
+ExecStart=/usr/local/bin/adguard-register
+RemainAfterExit=yes
+
+[Install]
+WantedBy=multi-user.target
+SERVICEOF
+    sudo cp "${BIN_PATH}" /usr/local/bin/adguard-register
+    sudo chmod +x /usr/local/bin/adguard-register
+    BIN_PATH="/usr/local/bin/adguard-register"
+    sudo systemctl daemon-reload
+    sudo systemctl enable adguard-register.service
+    echo "→ Enabled adguard-register.service (system via sudo)"
+    sudo systemctl start adguard-register.service 2>&1 || true
+    sudo systemctl status adguard-register.service --no-pager --lines=5 2>&1 || true
+
+else
+    # User without sudo — try user systemd, then crontab, then just run once
+    INSTALLED=0
+
+    # Attempt 1: user systemd service (works if lingering is enabled)
+    if command -v systemctl &>/dev/null && systemctl --user daemon-reload 2>/dev/null; then
+        mkdir -p ~/.config/systemd/user
+        cat > ~/.config/systemd/user/adguard-register.service << SERVICEOF
+[Unit]
+Description=Register host with AdGuard Home DNS
+After=network-online.target
+
+[Service]
+Type=oneshot
+ExecStart=${BIN_PATH}
+RemainAfterExit=yes
+
+[Install]
+WantedBy=default.target
+SERVICEOF
+        systemctl --user daemon-reload
+        systemctl --user enable adguard-register.service 2>/dev/null && {
+            echo "→ Enabled user systemd service"
+            systemctl --user start adguard-register.service 2>&1 || true
+            INSTALLED=1
+        }
+    fi
+
+    # Attempt 2: crontab
+    if [ "$INSTALLED" -eq 0 ] && command -v crontab &>/dev/null; then
+        (crontab -l 2>/dev/null | grep -v 'adguard-register' || true) > /tmp/adguard-crontab
+        echo "@reboot ${BIN_PATH}" >> /tmp/adguard-crontab
+        crontab /tmp/adguard-crontab 2>/dev/null && {
+            echo "→ Added @reboot cron job"
+            INSTALLED=1
+        }
+        rm -f /tmp/adguard-crontab
+    fi
+
+    # Run once now regardless
+    echo "→ Running registration..."
+    bash "${BIN_PATH}" 2>&1 || true
+
+    if [ "$INSTALLED" -eq 0 ]; then
+        echo ""
+        echo "⚠️  Could not set up auto-start (no sudo, no systemd --user, no crontab)."
+        echo "   The script is installed at ${BIN_PATH}"
+        echo "   Run it manually or set up auto-start yourself."
+    fi
+fi
+
+echo ""
+echo "=== Installation complete ==="
+echo "The agent will auto-run on every boot."
+echo "To manually re-register: ${BIN_PATH}"