fix(linux): fix_snmp installs snmpd without refreshing apt cache first

A fresh cloud image's apt cache is stale/effectively empty — installing
snmpd without an apt-get update first could fail outright or hang on
unreachable mirrors, and the install call wasn't guarded, so a timeout
propagated as an opaque unguarded exception instead of a clean failure
result.

Also adds a new apt_update_upgrade device action (apt-get update +
upgrade), used by netork's VM-provisioning bootstrap alongside the
existing fix_apt_proxy action to fully prep a freshly provisioned VM's
apt before installing anything on it.

napalm_linux/linux.py

@@ -1884,8 +1884,43 @@ class LinuxDriver(OSDriver):
             return self._action_fix_snmp()
         if action == "fix_apt_proxy":
             return self._action_fix_apt_proxy()
+        if action == "apt_update_upgrade":
+            return self._action_apt_update_upgrade()
         raise NotImplementedError(f"Unknown action: {action!r}")
 
+    def _action_apt_update_upgrade(self) -> DeviceActionResultDict:
+        """Refresh the apt cache and upgrade all packages (apt-based systems only)."""
+        if self._pkg_manager != "apt":
+            return {
+                "success": True,
+                "output": f"Skipped — package manager is {self._pkg_manager!r}, not apt.",
+            }
+
+        sudo_check = self._send("sudo -n true 2>&1 || echo __SUDO_NEEDS_PW__")
+        if "__SUDO_NEEDS_PW__" in sudo_check or "password is required" in sudo_check.lower():
+            if not self._sudo_password:
+                return {
+                    "success": False,
+                    "output": (
+                        "sudo requires a password on this device but none is configured in "
+                        "netOrk. Please add the sudo password to a Credential Profile assigned "
+                        "to this device, or configure passwordless sudo (NOPASSWD) for this user."
+                    ),
+                }
+
+        lines: list[str] = []
+        try:
+            out = self._sudo("apt-get update -y 2>&1", read_timeout=90)
+            lines.append(f"[update] {out.strip()[-300:]}")
+            out = self._sudo(
+                "DEBIAN_FRONTEND=noninteractive apt-get upgrade -y 2>&1", read_timeout=240
+            )
+            lines.append(f"[upgrade] {out.strip()[-300:]}")
+            return {"success": True, "output": "\n".join(lines)}
+        except Exception as exc:
+            lines.append(f"[error] {exc}")
+            return {"success": False, "output": "\n".join(lines)}
+
     def _action_fix_snmp(self) -> DeviceActionResultDict:
         """Install, configure and start snmpd with community 'public'."""
         lines: list[str] = []
@@ -1908,6 +1943,16 @@ class LinuxDriver(OSDriver):
         if not pkg_mgr:
             return {"success": False, "output": "Package manager not detected — cannot install snmpd."}
 
+        # Refresh the package index first — a freshly provisioned (or simply
+        # long-untouched) system's cache can be stale/empty, which makes the
+        # install below fail outright rather than just being slow.
+        if pkg_mgr == "apt":
+            try:
+                update_out = self._sudo("apt-get update -y 2>&1", read_timeout=90)
+                lines.append(f"[update] {update_out.strip()[-200:]}")
+            except Exception as exc:
+                lines.append(f"[warn] apt-get update failed: {exc}")
+
         # Install both snmpd (daemon) and snmp (client tools incl. snmpget for probing)
         install_cmd: dict[str, str] = {
             "apt":    "DEBIAN_FRONTEND=noninteractive apt-get install -y snmpd snmp 2>&1",
@@ -1918,8 +1963,12 @@ class LinuxDriver(OSDriver):
         }
         cmd = install_cmd.get(pkg_mgr)
         if cmd:
-            out = self._sudo(cmd, read_timeout=120)
-            lines.append(f"[install] {out.strip()[-200:]}")
+            try:
+                out = self._sudo(cmd, read_timeout=120)
+                lines.append(f"[install] {out.strip()[-200:]}")
+            except Exception as exc:
+                lines.append(f"[error] install failed: {exc}")
+                return {"success": False, "output": "\n".join(lines)}
 
         # 2. Determine the IP netOrk is connecting from by checking the established SSH connection
         netork_ip = ""