Identity, Permissions and Access Controls
Linux security requires managing users, groups, sudo access, authentication, ownership, special permissions, ACLs, SELinux/AppArmor concepts, and least privilege.
How to study for CompTIA Linux+
Treat each Linux+ item as an administration decision: identify the subsystem, read evidence, choose a safe command, protect data, and verify the result.
Core concepts
Concept 1
Identity tasks should separate authentication, authorization, group membership, account state, and privilege escalation.
Exam cue: Check user, group, sudo rule, file mode, ACL, and security context.
Concept 2
Permissions combine user, group, other, special bits, ACLs, and security modules to decide effective access.
Exam cue: Use least privilege instead of broad root access.
Concept 3
Least privilege protects systems by granting the minimum access needed for the task.
Exam cue: Separate login failure from authorization failure.
Risk pitfalls and guardrails
Adding a user to a privileged group when a narrow sudo rule would work.
Guardrail: Avoid answers that use destructive commands too early, skip evidence, grant broad root access, ignore persistence, or close without verification.
Changing mode bits while ignoring ACLs or security context.
Guardrail: Avoid answers that use destructive commands too early, skip evidence, grant broad root access, ignore persistence, or close without verification.
Unlocking an account without understanding why it was locked.
Guardrail: Avoid answers that use destructive commands too early, skip evidence, grant broad root access, ignore persistence, or close without verification.
Memory anchors
User Account
A user account has identity attributes, shell, home directory, password state, and group memberships.
Group Membership
Group membership grants shared access and can affect login sessions after membership changes.
Sudo Rule
A sudo rule permits controlled privilege escalation without sharing the root password.
Least Privilege
Least privilege grants only the access needed for the approved task.
Setuid
The setuid bit runs an executable with the file owner's privileges and requires careful control.
Setgid
The setgid bit can run with group privileges or cause new files to inherit a directory group.
Sticky Bit
The sticky bit on shared directories limits deletion to file owners, directory owners, or root.
ACL
Access control lists add more granular permissions beyond basic owner, group, and other bits.
SELinux Context
An SELinux context can deny access even when ordinary file permissions appear correct.
Account Lock
An account lock prevents authentication and should be investigated before reversal.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
Local logins must enforce a password-quality module without editing every application separately. Which recommendation is BEST? The current evidence has been preserved.
Linux hosts must authenticate corporate identities from a central directory. Which action is MOST appropriate? The current evidence has been preserved.
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
What is Pass Harbor?
Completely free exam prep for 317 U.S. exams.
- Practice questions
- Flashcards
- Study guides
- Mock exams
- No registration
- No paywall
- Start instantly
“No more expensive exam prep. Quality study tools should be accessible to everyone.”