Which chmod command sets owner read/write/execute and group/others read/execute on a file named secret.txt?

• A. chmod 754 secret.txt
• B. chmod 755 secret.txt
• C. chmod 777 secret.txt
• D. chmod 644 secret.txt

Answer: (B)

This question tests how file permissions map to the three-digit octal mode used by chmod. Each digit represents a class: owner, group, and others, and the digit is the sum of permission bits: read is 4, write is 2, execute is 1. You want the owner to have read, write, and execute, which equals 7 (4+2+1). You want the group and others to have read and execute, which equals 5 (4+1) for each. Put together, that gives 755. Therefore, the command to set those permissions on secret.txt is chmod 755 secret.txt. The other options don’t match this exact pattern: 754 would give others only read (no execute); 777 would grant all permissions to everyone (more permissive than required); 644 would give no execute permission to anyone.