Usage and differences of "Linux" Su, sudo, sudo su, sudo-i

sudo: temporarily switch to Superuser mode to perform superuser privileges, prompting for a password that is the current user's password, not the password for the super account. However there is a time limit, Ubuntu defaults to 15 minutes for one time.
SU: Switch to a certain user mode, prompted to enter the password when the password is Switched account password, the use of "SU account name." If the system defaults to the root account when no account is added, the password is also the password for the super account. There is no time limit.
Sudo-i: You can use this command to frequently perform certain permissions that only the superuser can perform, without having to enter the password each time. When prompted for a password, the password is the password for the current account. There is no time limit. After executing the command, the prompt changes to "#" instead of "$". You can perform "exit" or "logout" when you want to return a regular account.


Sudo-i directly run the sudo command plus-i parameter
sudo su runs the sudo command to give the SU command a right to run the SU command.
Sudo-i Running Results pwd=/root
sudo su run result pwd=/home/user name (current user home directory)

Usage and differences of "Linux" Su, sudo, sudo su, sudo-i