LFCS Essential Commands Practice Question
Which THREE of the following statements about Linux file permissions are correct?
⚠ Common exam trap
A common mix-up: candidates confuse the numeric permission values (e.g., thinking 644 gives rw-rw-rw- instead of rw-r--r--) or misinterpret the symbolic mode syntax, such as assuming 'a+w' removes write permission when it actually adds it.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The command 'chmod 400 secret.txt' sets read-only permission for the owner only.
The numeric permission mode 400 corresponds to read (4) for the owner, with no permissions for the group or others (0 and 0). This sets the file's permissions to r--------, meaning only the owner can read the file, and no one can write or execute it.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The command 'chmod a+w file' removes write permission for all.
Why it's wrong here
a+w adds write permission; a-w removes it.
- ✓
The command 'chmod 400 secret.txt' sets read-only permission for the owner only.
Why this is correct
400 is r-------- (owner read only).
- ✓
The command 'chmod 755 file' sets permissions to rwxr-xr-x.
Why this is correct
755 corresponds to rwx for owner, r-x for group and others.
- ✓
The command 'chmod u+x script.sh' adds execute permission for the owner.
Why this is correct
u+x adds execute for the user (owner).
- ✗
The command 'chmod 644 file' sets permissions to rw-rw-rw-.
Why it's wrong here
644 sets rw-r--r--, not rw-rw-rw-.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This LFCS practice question is part of Courseiva's free Linux Foundation certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the LFCS exam.