New Script: dns-rescue.sh

Interactive recovery tool for the AdGuard-Home-only DNS setup.
Useful when AGH fails to start at boot and systemd-resolved is masked.

dns-rescue.sh

@@ -0,0 +1,114 @@
+#!/bin/bash
+
+# dns-rescue.sh — emergency DNS recovery on a machine where AdGuard Home is the
+# sole local resolver (systemd-resolved is masked). If AGH fails to start, this
+# machine has no DNS until you intervene. Run this script from a TTY login.
+#
+# Author: Justin Moore
+# Version: 0.1.0
+
+set -u
+
+RESOLV=/etc/resolv.conf
+FALLBACK=1.1.1.1
+
+require_root() {
+    if [[ $EUID -ne 0 ]]; then
+        echo "Re-running with sudo..."
+        exec sudo -E "$0" "$@"
+    fi
+}
+
+show_status() {
+    echo "=== /etc/resolv.conf ==="
+    cat "$RESOLV" 2>/dev/null || echo "(missing!)"
+    echo
+    echo "=== AdGuard Home service ==="
+    systemctl is-active adguardhome 2>&1 | head -1
+    systemctl is-enabled adguardhome 2>&1 | head -1
+    echo
+    echo "=== Last 15 AGH log lines (this boot) ==="
+    journalctl -u adguardhome -b --no-pager -n 15 2>&1 | tail -15
+    echo
+    echo "=== Port 53 listeners ==="
+    ss -lntu 2>/dev/null | awk '/:53 /{print}' | head -5
+    echo
+    echo "=== Masked resolved units ==="
+    systemctl is-enabled systemd-resolved.service systemd-resolved-varlink.socket systemd-resolved-monitor.socket 2>&1 | paste -d' ' - - - -
+}
+
+add_fallback_dns() {
+    if grep -q "nameserver $FALLBACK" "$RESOLV" 2>/dev/null; then
+        echo "$FALLBACK is already in $RESOLV — nothing to do."
+        return
+    fi
+    echo "nameserver $FALLBACK" >> "$RESOLV"
+    echo "Added fallback nameserver $FALLBACK to $RESOLV."
+    echo "Test:"
+    getent hosts archlinux.org && echo "  DNS now resolves."
+}
+
+restart_agh() {
+    systemctl restart adguardhome
+    sleep 1
+    systemctl is-active adguardhome
+    journalctl -u adguardhome -b --no-pager -n 10 | tail -10
+}
+
+unmask_resolved() {
+    cat <<MSG
+This rolls back the local-DNS setup partway:
+  - unmasks systemd-resolved + its varlink/monitor sockets
+  - starts systemd-resolved (will bind 127.0.0.53:53)
+  - does NOT change /etc/resolv.conf, NetworkManager dropin, or nsswitch.conf
+
+Use this if AGH itself is broken and you want resolved back as a stopgap.
+You will still need to point /etc/resolv.conf at 127.0.0.53 (or let NM regenerate it)
+to actually use resolved.
+
+MSG
+    read -rp "Proceed? [y/N] " ans
+    [[ "$ans" =~ ^[Yy]$ ]] || { echo "Cancelled."; return; }
+    systemctl unmask systemd-resolved.service systemd-resolved-varlink.socket systemd-resolved-monitor.socket
+    systemctl start systemd-resolved
+    systemctl status systemd-resolved --no-pager -n 5
+}
+
+menu() {
+    cat <<MENU
+
+DNS rescue menu:
+  1) Show DNS status (resolv.conf, AGH state, log, port 53)
+  2) Add $FALLBACK as a temporary fallback nameserver
+  3) Restart AdGuard Home and tail its log
+  4) Unmask + start systemd-resolved (heavier rollback)
+  5) Open editor on /etc/resolv.conf
+  q) Quit
+MENU
+    read -rp "> " choice
+    case "$choice" in
+        1) show_status ;;
+        2) add_fallback_dns ;;
+        3) restart_agh ;;
+        4) unmask_resolved ;;
+        5) "${EDITOR:-vi}" "$RESOLV" ;;
+        q|Q) exit 0 ;;
+        *) echo "Unknown choice." ;;
+    esac
+}
+
+require_root "$@"
+
+if [[ $# -gt 0 ]]; then
+    case "$1" in
+        status)    show_status ;;
+        fallback)  add_fallback_dns ;;
+        restart)   restart_agh ;;
+        unmask)    unmask_resolved ;;
+        *) echo "Usage: $0 [status|fallback|restart|unmask]   (no arg = interactive menu)"; exit 2 ;;
+    esac
+    exit 0
+fi
+
+show_status
+while true; do menu; done