Linux Permissions 3 — Questions and Answers
Question 1: What octal value sets the setuid bit along with rwxr-xr-x permissions?
- 4755 (Correct answer)
- 2755
- 1755
- 6755
Correct answer: 4755
The setuid bit is represented by the leading 4 in octal, so 4755 means setuid + rwxr-xr-x.
Question 2: A user runs ls -l and sees -rwsr-xr-x on /usr/bin/passwd. What does the 's' in the owner execute position indicate?
- The setuid bit is set and the file is executable (Correct answer)
- The file is a symbolic link
- The setgid bit is set
- The sticky bit is active
Correct answer: The setuid bit is set and the file is executable
A lowercase 's' in the owner's execute position means the setuid bit is set and the owner execute bit is also set.
Question 3: Which command recursively changes permissions for all files and directories under /var/www to 755?
- chmod -R 755 /var/www (Correct answer)
- chmod -r 755 /var/www
- chown -R 755 /var/www
- chmod 755 -all /var/www
Correct answer: chmod -R 755 /var/www
The -R flag in chmod applies the permission change recursively to all files and subdirectories.
Question 4: What does ACL stand for in the context of Linux file permissions?
- Access Control List (Correct answer)
- Advanced Command Layer
- Application Control Logic
- Attribute Control Level
Correct answer: Access Control List
ACL stands for Access Control List, which allows more granular permission assignments beyond the traditional owner/group/other model.
Question 5: Which command is used to view the ACL entries on a file?
- getfacl file.txt (Correct answer)
- lsacl file.txt
- chmod -l file.txt
- stat --acl file.txt
Correct answer: getfacl file.txt
The `getfacl` command displays the access control list entries for a file or directory.
Question 6: A file is owned by user 'alice' and group 'staff'. User 'bob' is in the 'staff' group. The file has permissions rw-r-----. Can bob read the file?
- Yes, because bob is in the staff group which has read permission (Correct answer)
- No, because bob is not the owner
- Yes, because others have no permission which defaults to group
- No, because the file has no world-readable bits
Correct answer: Yes, because bob is in the staff group which has read permission
Bob belongs to the 'staff' group, which has read (r--) permission, so he can read the file.
Question 7: What permission mode does chmod 000 set on a file?
- Removes all read, write, and execute permissions for everyone (Correct answer)
- Sets full permissions for owner only
- Makes the file hidden
- Locks the file so only root can access it
Correct answer: Removes all read, write, and execute permissions for everyone
chmod 000 removes all permissions from owner, group, and others, making the file inaccessible to everyone except root.
Linux Permissions 3
What octal value sets the setuid bit along with rwxr-xr-x permissions?