Upgrade Ubuntu on WSL on Windows10

Windows10 was upgraded to 1803 at the end of April 2018. It seems that Windows Sybsystem for Linux (WSL) has been enhanced, and we will also upgrade WSL's Unbutu to the latest version.

Confirm version

Start up Ubuntu terminal and check the version.
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$ uname -a
Linux T470-S 4.4.0-17134-Microsoft #1-Microsoft Tue Apr 10 18:04:00 PST 2018 x86_64 x86_64 x86_64 GNU/Linux
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$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 16.04.3 LTS
Release: 16.04
Codename: xenial
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Local cache update

Update the local cache of the installed packages. In my environment, this setting prompted me to enter root's password.
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$ sudo apt update
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Update to latest version

Update the installed packages to the latest version.
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$ sudo apt upgrade
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I upgraded for the first time since installing Ubuntu on WSL in November 2017, and thus it took a considerable amount of time (over 10 minutes) to upgrade many packages. When the upgrade is finished, check the version again.
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$ uname -a
Linux T470-S 4.4.0-17134-Microsoft #1-Microsoft Tue Apr 10 18:04:00 PST 2018 x86_64 x86_64 x86_64 GNU/Linux
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$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 16.04.4 LTS
Release: 16.04
Codename: xenial
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