title: How to fix "update-alternatives: warning: forcing reinstallation of alternative /usr/bin/python3.8 because link group python3 is broken"?
body: <p>Working with Ubuntu 16.04.7 I was trying to make <code>python3.8</code> my default python version. I followed the instructions given <a href="http://ubuntuhandbook.org/index.php/2020/07/python-3-8-4-released-install-ubuntu-18-04-16-04/" rel="nofollow noreferrer">here</a>, but in the end the standard python version did not change. Whenever I run</p>
  <pre><code>python -V
  </code></pre>
  <p>the output was always</p>
  <pre><code>Python 3.7.9
  </code></pre>
  <p>Here is the output of <code>sudo update-alternatives --config python3</code>:</p>
  <pre><code>There are 2 choices for the alternative python3 (providing /usr/bin/python3).
  
    Selection    Path                Priority   Status
  ------------------------------------------------------------
  * 0            /usr/bin/python3.8   2         auto mode
    1            /usr/bin/python3.7   1         manual mode
    2            /usr/bin/python3.8   2         manual mode
  
  Press &lt;enter&gt; to keep the current choice[*], or type selection number:
  </code></pre>
  <p>When I select '0' I get the error:</p>
  <pre><code>update-alternatives: warning: forcing reinstallation of alternative /usr/bin/python3.8 because link group python3 is broken
  </code></pre>
  <p>The only close hit on google is another <a href="https://askubuntu.com/questions/1237441/i-broke-python-cant-install-any-package-with-apt-because-package-python3-is-n">SO entry</a> with no answers!</p>
  <p>So how can I fix this problem?</p>
  <p>Also, here is the output of <code>ls -l /usr/bin/python*</code>:</p>
  <pre><code>lrwxrwxrwx 1 root root      18 Oct 17  2019 /usr/bin/python -&gt; /usr/bin/python2.7
  lrwxrwxrwx 1 root root       9 Nov 24  2017 /usr/bin/python2 -&gt; python2.7
  -rwxr-xr-x 1 root root 3488528 Jul 21 19:57 /usr/bin/python2.7
  lrwxrwxrwx 1 root root      33 Jul 21 19:57 /usr/bin/python2.7-config -&gt; x86_64-linux-gnu-python2.7-config
  lrwxrwxrwx 1 root root      16 Nov 24  2017 /usr/bin/python2-config -&gt; python2.7-config
  -rwxr-xr-x 1 root root     306 Oct 24  2015 /usr/bin/python2-futurize
  -rwxr-xr-x 1 root root     310 Oct 24  2015 /usr/bin/python2-pasteurize
  lrwxrwxrwx 1 root root      25 Oct  5 08:59 /usr/bin/python3 -&gt; /etc/alternatives/python3
  -rwxr-xr-x 2 root root 4456208 Jul 19 22:14 /usr/bin/python3.5
  lrwxrwxrwx 1 root root      33 Jul 19 22:14 /usr/bin/python3.5-config -&gt; x86_64-linux-gnu-python3.5-config
  -rwxr-xr-x 2 root root 4456208 Jul 19 22:14 /usr/bin/python3.5m
  lrwxrwxrwx 1 root root      34 Jul 19 22:14 /usr/bin/python3.5m-config -&gt; x86_64-linux-gnu-python3.5m-config
  -rwxr-xr-x 2 root root 5074632 Aug 18 09:35 /usr/bin/python3.7
  -rwxr-xr-x 2 root root 5074632 Aug 18 09:35 /usr/bin/python3.7m
  -rwxr-xr-x 1 root root 5391992 Sep 26 00:51 /usr/bin/python3.8
  lrwxrwxrwx 1 root root      16 Mar 23  2016 /usr/bin/python3-config -&gt; python3.5-config
  lrwxrwxrwx 1 root root      10 Mar 23  2016 /usr/bin/python3m -&gt; python3.5m
  lrwxrwxrwx 1 root root      17 Mar 23  2016 /usr/bin/python3m-config -&gt; python3.5m-config
  lrwxrwxrwx 1 root root      16 Nov 24  2017 /usr/bin/python-config -&gt; python2.7-config
  lrwxrwxrwx 1 root root      58 Mar 25  2016 /usr/bin/pythontex -&gt; ../share/texlive/texmf-dist/scripts/pythontex/pythontex.py
  -rwxr-xr-x 1 root root     306 Mar 25  2016 /usr/bin/pythontex3
  </code></pre>