Add solution for dnf needs-restarting -f issue

docs/RPi/solutions/solutions.md

@@ -0,0 +1,97 @@
+---
+title: Solutions
+author: Funzi
+---
+
+# Solutions and Troubleshooting
+
+## `dnf` always claims to require a restart
+
+### Symptom
+
+Even though the system has been restarted recently, e.g., after a Kernel update, `dnf needs-restarting -r` always
+returns with exit code `1`.
+
+```
+# dnf needs-restarting -r
+Core libraries or services have been updated since boot-up:
+  * dbus
+  * dbus-daemon
+  * glibc
+  * linux-firmware
+  * systemd
+
+Reboot is required to fully utilize these updates.
+More information: https://access.redhat.com/solutions/27943
+```
+
+**This affects both Rocky Linux 8 and 9.** However,
+a [patch for 9.3 is to be released soon](https://github.com/rpm-software-management/dnf-plugins-core/pull/468).
+
+### Cause
+
+The `dnf` plugin uses the `mtime` of `/proc/1` which is set to start of epoch due to lack of RTC on Raspberry Pi. The
+correct system time is set later at boot once network connectivity is established and an NTP server is reachable.
+Compared to 1970, every package update is after the last reboot which causes the wrong result.
+
+### Solution
+
+Until 9.3 is released, or if the system is still on
+8.x, [the patch](https://github.com/rpm-software-management/dnf-plugins-core/pull/468/commits/b8132e1e04fb44c9ef8ab7dbcea2d2b3b920be2c)
+can be manually applied to all versions.
+
+```
+# patch /usr/lib/python3.6/site-packages/dnf-plugins/needs_restarting.py <<EOF
+--- a/plugins/needs_restarting.py
++++ b/plugins/needs_restarting.py
+@@ -34,6 +34,7 @@ import functools
+ import os
+ import re
+ import stat
++import time
+ 
+ 
+ # For which package updates we should recommend a reboot
+@@ -199,7 +200,28 @@ class ProcessStart(object):
+ 
+     @staticmethod
+     def get_boot_time():
+-        return int(os.stat('/proc/1').st_mtime)
++        """
++        We have two sources from which to derive the boot time. These values vary
++        depending on containerization, existence of a Real Time Clock, etc.
++        For our purposes we want the latest derived value.
++        - st_mtime of /proc/1
++             Reflects the time the first process was run after booting
++             This works for all known cases except machines without
++             a RTC - they awake at the start of the epoch.
++        - /proc/uptime
++             Seconds field of /proc/uptime subtracted from the current time
++             Works for machines without RTC iff the current time is reasonably correct.
++             Does not work on containers which share their kernel with the
++             host - there the host kernel uptime is returned
++        """
++
++        proc_1_boot_time = int(os.stat('/proc/1').st_mtime)
++        if os.path.isfile('/proc/uptime'):
++            with open('/proc/uptime', 'rb') as f:
++                uptime = f.readline().strip().split()[0].strip()
++                proc_uptime_boot_time = int(time.time() - float(uptime))
++                return max(proc_1_boot_time, proc_uptime_boot_time)
++        return proc_1_boot_time
+ 
+     @staticmethod
+     def get_sc_clk_tck():
+-- 
+2.41.0
+EOF
+```
+
+It is advisable to `version-lock` the plugin version until it's fixed upstream. On 8.x, that might be the only solutions
+if the patch is not backported to 8.x upstream.  
+**Use at your own risk!**
+
+```
+# dnf versionlock add python3-dnf-plugins-core
+```
+