Upgrade to Ubuntu 20.04 Focal on WSL1 and WSL2

Upgrade to Ubuntu 20.04 Focal on WSL (aka WSL1) and WSL2 instructions.md

1. Display whether you have WSL1 or WSL2 by typing wsl --list --verbose into a PowerShell prompt, like this:

   PS C:\Users\mslin> wsl --list --verbose
     NAME      STATE           VERSION
   * Ubuntu    Running         1
   

   The above shows that a machine has WSL1 installed.
2. Ignore this step if you have WSL2.
   
   The default Ubuntu sleep command does not work on WSL1. sleep must work properly in order for the upgrade to succeed. To fix the problem, replace /bin/sleep with an equivalent Python 3 program prior to running do-release-upgrade. This will avoid the problem sleep: cannot read realtime clock: Invalid argument described in this askubuntu posting. To do this, type:

   $ sudo mv /bin/sleep{,-}  # renames sleep to sleep-
   $ sudo vi /bin/sleep     # I use vi, but you can use any editor with sudo

   Enter the code for /bin/sleep shown below using your favorite editor:

   #!/usr/bin/env python3
   
   import sys
   import time
   
   time.sleep(int(sys.argv[1]))

   Save the file. Now make your replacement for sleep executable:

   $ sudo chmod a+x /bin/sleep

3. Ensure that all previous upgrades have been applied:

   $ sudo apt upgrade

4. Verify that the last line of /etc/update-manager/release-upgrades is Prompt=normal. If not, edit with your favorite editor:

   $ sudo vi /etc/update-manager/release-upgrades

5. Run the upgrade. Because Ubuntu rolls out its upgrade to users gradually, you might have to try this several times over a few days. Some of my machines update earlier than others, even though they are in the same building. You may find instructions elsewhere that advocate "Force direct upgrade by using the -d switch". This is incorrect. There is no such thing as a direct upgrade, instead the -d switch installs a development version, which means you will forever after install a whole lot of prerelease software. Don't do that unless you have a good reason. This is what most users should type:

   $ sudo do-release-upgrade

6. The installation will die after a while with the following error:

   dpkg: error processing package libc6:amd64 (--configure):
   installed libc6:amd64 package post-installation script subprocess returned error exit status 1
   Errors were encountered while processing:
   libc6:amd64
   

   To fix the problem (from https://stackoverflow.com/a/61697214/553865) edit /var/lib/dpkg/info/libc6\:amd64.postinst and comment out this line near the top of the file:

   set -e
   

   so it looks like this:

   # set -e
   

   Now type:

   $ apt-get -f install

7. To conclude the upgrade, type:

   $ sudo apt upgrade --fix-missing
   $ sudo apt upgrade
   $ sudo apt-get dist-upgrade -y
   $ sudo apt autoremove
   $ sudo apt autoclean