sudo and su

Created: February 19, 2020

sudo

sudo -s: opens an interactive non-login shell.

Only bashrc files are executed. Doesn’t change working directory.
sudo -i: opens an interactive login shell.
Profile files are executed.
Usually profile files source the contents of bashrc files as well.
As a profile file is executed, will change working directory to /root/ and change environment variables, including $PATH.
Nevertheless, there may be something useful or necessary set in the profile file.

The real and effective uid and gid of the issuing user are then set to match those of the target user account as specified in the passwd file.
The sudoers config file is /etc/sudoers and must be edited with visudo.
sudo suand sudo su - are bad practice because subsequent commands log as root, rather than per user, the root user has to be enabled, and they launch an additional process.
su: switch user.
sudo’s name: “su” + “do” = sudo

-V: version. When root, prints out the default sudo was compiled with, as well as the local machine’s IP addresses.
-l: list allowed and forbidden commands for the invoking user.
-v: extend the sudo timeout. The default timeout extension is 5 minutes.
-k: revoke (kill) sudo privileges by resetting the sudo timestamp.
-K: revoke (surekill) sudo privileges by removing the sudo timestamp.
-b: run in the background. Cannot control the process with the usual job control processes.
-p: override the default password prompt. See sudo man page.

A login shell is one whose first character of argument zero is a -, or one started with the –login option.
An interactive shell is one started without non-option arguments. This is a simplication.
/etc/bash.bashrc and ~/.bashrc are processed for interactive shells (that aren’t login shells).
/etc/profile, ~/.bash_profile, ~/.bash_login, and ~/.profile are only processed for login shells.

By convention, a profile file sources the corresponding bashrc as well, otherwise bashrc contents would not be processed for login shells.
The contents of ~/.bash_logout is executed on logout.
Shells launched by a terminal emulator are usually interactive.
If su [USER] is used, then this is an interactive shell and .bash_profile will not be processed.
If su - [USER] is used, then this is a login shell; .bash_profile will be processed. This will also cause the shell to use USER’s $PATH because .bash_profile sets $PATH.
This is a simplication and missing some detail. Further reading: the man bash INVOCATION section.

su: opens an interactive non-login shell. Read sudo -s section for implications.
su -: opens an interactive login shell. Read sudo -i section for implications.