sudo = POWER!! (managing users in Linux) // Linux for Hackers // EP4

Brief summary

Hands-on tutorial (Linux for Hackers, Ep.4) covering Linux user and group management using a browser lab from Hack The Box Academy. An Avengers/Thanos story is used as a narrative device to demonstrate creating, modifying, and deleting users/groups and granting sudo (superuser) privileges.

Core technical concepts

• Users and accounts
  • Linux represents accounts in /etc/passwd. Password hashes are stored in /etc/shadow.
• UIDs and GIDs
  • Numeric user ID (UID) and primary group ID (GID) are recorded in /etc/passwd.
• Home directories and default shells
  • User home directories typically live at /home/username. Login shell examples: /bin/bash.
• adduser vs useradd
  • adduser is interactive and prompts for details.
  • useradd is more minimal/non-interactive but accepts flags for behavior.
• Password management
  • passwd username to set or change a user’s password.
• Modifying accounts
  • usermod can change shell, rename users, and append supplemental groups.
• Groups and /etc/group
  • Create groups, inspect membership, and assign privileges by group membership.
• sudo vs su
  • sudo (“super user do”) runs a single command with elevated privileges.
  • su switches user accounts (requires the target user’s password unless using sudo).
• Sudoers and visudo
  • /etc/sudoers defines who can use sudo. Edit with visudo to avoid syntax errors.
  • Group-based sudo (e.g., %sudo) and NOPASSWD options are commonly used.
• Principle of least privilege
  • Grant sudo rights only when necessary and remove privileges when finished.

Best practices: - Don’t routinely log in as root; prefer sudo. - Use visudo to edit the sudoers file to avoid breaking sudo with syntax errors. - Follow the principle of least privilege when granting access.

Commands and flags (quick reference)

• whoami — show current user
• cat /etc/passwd — list users and account fields
• sudo cat /etc/shadow — view hashed passwords (requires root)
• adduser username — interactive user creation
• useradd username — non-interactive user creation
• useradd -m username — create user and home directory
• passwd username — set/change password
• usermod --shell /bin/bash username — change default shell
• usermod -l newname oldname — rename user
• usermod -aG groupname username — append user to supplemental group
• su - username — switch to another user (requires that user’s password)
• sudo su - — become root (uses your sudo privilege)
• sudo visudo (or sudo vi /etc/sudoers) — edit sudoers file safely (visudo recommended)
• sudo userdel username — delete user
• sudo groupadd groupname — create group
• cat /etc/group — view groups and memberships
• sudo gpasswd -d username groupname — remove user from group
• sudo groupdel groupname — delete a group

Tutorial / guide elements & resources

• Live demo available in a free Hack The Box Academy browser lab (Linux Fundamentals → User Management module).
• Step-by-step actions demonstrated:
  1. Create users (e.g., Thor, Iron Man), set passwords.
  2. Inspect /etc/passwd and /etc/shadow.
  3. Create groups and view /etc/group.
  4. Edit sudoers to grant sudo rights to a group.
  5. Add/remove users to/from groups.
  6. Delete users and groups.
• Advice reiterated throughout:
  • Prefer sudo over logging in as root.
  • Use visudo for editing /etc/sudoers.
  • Remove elevated privileges when they are no longer needed.
• Additional materials:
  • HTB Academy course page includes a command summary and a quiz.
  • Video description links to a free quiz and the HTB Academy lab.
  • HTB Academy offers a student subscription and some modules provide CPE credits.

Main speakers / sources

• Video presenter: host of the “Linux for Hackers” series, who demonstrates commands and concepts.
• Hack The Box Academy: sponsor and provider of the browser-based Linux lab and course materials.