Do not forget rerun unlocker

If install new version of vmware, do not forget to run unlocker again, otherwise the MacOS (e,g, catalina ) cannot boot.

sudo without password

Disable sudo password for all the members of sudoers group.

sudo visudo and add this line:  

%sudo   ALL=(ALL:ALL) NOPASSWD:ALL

openconnect ssl vpn

sudo apt install openconnect
Run this command:

sudo openconnect https://au.twaren.net/staff --protocol=nc

Repeat duplicate items in legend in Matplotlb jupyter

In unbuntu 18.04 this is not an error, however, it will produce duplicated legend in ubuntu 20.04. According to https://stackoverflow.com/questions/19385639/duplicate-items-in-legend-in-matplotlib, if plot the same line type twice, then it will produce the same lengend for the same line.
Therefore, I have to break the oringial one line into two lines:

    ax.plot(x, yU, Label=i,linewidth=2, dashes=dst,color='black')
    ax.plot(x, yL, linewidth=2, dashes=dst,color='black')
NB, the legend is removed from the second line.