MODULE 18- Special directories and files

Question 1

What happens when the setuid permission is set on an executable binary file?

Answer 1

→ The file is executed with the permissions of the file owner, not the user who runs it.

Question 2

What does a lowercase “s” in the file permissions (e.g., rwsr-xr-x) indicate?

Answer 2

→ It indicates that the setuid permission is set and the execute permission is also set for the user.

Question 2

Which symbolic command would you use to add the setuid permission to a file?

Answer 2

→ chmod u+s file

Question 2

Why is setuid used on certain system utilities like passwd?

Answer 2

→ It allows normal users to run these utilities with root privileges to access files like /etc/shadow.

Question 2

What does an uppercase “S” in the file permissions (e.g., rwSr-xr-x) indicate?

Answer 2

→ It indicates that the setuid permission is set but the execute permission for the user is not set.

Question 2

What happens when a directory with the setgid permission creates another directory?

Answer 2

→ Any new directory created within a setgid directory will inherit the setgid permission, meaning it will also be owned by the group that owns the parent directory.

Question 2

How do you remove the setuid permission using the symbolic method?

Answer 2

→ chmod u-s file

Question 2

How would you add the setuid permission numerically, given that the original file permissions are 775?

Answer 2

→ chmod 4775 file

Question 3

Which permission allows a user to run an executable file with the group permissions of the file, effectively giving them temporary access to the group that owns the file.

Answer 3

setgid permission on a file

Question 3

How can you identify the setgid permission on a file using ls -l?

Answer 3

→ The setgid permission is indicated by an “s” in the group’s execute position (e.g., -rwxr-sr-x).

Question 3

Which command allows you to setgid numerically?

Answer 3

add 2000 to the file’s existing permissions.

Question 3

What problem does the setgid permission solve in the scenario with users bob, sue, and tim working on a shared directory?

Answer 3

→ Without setgid, files created by one user are owned by their primary group, potentially preventing other users in the shared directory from accessing those files. Setgid ensures files are owned by the shared group.

Question 3

Which command allows you to setuid numerically?

Answer 3

add 4000 to the file’s existing permissions.

Question 3

Which permission prevents users from deleting files they do not own in a shared directory, allowing only the owner of the file or the root user to delete files?

Answer 3

The sticky bit permission.

Question 3

Which data structure contains file metadata like permissions, ownership, and timestamps (but not the file name)?

Answer 3

→ The inode table.

Question 3

What command can be used to view the inode number of a file?

Answer 3

→ ls -i <file></file>

Question 4

Define the concept described as “two file names pointing to the same inode number.”

Answer 4

→ Hard link.

Question 4

What makes two files hard-linked copies of each other?

Answer 4

→ They share the same inode number.

Question 4

What command is used to create a hard link?

Answer 4

→ ln target link_name

Question 4

What is the file type indicator for a symbolic link in ls -l output?

Answer 4

→ l (lowercase L) as the first character in the permissions string.

Question 4

What is the main identifier for a file in the filesystem?

Answer 4

→ The inode number, not the file name.

Question 4

What does the arrow (->) in symbolic link listings indicate?

Answer 4

→ The target file that the link points to.

Question 5

Which type of link is described as a file that points to another file by its path?

Answer 5

→ Symbolic link (soft link).

Question 5

What command and option are used to create a symbolic link?

Answer 5

→ ln -s target link_name

Question 5

What is the key difference between a hard link and a symbolic link?

Answer 5

→ A hard link points to an inode; a symbolic link points to a pathname.

Question 5

Why can't hard links be used across different file systems?

Answer 5

→ Because each file system has its own set of inodes.

Question 5

Which link type clearly displays its target path in ls -l output?

Answer 5

→ Symbolic link.

Question 5

Which type of link cannot point to a directory and Which type of link allows linking to directories?

Answer 5

→ Hard link cannot point to a directory and → Symbolic link allows linking to directories.

Question 6

How do you add the sticky but numerically?

Answer 6

By adding 1000 to current permissions

Question 7

Which character means both the stickybit and execute permissions are available and which one means the execute permission is not available?

Answer 7

t means the stickybit and execute permissions are available and T means the execute permission is not available?

Question 8

Which special permission prevents users from deleting files they do not own in a shared writable directory like /tmp?

Answer 8

The sticky bit permission, which ensures only the file's owner or root can delete files in a shared directory.

Question 9

Which command symbolically enables the sticky bit on a directory?

Answer 9

chmod o+t directory_name

Question 9

Which identifier is used by the system to reference a file, independent of its name?

Answer 9

The inode number, a unique ID associated with each file on a filesystem.

Question 10

What does the number between file permissions and owner in ls -li output represent?

Answer 10

The link count, indicating how many hard links exist to that inode.

Question 11

Which link type ensures that deleting one of several linked files won’t remove the data?

Answer 11

Hard links, because the file data remains accessible as long as at least one link remains.

Question 11

Which command can help you find all filenames with the same inode number as a given file?

Answer 11

find / -inum 2> /dev/null, useful for locating hard links.

Question 12

Which type of link fails entirely if the original file it points to is removed?

Answer 12

Symbolic links

Question 13

Which link type is visually obvious and clearly shows its target in ls -l output?

Answer 13

Symbolic links, due to the -> arrow and the l file type indicator.

Question 13

Which type of link can cross filesystem boundaries or link across partitions?

Answer 13

Symbolic links, since they point to a path and not an inode.

Question 14

Which link type fails with a "cross-device link" error when crossing filesystems?

Answer 14

Hard links, due to inode numbers being unique to each filesystem.

Question 15

Which type of link cannot be created for a directory due to OS restrictions?

Answer 15

Hard links, as linking to directories this way could compromise the filesystem hierarchy.

Question 16

Which link type is permitted for linking directories and often used in practice for organization?

Answer 16

Symbolic links, which can point to directories without issues.

Question 16

Which command creates a symbolic link named binary pointing to the /bin directory?

Answer 16

ln -s /bin binary, producing a visible soft link in the working directory.

Question 17

Which type of file acts as a shortcut that "points to" another file, allowing indirect access to its contents?

Answer 17

A symbolic link (also called a soft link), which stores a path to the target file and redirects operations to it.

Question 18

Which command creates a symbolic link named link_name that points to a target file?

Answer 18

ln -s target link_name

Question 19

What would the command ln -s /etc/passwd mypasswd create in the current directory?

Answer 19

A symbolic link named mypassword that points to the /etc/passwd file.

Question 20

Which file type allows two different filenames to reference the same inode, thereby making them equivalent in access and content?

Answer 20

A hard link, which points directly to the same inode as the original file.

Question 21

Which block of data in a file system stores metadata like permissions, ownership, and timestamps—but not filenames or file contents?

Answer 21

The inode table, which maps inodes to file data and attributes.

Question 22

Which command would you use to view both the inode and link count of files in long format?

Answer 22

ls -li, which shows inode, permissions, link count, and other metadata.

Question 23

Which command creates file.hard.1 as a hard link to file.original

Answer 23

ln file.original file.hard.1

Question 24

/tmp and /var/tmp are examples of which type of directories?

Answer 24

/tmp and /var/tmp are examples of sticky bit directories

Question 25

In which 2 directories are all users allowed to create temporary files?

Answer 25

/tmp and /var/temp

Question 26

Create a file named source containing the text "data"

Answer 26

echo "data" > source

Question 27

Which command is used to delete a file?

Answer 27

The rm command

Question 28

Which type of links do not increase the link count of files with which they are linked?

Answer 28

Symbolic links