set timezone on Ubuntu

Ubuntu server uses UTC for the default timezone, this blog will guide
you if you wanna change the default timezone

first select your timezone interactively by using 'tzselect', you may
need 'sudo'
after that, we wanna make the change permanently

sudo cp /usr/share/zoneinfo/Asia/Shanghai /etc/localtime

finally we change 'UTC=yes' into 'UTC=no' in the file located at
'/etc/default/rcS'

now you have it done! do a 'date' for sure