Mark installed kernel packages as automatically installed.

usr/lib/linuxmint/mintUpdate/Classes.py

@@ -7,6 +7,7 @@
 import gettext
 import json
 import os
+import re
 import subprocess
 import sys
 import time
@@ -26,6 +27,22 @@
     'linux-modules-VERSION-KERNELTYPE', 'linux-modules-extra-VERSION-KERNELTYPE']
 KERNEL_PKG_NAMES.append('linux-image-extra-VERSION-KERNELTYPE') # Naming convention in 16.04, until 4.15 series
 
+# Matches the actual, version-specific kernel packages (linux-image-5.15.0-91-generic,
+# linux-headers-5.15.0-91, linux-modules-iwlwifi-6.8.0-41-generic, ...) as opposed to
+# meta packages (linux-generic, linux-generic-hwe-24.04, linux-virtual, ...), by
+# looking for an embedded VERSION-ABI kernel version rather than enumerating package
+# flavors. Meta package names never contain one (an HWE series suffix like
+# "-hwe-24.04" has no third version component or ABI number). Apt normally marks
+# versioned kernel packages as automatically installed when they're pulled in as a
+# dependency of a meta package, which is what lets "apt autoremove" clean up
+# superseded kernels. When mintupdate installs them directly by name (because no
+# meta package tracks that exact version, or via the kernel selection window), they
+# must be explicitly flagged the same way or they stick around forever.
+REAL_KERNEL_PKG_RE = re.compile(r'^linux-.*-\d+\.\d+\.\d+-\d+')
+
+def is_real_kernel_package(name):
+    return bool(REAL_KERNEL_PKG_RE.match(name))
+
 CONFIGURED_KERNEL_TYPE = settings.get_string("selected-kernel-type")
 if CONFIGURED_KERNEL_TYPE not in SUPPORTED_KERNEL_TYPES:
     CONFIGURED_KERNEL_TYPE = "-generic"

usr/lib/linuxmint/mintUpdate/kernelwindow.py

@@ -452,7 +452,11 @@ def install_kernels(self, kernels):
                                     continue
                                 to_purge.append(name)
                         else:
-                            to_install.append(name)
+                            # Flag it for aptkit as an automatic install so that
+                            # "apt autoremove" (and mintupdate's own obsolete-kernel
+                            # cleanup) can reclaim it once it's superseded, matching
+                            # how a normal kernel upgrade marks these packages.
+                            to_install.append(name + "#auto")
 
                     # Clean out left-over meta package
                     if kernel.installed:

usr/lib/linuxmint/mintUpdate/mintUpdate.py

@@ -33,7 +33,7 @@
 from kernelwindow import KernelWindow
 from preferences import PreferencesWindow
 
-from Classes import MainloopTimer, PRIORITY_UPDATES, UpdateTracker
+from Classes import MainloopTimer, PRIORITY_UPDATES, UpdateTracker, is_real_kernel_package
 from util import on_battery, _idle, _async, Inhibitor
 
 
@@ -2197,7 +2197,15 @@ def install(self, widget):
                    [True for pkg in update.package_names if "nvidia" in pkg]:
                    self.reboot_required = True
                 for package in update.package_names:
-                    self.packages.append(package)
+                    if update.type == "kernel" and is_real_kernel_package(package):
+                        # Flag it for aptkit as an automatic install (see aptkit's
+                        # _mark_packages_for_installation()), matching what a normal
+                        # "apt upgrade" would do when a meta package pulls in a new
+                        # kernel version. Otherwise apt records it as manually
+                        # installed and "apt autoremove" never cleans it up.
+                        self.packages.append(package + "#auto")
+                    else:
+                        self.packages.append(package)
                     self.logger.write("Will install " + str(package))
             iter = model.iter_next(iter)