事出有因

 I assumed that I install verilator via git clone its source, so I need to set the export VERILATOR_ROOT.

At first, due to laziness, I just copy the code directly to my ubuntu. 

 so stupid I am!!!

Then, I recoginzed that the pathname is not real, but a prompt...

Therefore, from the error message, I correct it from the pathname.

It failed eventually, maybe default path is not that.

怎么补救

If you do the same to me, look here:

unset VERILATOR_ROOT

Read the page again, I saw "make install"....

All is due to innocence, so keep learning.