Special permissions (setuid, setgid, sticky bit) in Linux CLI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the setuid permission do on a Linux executable file?

The setuid permission allows a user to run the executable with the file owner's permissions, not the user's own permissions. This is often used to allow normal users to run programs with elevated privileges safely.

intermediate

How does the setgid permission affect files and directories?

For files, setgid makes the program run with the group ID of the file's group. For directories, new files created inside inherit the directory's group instead of the user's primary group.

beginner

What is the purpose of the sticky bit on a directory?

The sticky bit on a directory restricts file deletion inside it. Only the file owner, directory owner, or root can delete or rename files, even if others have write permission on the directory.

beginner

How can you set the setuid permission on a file using chmod?

Use the command: chmod u+s filename. This adds the setuid bit to the file's permissions.

advanced

What does the permission string rwsr-sr-t indicate?

It shows a file with setuid (s in user execute), setgid (s in group execute), and sticky bit (t in others execute) all set. This means the file runs with owner and group privileges, and the sticky bit is active on the directory or file.

What does the setuid bit do when set on an executable file?

A Changes the file's group ownership

B Runs the file with the file owner's permissions

C Prevents the file from being executed

D Runs the file with the user's own permissions

The setuid bit makes the executable run with the file owner's permissions, allowing privilege escalation in a controlled way.

What effect does the sticky bit have on a directory?

A Allows only file owners or root to delete files inside

B Prevents anyone from deleting files inside

C Allows anyone to delete files inside

D Changes the directory's group ownership

The sticky bit restricts file deletion inside the directory to the file owner, directory owner, or root.

How do you set the setgid bit on a directory named 'shared'?

A chmod o+s shared

B chmod u+s shared

C chmod +t shared

D chmod g+s shared

The setgid bit is set with 'chmod g+s' on the directory.

If a directory has setgid set, what happens to new files created inside?

A They inherit the directory's group ownership

B They inherit the user's primary group

C They become read-only

D They inherit the directory's owner

Setgid on a directory causes new files to inherit the directory's group ownership.

Which command shows special permissions like setuid, setgid, and sticky bit in the file listing?

A ls -lh

B ls -a

C ls -l (with special letters s or t in permissions)

D ls -l

The 'ls -l' command shows permissions, and special bits appear as 's' or 't' in the permission string.

Explain what setuid, setgid, and sticky bit permissions do in Linux and give a real-life example for each.

Think about who can run or delete files and with what permissions.

Describe how to set and verify the sticky bit on a directory and why it might be useful.

Focus on commands and the purpose of sticky bit in shared spaces.