Setting the root password of windows 10 Ubuntu subsystem

Windows 10 installs the Ubuntu subsystem. When it is opened for the first time, it will let the user set his or her own user name and password, but this newly created user is not root user.
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> Here’s how:
zhangyun@DESKTOP-J39LRR2:~$sudo passwd
sudo] password for zhangyun:
n>assword:
Retype>password:
passwd:
4 passwd: password updated successfully