Chapter 3: Linux Basic Commands
3.6 Users, groups and sudo
| Command | Purpose |
|---|---|
whoami |
Current user name |
id |
UID, GID and groups of the current user |
sudo useradd -m -s /bin/bash ravi |
Create user with home dir and bash shell (adduser ravi on Ubuntu is interactive) |
sudo passwd ravi |
Set password |
sudo usermod -aG wheel ravi |
Add to admin group (wheel on AL2023/CentOS, sudo on Ubuntu) |
sudo groupadd devops |
Create group |
sudo usermod -aG devops ravi |
Add user to extra group (-a = append — never forget it!) |
groups ravi |
Show user's groups |
sudo userdel -r ravi |
Delete user and home folder |
su - ravi |
Switch to another user |
sudo -i |
Become root (use carefully, type exit to return) |
User information lives in /etc/passwd (accounts), /etc/shadow (hashed passwords) and /etc/group (groups). Sudo rules live in /etc/sudoers — always edit with sudo visudo.
Why sudo instead of logging in as root?
sudo gives admin power only for one command, logs who did what (/var/log/secure or /var/log/auth.log), and reduces accidents. On EC2, the default user (ec2-user/ubuntu) has password-less sudo, and direct root login over SSH is disabled.