Special permissions (setuid, setgid, sticky bit) in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of ls -l for a file with setuid bit set?

You run ls -l on a file with the setuid bit set. Which of the following shows the correct permission string for that file?

Linux CLI

ls -l /path/to/setuid_file

A -rwsr-xr-x 1 user group 1234 Apr 27 12:00 setuid_file

B -rwxr-sr-x 1 user group 1234 Apr 27 12:00 setuid_file

C -rwxr-xr-t 1 user group 1234 Apr 27 12:00 setuid_file

D -rwxr-xr-x 1 user group 1234 Apr 27 12:00 setuid_file

💡 Hint

Look for an 's' in the user execute position to indicate setuid.

The setuid bit replaces the user execute bit with 's' if execute is set, so the permission string shows 'rws' for the user part.

💻 Command Output

intermediate

What does the sticky bit do on a directory?

You set the sticky bit on a directory. What effect does it have on the directory's behavior?

Linux CLI

chmod +t /tmp/shared_dir
ls -ld /tmp/shared_dir

A Only the directory owner, file owner, or root can delete or rename files inside the directory.

B All users can delete or rename any files inside the directory regardless of ownership.

C The directory becomes read-only for all users except root.

D The directory allows execution of files inside it by all users.

💡 Hint

Think about shared directories like /tmp where many users write files.

The sticky bit on directories restricts deletion or renaming of files to the file owner, directory owner, or root, preventing others from deleting files they don't own.

📝 Syntax

advanced

Which chmod command sets the setgid bit on a directory?

You want to set the setgid bit on a directory named project. Which command correctly does this?

A chmod o+s project

B chmod +s project

C chmod g+s project

D chmod u+s project

💡 Hint

The setgid bit is related to the group permissions.

The setgid bit is set using 'g+s' with chmod, which applies the setgid bit to the group permissions.

🚀 Application

advanced

What is the effect of setgid on a directory's new files?

You set the setgid bit on a directory. What happens to the group ownership of new files created inside that directory?

A New files inherit the user's primary group, ignoring the directory's group.

B New files inherit the group ownership of the directory, not the user's primary group.

C New files have no group ownership set.

D New files inherit the group ownership of the parent directory's parent.

💡 Hint

Think about how group collaboration is managed in shared directories.

When the setgid bit is set on a directory, new files created inside inherit the directory's group ownership, facilitating group collaboration.

🧠 Conceptual

expert

What error occurs if a non-root user tries to set the setuid bit on a file they own?

A user tries to run chmod u+s myscript.sh on a file they own but is not root. What happens?

Linux CLI

chmod u+s myscript.sh

A File becomes unreadable due to permission conflict.

B The setuid bit is set successfully without errors.

C Syntax error because setuid bit cannot be set with chmod.

D Permission denied error because only root can set setuid bit.

💡 Hint

Consider who has the privilege to set special permission bits.

Only the root user can set the setuid bit on files. Non-root users get a permission denied error.