diff --git a/src/main/resources/static/css/style.css b/src/main/resources/static/css/style.css
index 6c5e02f..cd8b953 100644
--- a/src/main/resources/static/css/style.css
+++ b/src/main/resources/static/css/style.css
@@ -17,6 +17,7 @@
   --warning:     #d7ba7d;
   --sidebar-w:   290px;
   --topbar-h:    52px;
+  --audio-bar-h: 64px;
 }
 
 *, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
@@ -589,6 +590,63 @@ a:hover { text-decoration: underline; }
   accent-color: var(--accent);
 }
 
+/* ============================================================
+   AUDIO BAR – barra fija inferior
+   ============================================================ */
+.audio-bar-fixed {
+  position: fixed;
+  bottom: 0;
+  left: 0;
+  right: 0;
+  min-height: var(--audio-bar-h);
+  background: var(--bg-alt);
+  border-top: 3px solid var(--accent);
+  box-shadow: 0 -2px 12px rgba(0,0,0,.4);
+  z-index: 100;
+  display: flex;
+  align-items: center;
+  flex-wrap: wrap;
+  gap: .6rem 1rem;
+  padding: .6rem 1.5rem;
+  transition: transform .3s ease;
+}
+.audio-bar-fixed.audio-bar-hidden {
+  transform: translateY(110%);
+  pointer-events: none;
+}
+.audio-bar-icon {
+  color: var(--accent);
+  font-size: 1rem;
+  flex-shrink: 0;
+}
+.audio-bar-title {
+  font-size: .75rem;
+  font-weight: 700;
+  color: var(--text-muted);
+  text-transform: uppercase;
+  letter-spacing: .06em;
+  flex-shrink: 0;
+}
+.audio-bar-controls {
+  display: flex;
+  flex-wrap: wrap;
+  align-items: center;
+  gap: .5rem;
+  flex: 1;
+}
+.audio-bar-item {
+  display: flex;
+  align-items: center;
+  gap: .5rem;
+}
+.audio-bar-fixed audio {
+  height: 32px;
+  accent-color: var(--accent);
+}
+body.has-audio-bar {
+  padding-bottom: var(--audio-bar-h);
+}
+
 /* ============================================================
    CUESTIONARIOS
    ============================================================ */
diff --git a/src/main/resources/static/js/curso.js b/src/main/resources/static/js/curso.js
index 99d5809..39c5895 100644
--- a/src/main/resources/static/js/curso.js
+++ b/src/main/resources/static/js/curso.js
@@ -115,20 +115,6 @@ function renderMarkdown(md, tema, bloque, bloqueId, temaNum) {
 
   const html = marked.parse(md);
 
-  const audioHtml = (tema.audios && tema.audios.length)
-    ? `<div class="tema-audio-bar">
-        <i class="fas fa-headphones"></i>
-        <span class="tema-audio-label">Escuchar este tema</span>
-        ${tema.audios.map(a => `
-        <div class="tema-audio-item">
-          ${tema.audios.length > 1 ? `<span class="tema-audio-tag">${a.label}</span>` : ''}
-          <audio controls preload="none">
-            <source src="${a.src}" type="audio/mpeg">
-          </audio>
-        </div>`).join('')}
-      </div>`
-    : '';
-
   const leyesHtml = (tema.leyes && tema.leyes.length)
     ? `<div class="tema-leyes-bar">
         <i class="fas fa-landmark"></i>
@@ -142,7 +128,6 @@ function renderMarkdown(md, tema, bloque, bloqueId, temaNum) {
     : '';
 
   document.getElementById('lesson-content').innerHTML = `
-    ${audioHtml}
     ${leyesHtml}
     <div class="md-body">${html}</div>
     <nav class="lesson-nav" aria-label="Navegación entre temas">
@@ -159,6 +144,65 @@ function renderMarkdown(md, tema, bloque, bloqueId, temaNum) {
 
   // Actualizar progress en topbar
   updateTopbarProgress(pos, total);
+
+  // Barra de audio fija
+  updateAudioBar(tema, bloqueId, temaNum);
+}
+
+// ── Audio bar fija (bottom) ───────────────────────────────────
+function updateAudioBar(tema, bloqueId, temaNum) {
+  const bar        = document.getElementById('audio-bar');
+  const titleEl    = document.getElementById('audio-bar-title');
+  const controlsEl = document.getElementById('audio-bar-controls');
+  if (!bar || !titleEl || !controlsEl) return;
+
+  // Parar cualquier audio en curso
+  bar.querySelectorAll('audio').forEach(a => a.pause());
+
+  if (!tema.audios || !tema.audios.length) {
+    bar.classList.add('audio-bar-hidden');
+    document.body.classList.remove('has-audio-bar');
+    return;
+  }
+
+  titleEl.textContent = `B${toRoman(bloqueId)} · T${temaNum}`;
+
+  controlsEl.innerHTML = tema.audios.map(a => `
+    <div class="audio-bar-item">
+      ${tema.audios.length > 1 ? `<span class="tema-audio-tag">${a.label}</span>` : ''}
+      <audio controls preload="none" data-key="audioPos:${a.src}">
+        <source src="${a.src}" type="audio/mpeg">
+      </audio>
+    </div>`).join('');
+
+  // Restaurar y guardar posición por audio
+  controlsEl.querySelectorAll('audio').forEach(audioEl => {
+    const key = audioEl.dataset.key;
+    audioEl.addEventListener('loadedmetadata', () => {
+      const saved = parseFloat(localStorage.getItem(key) || '0');
+      if (saved > 1 && saved < audioEl.duration - 2) {
+        audioEl.currentTime = saved;
+      }
+    });
+    let _saveTimer = null;
+    audioEl.addEventListener('play', () => {
+      clearInterval(_saveTimer);
+      _saveTimer = setInterval(() => {
+        localStorage.setItem(key, audioEl.currentTime.toString());
+      }, 5000);
+    });
+    audioEl.addEventListener('pause', () => {
+      clearInterval(_saveTimer);
+      localStorage.setItem(key, audioEl.currentTime.toString());
+    });
+    audioEl.addEventListener('ended', () => {
+      clearInterval(_saveTimer);
+      localStorage.removeItem(key);
+    });
+  });
+
+  bar.classList.remove('audio-bar-hidden');
+  document.body.classList.add('has-audio-bar');
 }
 
 function showError(msg) {
diff --git a/src/main/resources/temas/bloque4/B4T4.md b/src/main/resources/temas/bloque4/B4T4.md
index 5bf3648..4ec58c2 100644
--- a/src/main/resources/temas/bloque4/B4T4.md
+++ b/src/main/resources/temas/bloque4/B4T4.md
@@ -322,9 +322,7 @@ Mayor seguridad frente a ataques.
 
 ---
 
-## 8. Gestión de usuarios
-
-### 8.1. Introducción
+# 8. Gestión de usuarios
 
 La gestión de usuarios consiste en administrar:
 
@@ -388,7 +386,6 @@ Cada usuario debe tener:
 
 - Solo los permisos necesarios.
 
----
 
 ## Tipos de permisos
 
@@ -408,6 +405,15 @@ Ejecutar programas.
 
 Administración completa.
 
+## Linux/Unix
+- rwx (lectura, escritura, ejecución)
+- comandos: chmod, chown, chgrp
+## Windows
+- R (lectura)
+- W (escritura)
+- X (ejecución)
+- gestión mediante ACLs (Access Control Lists)
+
 ---
 
 # 11. Políticas de seguridad
diff --git a/src/main/resources/templates/curso.html b/src/main/resources/templates/curso.html
index daecff7..6fcc110 100644
--- a/src/main/resources/templates/curso.html
+++ b/src/main/resources/templates/curso.html
@@ -56,6 +56,13 @@
 
   </div>
 
+  <!-- ── Audio bar (fija, inferior) ──────────────────────── -->
+  <div id="audio-bar" class="audio-bar-fixed audio-bar-hidden" aria-label="Reproductor de audio">
+    <i class="fas fa-headphones audio-bar-icon"></i>
+    <span class="audio-bar-title" id="audio-bar-title"></span>
+    <div class="audio-bar-controls" id="audio-bar-controls"></div>
+  </div>
+
   <!-- ── Scripts ────────────────────────────────────────── -->
   <!-- marked.js para renderizar Markdown en el cliente -->
   <script src="https://cdn.jsdelivr.net/npm/marked@12/marked.min.js"></script>