feat: apt package priority troubleshooting

knowledge base/apt.md

@@ -8,6 +8,7 @@
 1. [Version pinning](#version-pinning)
 1. [Troubleshooting](#troubleshooting)
    1. [Fix a "Problem with MergeList" or "status file could not be parsed" error](#fix-a-problem-with-mergelist-or-status-file-could-not-be-parsed-error)
+   1. [A package is not upgraded to the release and/or version I pinned](#a-package-is-not-upgraded-to-the-release-andor-version-i-pinned)
 1. [Further readings](#further-readings)
 1. [Sources](#sources)
 
@@ -35,7 +36,7 @@ apt show 'vlc'
 apt depends 'ufw'
 
 # Install packages.
-sudo apt install 'nano' 'python3-zstd/stable'
+sudo apt install 'nano' 'python3-zstd/stable' 'gparted=0.16.1-1'
 
 # Remove packages.
 sudo apt remove 'dhclient' 'sudo'
@@ -63,6 +64,10 @@ sudo apt-mark showauto
 sudo apt-mark auto 'zsh' 'bash-completion'
 sudo apt-mark auto $(sudo apt-mark showmanual)
 
+# Check package priorities.
+apt-check policy
+apt-check policy 'boinc-client'
+
 # Reconfigure packages.
 sudo dpkg-reconfigure 'mariadb-server'
 sudo dpkg-reconfigure -p 'low' 'unattended-upgrades'
@@ -142,6 +147,53 @@ sudo rm -vrf '/var/lib/apt/lists/'*
 sudo apt update
 ```
 
+### A package is not upgraded to the release and/or version I pinned
+
+1. The effective priority of the package might be lower than expected.<br/>
+   Check the package's priority is the one you wanted **and** is higher than the release's one.
+
+   ```sh
+   $ apt-cache policy 'boinc-client'
+   boinc-client:
+   Installed: 7.16.16+dfsg-1
+   Candidate: 7.20.5+dfsg-1.1
+   Version table:
+      7.20.5+dfsg-1.1 990     <-- wanted candidate, with its pinned priority
+         490 http://deb.debian.org/debian testing/main arm64 Packages
+          -1 http://deb.debian.org/debian unstable/main arm64 Packages
+   *** 7.16.16+dfsg-1 500     <-- usable candidate, with its effective priority
+         500 http://deb.debian.org/debian bullseye/main arm64 Packages
+         100 /var/lib/dpkg/status
+   ```
+
+1. The package might depend on other packages which are not upgradable at the moment, i.e. their current version might be required by other packages.<br/>
+   Try installing/upgrading it specifying the desired release and version of the package:
+
+   ```sh
+   $ sudo apt upgrade boinc-client/testing
+   Reading package lists... Done
+   Building dependency tree... Done
+   Reading state information... Done
+   Selected version '7.20.5+dfsg-1.1' (Debian:testing, Debian:unstable [arm64]) for 'boinc-client'
+   Selected version '7.20.5+dfsg-1.1' (Debian:testing, Debian:unstable [arm64]) for 'libboinc7' because of 'boinc-client'
+   Selected version '2.36-9' (Debian:testing, Debian:unstable [arm64]) for 'libc6' because of 'libboinc7'
+   Selected version '3.0.8-1' (Debian:testing, Debian:unstable [arm64]) for 'libssl3' because of 'libboinc7'
+   Selected version '12.2.0-14' (Debian:testing, Debian:unstable [arm64]) for 'libstdc++6' because of 'libboinc7'
+   Calculating upgrade... Done
+   Some packages could not be installed. This may mean that you have
+   requested an impossible situation or if you are using the unstable
+   distribution that some required packages have not yet been created
+   or been moved out of Incoming.
+   The following information may help to resolve the situation:
+
+   The following packages have unmet dependencies:
+    libc-bin : Depends: libc6 (< 2.32) but 2.36-9 is to be installed
+    libc-dev-bin : Depends: libc6 (< 2.32) but 2.36-9 is to be installed
+    libc6-dbg : Depends: libc6 (= 2.31-13+rpt2+rpi1+deb11u5) but 2.36-9 is to be installed
+    libc6-dev : Depends: libc6 (= 2.31-13+rpt2+rpi1+deb11u5) but 2.36-9 is to be installed
+   E: Broken packages
+   ```
+
 ## Further readings
 
 - [Apt configuration]