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
The 755 mode sets read and execute for group and other, and read, write and execute for the owner, so execute is granted to all three classes, not the owner alone. It is tempting because the leading 7 does include owner execute, and the command would be correct if the intent were to give only the owner execute while restricting group and other to read.
- ✗
Remove write permission for others
Why it's wrong here
Mode 755 grants owner rwx, group r-x and others r-x; others already lack write, so this describes a state the command produces incidentally, not its purpose. It tempts because 755 is commonly chosen precisely to stop others writing, but that is a side effect of the octal value, not the command's function.
- ✗
Set the setuid bit
Why it's wrong here
755 sets no setuid bit; setuid requires the 4000 octal digit, as in 4755. The option tempts because setuid binaries such as passwd are often also mode 755, so the two appear together, yet 755 alone never sets that bit.
- ✓
Set permissions to rwxr-xr-x
Why this is correct
Numeric mode 755 grants the owner read, write and execute (7), and group and others read and execute (5), producing rwxr-xr-x. This satisfies the requirement to translate the octal permission value into its symbolic equivalent.
Go deeper
Related to this question
About these practice questions
One of 406 original LFCS practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →
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.