What Does chmod 755 Mean?
Network Topology
What is the purpose of the chmod 755 command in this exhibit?
Quick Answer
The answer is that chmod 755 sets file permissions to rwxr-xr-x. This octal value breaks down as 7 (4+2+1) for the owner, granting read, write, and execute, while the 5 (4+1) for both group and others gives only read and execute. This configuration is correct because it allows the owner full control to modify the file, while preventing non-owners from writing to it—a standard security practice for executable scripts and directories. On the Linux Foundation Certified System Administrator LFCS exam, this command tests your understanding of octal permission notation and the principle of least privilege; a common trap is confusing the 5 (read+execute) with 4 (read-only) or 6 (read+write). Remember the mnemonic: 7 is the owner’s full set, and 5 is the “safe execute” for everyone else—like a 5-star rating for read and execute only.
⚠ Common exam trap
Many exam-takers confuse the octal value 755 with adding execute only for the owner (option A) or think it removes write for others (option B), when in fact 755 sets a specific permission mask that includes execute for all and write only for the owner.
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
✓
Set permissions to rwxr-xr-x
The chmod 755 command sets the file permissions to rwxr-xr-x, meaning the owner has read, write, and execute permissions (7), while the group and others have read and execute permissions (5). This is a common permission set for executable scripts and directories to allow execution without granting write access to non-owners.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Add execute permission for the owner only
Why it's wrong here
755 adds execute for all, not just owner.
- ✗
Remove write permission for others
Why it's wrong here
Others already had read-only; 755 does not remove write because they had none.
- ✗
Set the setuid bit
Why it's wrong here
chmod 755 does not set setuid; that would be 4755.
- ✓
Set permissions to rwxr-xr-x
Why this is correct
755 corresponds to rwxr-xr-x.
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Same concept, more angles
1 more way this is tested on LFCS
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A user wants to set the permissions of a file to 'rwxr-xr--'. Which octal permission value should they use with chmod?
easy- ✓ A.754
- B.755
- C.644
- D.744
Why A: The permissions 'rwxr-xr--' mean that the owner has read, write, and execute (rwx = 7), the group has read and execute (r-x = 5), and others have only read (r-- = 4). Therefore, the correct octal value is 754. Option A is correct. Option B (755) gives others execute, option C (644) gives owner no execute and group no execute, and option D (744) gives group no execute.
JA
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.