Understanding and Using the su and sudo Commands on Linux

The tutorial begins by preparing test users on a Linux system using useradd and setting passwords with passwd , then shows how to switch to the new user or root with su .

ubuntu@VM-0-14-ubuntu:~$ su -
Password:          # enter root password
root@VM-0-14-ubuntu:~# useradd -m test_user
root@VM-0-14-ubuntu:~# passwd test_user
Enter new UNIX password: ...

It clarifies that su stands for "switch user" and compares the two invocation styles: su <user> (non‑login shell) and su - <user> (login shell), illustrating how environment variables like PWD differ between them.

# non‑login shell example
ubuntu@VM-0-14-ubuntu:~$ su
Password:          # root password
root@VM-0-14-ubuntu:/home/ubuntu# env | grep PWD
PWD=/home/ubuntu

# login shell example
ubuntu@VM-0-14-ubuntu:~$ su -
Password:          # root password
root@VM-0-14-ubuntu:~# env | grep PWD
PWD=/root

The article then introduces the -c option to execute a single command as another user without staying in that shell, e.g., su - -c "tail -n 4 /etc/shadow" .

ubuntu@VM-0-14-ubuntu:~$ su - -c "tail -n 4 /etc/shadow"
Password:          # root password
ubuntu:$1$fZKcWEDI$uwZ64uFvVbwpHTbCSgim0/:18352:0:99999:7:::
ntp:*:17752:0:99999:7:::
mysql:!:18376:0:99999:7:::

Next, it explains sudo ("super user do"), its typical usage to run commands with root privileges, and common shortcuts like sudo !! . It shows how sudo respects the /etc/sudoers configuration, allowing password‑less execution for users such as ubuntu .

# sudoers excerpt
root    ALL=(ALL:ALL) ALL
%admin  ALL=(ALL) ALL
%sudo   ALL=(ALL:ALL) ALL
ubuntu  ALL=(ALL:ALL) NOPASSWD: ALL

The guide demonstrates adding a new user ( test_user ) to /etc/sudoers so it can use sudo , then verifies the change with a command like sudo tail -n 3 /etc/shadow .

test_user ALL=(ALL:ALL) ALL   # added to sudoers
$ sudo tail -n 3 /etc/shadow
ntp:*:17752:0:99999:7:::
mysql:!:18376:0:99999:7:::
test_user:$6$.ZY1lj4m$ii0x9CG8h.JHlh6zKbfBXRuolJmIDBHAd5eqhvW7lbUQXTRS//...:18406:0:99999:7:::

Finally, it compares the security implications of using su - (requires the root password) versus sudo su - (uses the invoking user's password and is controlled via /etc/sudoers ), emphasizing that sudo provides finer‑grained, auditable privilege delegation.