Quiz: Root Access, Boot Process, File Systems, Partitions, and Mounting

1. True/False

The root user is the superuser account and has the highest access rights on a Linux system.

Answer: True

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2. True/False

It is recommended to stay logged in as root for normal daily work because it is faster.

Answer: False
Explanation: Staying logged in as root is risky because mistakes may affect the entire system.

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3. Multiple Choice

Which command is preferred when you need to run one privileged command?

A. su -
B. sudo command
C. exit
D. whoami

Answer: B. sudo command

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4. Multiple Choice

What does the command below do?

su -

A. Runs one command as root
B. Opens a login shell as root
C. Shows the current user
D. Lists mounted filesystems

Answer: B. Opens a login shell as root

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5. Multiple Choice

Which process is usually started by the kernel as the first userspace process?

A. GRUB
B. BIOS
C. systemd or init
D. fdisk

Answer: C. systemd or init

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6. Multiple Choice

Which systemd target usually represents a non-graphical multi-user system?

A. poweroff.target
B. rescue.target
C. multi-user.target
D. graphical.target

Answer: C. multi-user.target

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7. Multi-Select

Which of the following are risks of using the root account directly?

Select all that apply.

A. Accidental system-wide file changes
B. Running ordinary tasks with unnecessary privileges
C. Forgetting that you are logged in as root
D. More accountability than sudo
E. Background processes may run with root privilege

Answers: A, B, C, E

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8. Multi-Select

Which commands are commonly part of the basic partition, format, mount, and verify workflow?

Select all that apply.

A. lsblk
B. fdisk
C. mkfs
D. mount
E. df -h
F. passwd

Answers: A, B, C, D, E

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9. Multi-Select

Which statements about filesystems are correct?

Select all that apply.

A. A filesystem organizes data and metadata on storage
B. Journaling can reduce recovery time after an unclean shutdown
C. ext4 is commonly used on many Linux distributions
D. FAT is a modern Linux-native journaling filesystem
E. NTFS is associated with Microsoft Windows

Answers: A, B, C, E

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10. Fill in the Blank with Choices

A filesystem defines how __________ and metadata are organized and accessed on a storage device.

A. users
B. data
C. passwords
D. targets

Answer: B. data

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11. Fill in the Blank with Choices

The Linux filesystem table is stored in the file __________.

A. /etc/passwd
B. /etc/fstab
C. /boot/grub
D. /var/log

Answer: B. /etc/fstab

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12. Fill in the Blank with Choices

On modern systems, __________ is normally preferred over MBR for large disks unless compatibility requires MBR.

A. FAT
B. GPT
C. ext2
D. BIOS

Answer: B. GPT

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13. Matching

Match each FHS directory with its purpose.

Directory	Purpose
1. /etc	A. User home directories
2. /var	B. Device files
3. /home	C. System-wide configuration files
4. /dev	D. Logs and changing data
5. /boot	E. Boot loader files and kernels

Answer:

Directory	Correct Purpose
/etc	C
/var	D
/home	A
/dev	B
/boot	E

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14. Matching

Match each command with its purpose.

Command	Purpose
1. lsblk	A. Format a partition with a filesystem
2. fdisk	B. Show block devices
3. mkfs	C. Modify partition tables
4. mount	D. Attach a filesystem to the Linux directory tree
5. umount	E. Detach a mounted filesystem

Answer:

Command	Correct Purpose
lsblk	B
fdisk	C
mkfs	A
mount	D
umount	E

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15. Ordering

Put the boot stages in the correct order.

A. Kernel starts init/systemd
B. BIOS/UEFI starts
C. GRUB loads the selected kernel
D. System reaches target/services
E. MBR or boot loader code begins the boot manager stage

Correct Order:

1. B
2. E
3. C
4. A
5. D

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16. Ordering

Put the storage setup steps in the correct order.

A. Format the partition with mkfs
B. Identify the disk with lsblk
C. Mount the filesystem
D. Create a partition using fdisk
E. Verify using df -h

Correct Order:

1. B
2. D
3. A
4. C
5. E

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17. Short Answer

Explain the difference between sudo and su -.

Sample Answer:
sudo runs a single command with elevated privileges and logs the action. su - opens a new login shell as another user, usually root if no username is provided. sudo is safer for one administrative task, while su - is used when a full shell as another user is needed.

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18. Hands-on Short Answer

Write commands to format /dev/sdb1 as ext4, create /mnt/test, mount the partition, and verify it.

Sample Answer:

sudo mkfs -t ext4 /dev/sdb1
sudo mkdir -p /mnt/test
sudo mount -t ext4 /dev/sdb1 /mnt/test
df -h

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19. Analytical Short Answer

Why is /dev/sdb commonly used with fdisk, but /dev/sdb1 is commonly used with mkfs?

Sample Answer:
/dev/sdb represents the whole disk, so fdisk uses it to create or modify the disk’s partition table. /dev/sdb1 represents a specific partition, so mkfs formats that partition with a filesystem.

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20. Higher-Order Short Answer

A server should automatically mount a new ext4 partition after every reboot. Which file should be configured, and what information does it need?

Sample Answer:
The file /etc/fstab should be configured. It needs the filesystem or UUID, mount point, filesystem type, mount options, dump value, and filesystem check pass value. Example pattern:

UUID=... /mnt/data ext4 defaults 0 2

This allows the system to mount the filesystem automatically during boot.

REF: AI Tools/ChatGPT

Linux Special Permissions: SUID, SGID, and Sticky Bit

Linux normally uses three permission groups:

u = user/owner
g = group
o = others

And three basic permissions:

r = read
w = write
x = execute

Example:

ls -l file.txt

Output:

-rwxr-xr--

But Linux also has special permissions:

SUID       = user +s
SGID       = group +s
Sticky Bit = others +t

They appear in ls -l output as:

s, S, t, or T

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1. SUID — Set User ID

Meaning

SUID means:

When an executable file runs, it runs with the permission of the file owner, not the user who started it.

SUID is mainly useful on executable programs, not normal text files.

Set SUID

chmod u+s filename

Numeric form:

chmod 4755 filename

The 4 means SUID.

Remove SUID

chmod u-s filename

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Example: /usr/bin/passwd

The passwd command lets a normal user change their own password.

ls -l /usr/bin/passwd

Possible output:

-rwsr-xr-x 1 root root ... /usr/bin/passwd

Notice:

rws

The s appears in the user execute position.

Normal owner permission would be:

rwx

With SUID, it becomes:

rws

Because /usr/bin/passwd is owned by root, when a normal user runs:

passwd

the program temporarily runs with the file owner’s privilege, which is root, but only for the controlled task of changing the password.

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SUID: lowercase s vs uppercase S

This is very important.

Lowercase s

Lowercase s means:

SUID is set AND owner execute permission exists.

Example:

touch demo
chmod 755 demo
chmod u+s demo
ls -l demo

Output:

-rwsr-xr-x 1 user user ... demo

Here:

rws

means:

owner has read + write + execute
SUID is also set

Uppercase S

Uppercase S means:

SUID is set BUT owner execute permission is missing.

Example:

touch demo
chmod 644 demo
chmod u+s demo
ls -l demo

Output:

-rwSr--r-- 1 user user ... demo

Here:

rwS

means:

SUID is set
but owner execute permission is missing

So uppercase S usually means the special permission is set, but it is not useful for execution because x is missing.

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2. SGID — Set Group ID

Meaning on files

SGID on an executable file means:

When the file runs, it runs with the permission of the file’s group owner.

Meaning on directories

SGID is especially useful on directories.

On a directory, SGID means:

New files and subdirectories created inside the directory inherit the directory’s group ownership.

This is very useful for shared project folders.

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Set SGID

chmod g+s filename_or_directory

Numeric form:

chmod 2755 filename_or_directory

The 2 means SGID.

Remove SGID

chmod g-s filename_or_directory

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Example: Shared project directory

Suppose we have a group named developers.

sudo mkdir /project
sudo chgrp developers /project
sudo chmod 2775 /project

Check:

ls -ld /project

Possible output:

drwxrwsr-x 2 root developers ... /project

Notice the group part:

rws

That means:

group has read + write + execute
SGID is set

Now when a user creates a file inside /project, the file can inherit the directory’s group:

touch /project/app.txt
ls -l /project/app.txt

Possible output:

-rw-r--r-- 1 alice developers ... app.txt

Even if Alice’s normal primary group is different, the file is created with the developers group because the parent directory has SGID.

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SGID: lowercase s vs uppercase S

Lowercase s

Lowercase s means:

SGID is set AND group execute permission exists.

Example:

mkdir shared
chmod 775 shared
chmod g+s shared
ls -ld shared

Output:

drwxrwsr-x 2 user user ... shared

The group permission part is:

rws

This means SGID is set and the group can enter/search the directory.

Uppercase S

Uppercase S means:

SGID is set BUT group execute permission is missing.

Example:

mkdir shared
chmod 764 shared
chmod g+s shared
ls -ld shared

Output:

drwxrwSr-- 2 user user ... shared

The group permission part is:

rwS

This means SGID is set, but group execute is missing.

For a directory, this is usually a problem because group members need x permission to enter or access items inside the directory.

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3. Sticky Bit

Meaning

The Sticky Bit is mostly used on directories.

It means:

Users can create files in the directory, but they can delete only their own files.

This is useful for shared writable directories.

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Set Sticky Bit

chmod o+t directory

Numeric form:

chmod 1777 directory

The 1 means Sticky Bit.

Remove Sticky Bit

chmod o-t directory

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Example: /tmp

The /tmp directory is shared by many users and programs.

ls -ld /tmp

Possible output:

drwxrwxrwt 10 root root ... /tmp

Notice the last character:

t

That means Sticky Bit is set.

The directory is writable by many users, but one user cannot delete another user’s files.

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Example: Create a shared temporary directory

sudo mkdir /sharedtmp
sudo chmod 1777 /sharedtmp
ls -ld /sharedtmp

Output:

drwxrwxrwt 2 root root ... /sharedtmp

Now different users can create files inside /sharedtmp, but they cannot delete files owned by other users.

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Sticky Bit: lowercase t vs uppercase T

Sticky Bit uses t or T, not s or S.

Lowercase t

Lowercase t means:

Sticky Bit is set AND others execute permission exists.

Example:

mkdir sharedtmp
chmod 777 sharedtmp
chmod o+t sharedtmp
ls -ld sharedtmp

Output:

drwxrwxrwt 2 user user ... sharedtmp

The others permission part is:

rwt

This means:

others have read + write + execute
Sticky Bit is set

Uppercase T

Uppercase T means:

Sticky Bit is set BUT others execute permission is missing.

Example:

mkdir sharedtmp
chmod 776 sharedtmp
chmod o+t sharedtmp
ls -ld sharedtmp

Output:

drwxrwxrwT 2 user user ... sharedtmp

The others permission part is:

rwT

This means Sticky Bit is set, but others do not have execute permission.

For a directory, this usually means others cannot properly enter or access the directory.

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Quick Summary of s, S, t, and T

Symbol	Location in ls -l	Meaning
s	user execute position	SUID set and user execute exists
S	user execute position	SUID set but user execute missing
s	group execute position	SGID set and group execute exists
S	group execute position	SGID set but group execute missing
t	others execute position	Sticky Bit set and others execute exists
T	others execute position	Sticky Bit set but others execute missing

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Visual Examples

Normal executable file

-rwxr-xr-x

Owner has execute permission.

SUID with execute

-rwsr-xr-x

SUID is active and owner execute exists.

SUID without execute

-rwSr-xr-x

SUID is set, but owner execute is missing.

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Normal group-executable directory

drwxrwxr-x

Group has execute permission.

SGID directory with execute

drwxrwsr-x

SGID is active and group execute exists.

SGID directory without group execute

drwxrwSr-x

SGID is set, but group execute is missing.

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Sticky Bit directory with others execute

drwxrwxrwt

Sticky Bit is active and others execute exists.

Sticky Bit directory without others execute

drwxrwxrwT

Sticky Bit is set, but others execute is missing.

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Numeric Permission Summary

Special permissions are added before the normal three permission digits.

Permission	Numeric value	Example
SUID	4	chmod 4755 program
SGID	2	chmod 2775 shareddir
Sticky Bit	1	chmod 1777 sharedtmp

Examples:

chmod 4755 program      # SUID + rwxr-xr-x
chmod 2755 directory    # SGID + rwxr-xr-x
chmod 1777 directory    # Sticky Bit + rwxrwxrwx

You can also combine them:

chmod 6755 program

Here:

6 = 4 + 2

So 6755 means:

SUID + SGID + rwxr-xr-x

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Command Summary

Set SUID:

chmod u+s program

Remove SUID:

chmod u-s program

Set SGID:

chmod g+s directory

Remove SGID:

chmod g-s directory

Set Sticky Bit:

chmod o+t directory

Remove Sticky Bit:

chmod o-t directory

Check permissions:

ls -l filename
ls -ld directory

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Practical Use Cases

SUID use case

Used when a normal user needs to run a specific program with the file owner’s privileges.

Common example:

ls -l /usr/bin/passwd

Possible output:

-rwsr-xr-x 1 root root ... /usr/bin/passwd

This allows users to change their passwords safely without giving them full root access.

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SGID use case

Used for shared team directories.

Example:

sudo mkdir /team
sudo chgrp developers /team
sudo chmod 2775 /team

Result:

drwxrwsr-x root developers /team

Files created inside /team inherit the developers group.

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Sticky Bit use case

Used for shared writable directories where users should not delete each other’s files.

Example:

sudo mkdir /publicdrop
sudo chmod 1777 /publicdrop

Result:

drwxrwxrwt root root /publicdrop

Users can create files, but they cannot delete other users’ files.

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Final Blog Summary

SUID: Run an executable as the file owner.
SGID: Run an executable as the file group, or make files inherit a directory group.
Sticky Bit: In shared directories, users can delete only their own files.

The lowercase letters mean the related execute permission is present:

s = SUID/SGID + execute
t = Sticky Bit + execute

The uppercase letters mean the special permission is set, but execute is missing:

S = SUID/SGID set, execute missing
T = Sticky Bit set, execute missing

For practical use, lowercase s and t are usually what you expect to see. Uppercase S or T often indicates a permission setup that should be reviewed.

REF: AI Tools/ChatGPT