Quiz — Linux Fundamentals

Quiz Overview

Validate core Linux administration skills used daily by DevOps and SRE engineers: filesystem layout, permissions, processes, systemd, logging, and incident judgement.

Attribute	Value
Topic	Linux
Questions	40
Passing score	70% (28 correct)
Estimated time	45–60 minutes
Format	Multiple choice (single answer)

How to use this quiz

Attempt each section without peeking. Use Reveal answer only after you commit to a choice. Score yourself honestly — gaps are the point.

Rewritten course quiz

For the Linux for Cloud & DevOps Engineers 16-module track, prefer Linux for Cloud & DevOps Fundamentals.

Learning Objectives

This quiz assesses whether you can:

• Explain kernel vs user space and FHS basics
• Apply permissions, ownership, and sudo safely
• Operate systemd units and journald
• Triage failed services, disk pressure, and port conflicts
• Choose hardening and backup patterns that match production norms

Section 1 — Fundamentals

Question 1

What is the primary role of the Linux kernel?

Difficulty: Beginner

Options:

• A. Manage hardware, processes, memory, and system calls for user space
• B. Provide a graphical desktop environment
• C. Replace Bash as the default shell
• D. Store user documents in /home only

Reveal answer

Correct answer: A

The kernel is the core of the OS: hardware abstraction, scheduling, memory, and the system-call interface. Desktops and shells are user-space components.

Related concepts

• Kernel vs user space
• System calls
• Process scheduling

Question 2

Which path is the conventional location for third-party or locally installed software trees on many Linux systems?

Difficulty: Beginner

Options:

• A. /var/log
• B. /proc
• C. /opt
• D. /dev

Reveal answer

Correct answer: C

/opt is commonly used for optional/add-on application packages. /var/log is logs, /proc is process/kernel info, /dev is device nodes.

Related concepts

• FHS
• /opt
• Filesystem hierarchy

Question 3

What does the execute bit on a directory allow a user to do?

Difficulty: Beginner

Options:

• A. List all filenames without reading them
• B. Delete the directory itself without write on the parent
• C. Change ownership of every file inside
• D. Traverse into the directory (access files by known name if other permissions allow)

Reveal answer

Correct answer: D

On directories, execute means search/traverse. Listing needs read; creating/deleting entries needs write on the directory.

Related concepts

• Directory permissions
• rwx on directories

Question 4

Which command shows your effective user id, groups, and supplementary groups?

Difficulty: Beginner

Options:

• A. whoami only
• B. id
• C. uname -a
• D. pwd

Reveal answer

Correct answer: B

id prints uid, gid, and groups. whoami is only the username; uname is kernel/system identity.

Related concepts

• Users and groups
• id

Question 5

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

Difficulty: Beginner

Options:

• A. A hard link is another directory entry to the same inode; a symlink is a special file pointing to a path
• B. Hard links can cross filesystems; symlinks cannot
• C. Symlinks only work for directories; hard links only for devices
• D. They are identical on ext4

Reveal answer

Correct answer: A

Hard links share an inode (same filesystem). Symlinks store a path and can cross filesystems.

Related concepts

• Inodes
• ln
• ln -s

Question 6

Which signal is the default sent by kill <pid> when no signal is specified?

Difficulty: Beginner

Options:

• A. SIGKILL (9)
• B. SIGSTOP
• C. SIGTERM (15)
• D. SIGHUP

Reveal answer

Correct answer: C

Default is SIGTERM, allowing graceful shutdown. SIGKILL cannot be caught and should be a last resort.

Related concepts

• Signals
• kill

Question 7

What does systemd use as the primary unit type for long-running daemons?

Difficulty: Beginner

Options:

• A. .timer units only
• B. .mount units exclusively
• C. .socket units replace all services
• D. .service units

Reveal answer

Correct answer: D

Daemons are typically managed as .service units. Timers, mounts, and sockets are other unit types.

Related concepts

• systemd
• Unit files

Question 8

Which command is the modern preferred way to follow logs for a systemd service named nginx?

Difficulty: Beginner

Options:

• A. tail -f /var/log/messages only
• B. journalctl -u nginx -f
• C. dmesg -w
• D. cat /proc/nginx

Reveal answer

Correct answer: B

journalctl -u <unit> -f follows that unit’s journal entries.

Related concepts

• journalctl
• Logging

Question 9

In a classic Unix permission string -rwxr-xr--, what can “others” do?

Difficulty: Beginner

Options:

• A. Read only
• B. Read, write, and execute
• C. Read and execute
• D. Nothing

Reveal answer

Correct answer: A

The last triad is r-- → others may read only.

Related concepts

• chmod
• Permission triads

Question 10

What is the purpose of /etc/sudoers (or files under /etc/sudoers.d)?

Difficulty: Beginner

Options:

• A. Store user passwords in plaintext
• B. Configure SSH host keys
• C. Define which users/groups may run commands as root or others via sudo
• D. Set the default shell for root only

Reveal answer

Correct answer: C

sudoers controls privilege elevation policy. Edit with visudo to avoid syntax lockouts.

Related concepts

• sudo
• Least privilege
• visudo

Section 2 — Practical Knowledge

Question 11

You need to find all world-writable files under /var/www for a hardening review. Which approach is most appropriate?

Difficulty: Intermediate

Options:

• A. ls -la /var/www
• B. chmod -R 777 /var/www
• C. cat /etc/passwd
• D. find /var/www -type f -perm -0002

Reveal answer

Correct answer: D

find … -perm -0002 locates files with the others-write bit.

Related concepts

• find
• Permissions audit

Question 12

A service fails immediately after systemctl start. What should you run first for evidence?

Difficulty: Intermediate

Options:

• A. reboot
• B. systemctl status and journalctl -u -e
• C. rm -rf /etc/systemd
• D. kill -9 1

Reveal answer

Correct answer: B

Status and journal give exit codes, paths, and permission errors.

Related concepts

• Incident triage
• journalctl
• systemctl

Question 13

Which chmod symbolic mode adds execute for user and group on deploy.sh?

Difficulty: Intermediate

Options:

• A. chmod ug+x deploy.sh
• B. chmod a+s deploy.sh
• C. chmod o+w deploy.sh
• D. chmod 000 deploy.sh

Reveal answer

Correct answer: A

ug+x adds execute for user and group without forcing a full octal mode.

Related concepts

• chmod symbolic mode

Question 14

Which command helps identify large directories under /var?

Difficulty: Intermediate

Options:

• A. ps aux
• B. ip addr
• C. du -h --max-depth=1 /var | sort -h
• D. systemctl list-timers

Reveal answer

Correct answer: C

du summarises disk usage by directory.

Related concepts

• du
• Disk pressure

Question 15

What does systemctl enable nginx do?

Difficulty: Intermediate

Options:

• A. Starts nginx once and disables it on reboot
• B. Upgrades the nginx package
• C. Opens port 80 in the firewall
• D. Creates the wants/ symlinks so nginx starts on boot (per unit install section)

Reveal answer

Correct answer: D

enable configures boot-time start via unit WantedBy relationships.

Related concepts

• systemctl enable

Question 16

Which crontab field set runs a job at 02:30 every day?

Difficulty: Intermediate

Options:

• A. 2 30 * * *
• B. 30 2 * * *
• C. * * 2 30 *
• D. 30 * 2 * *

Reveal answer

Correct answer: B

Order is minute hour day-of-month month day-of-week → 30 2 * * *.

Related concepts

• cron

Question 17

You need lines containing ERROR in app.log, case-insensitive. Best simple command?

Difficulty: Beginner

Options:

• A. grep -i ERROR app.log
• B. rm app.log
• C. chmod 777 app.log
• D. ln -s app.log

Reveal answer

Correct answer: A

grep -i matches case-insensitively.

Related concepts

• grep
• Log analysis

Question 18

What is a reliable way to see which process holds TCP port 8080?

Difficulty: Intermediate

Options:

• A. cat /etc/services only
• B. echo 8080
• C. ss -ltnp | grep 8080 (or lsof -iTCP:8080)
• D. uname -r

Reveal answer

Correct answer: C

ss/lsof show listeners and owning processes.

Related concepts

• ss
• lsof

Question 19

A script must fail fast if any command fails. Which Bash option helps?

Difficulty: Intermediate

Options:

• A. set +x only
• B. alias rm=rm
• C. ulimit -n 1
• D. set -e (and often set -u -o pipefail)

Reveal answer

Correct answer: D

set -e exits on failure; combining with -u and pipefail is common.

Related concepts

• Bash
• set -e

Question 20

Which permission bit on a directory makes files deletable only by their owner (or root) — classic /tmp behaviour?

Difficulty: Intermediate

Options:

• A. setuid
• B. sticky bit (t)
• C. setgid
• D. immutable attribute only

Reveal answer

Correct answer: B

The sticky bit on directories restricts unlinking to file owner/root.

Related concepts

• Sticky bit
• /tmp

Section 3 — Scenario-Based Questions

Question 21

PagerDuty: rebash-api failed. journalctl reports Permission denied opening the ExecStart script. Best next step?

Difficulty: Intermediate

Options:

• A. Check ownership/mode of the script and the user the unit runs as (User=)
• B. Open all firewall ports
• C. Delete the unit file
• D. Disable SELinux permanently without investigation

Reveal answer

Correct answer: A

Permission denied on the executable path implicates ownership/mode vs the service user.

Related concepts

• systemd User=
• Permissions

Question 22

Disk is 100% on /. du shows /var/log huge. Safest immediate mitigation while preserving evidence?

Difficulty: Intermediate

Options:

• A. rm -rf /
• B. dd if=/dev/zero of=/var/log/big
• C. Rotate/compress old logs, truncate only after copying critical evidence, fix retention
• D. chmod -R 777 /var/log

Reveal answer

Correct answer: C

Free space via log rotation/cleanup with care for forensics.

Related concepts

• Disk full
• logrotate

Question 23

A timer-based job did not run. systemctl list-timers shows the timer inactive. Likely check?

Difficulty: Intermediate

Options:

• A. Whether Docker is installed
• B. Whether /etc/hosts contains google.com
• C. Whether the GPU driver exists
• D. Whether the .timer unit is enabled/started and OnCalendar= is valid

Reveal answer

Correct answer: D

Timers must be enabled/started; calendar expressions and related service units matter.

Related concepts

• systemd timers

Question 24

SSH works from your laptop but CI fails with Permission denied (publickey). Most likely?

Difficulty: Intermediate

Options:

• A. The server has no SSH daemon
• B. The runner lacks the authorised private key or uses the wrong user
• C. iptables blocks ICMP only
• D. DNS TTL is 86400

Reveal answer

Correct answer: B

Publickey failures usually mean missing/incorrect key material or wrong account.

Related concepts

• SSH keys
• CI authentication

Question 25

htop shows one process at 100% CPU after a release. Sound first step?

Difficulty: Intermediate

Options:

• A. Identify PID, inspect command line/logs, thread state; consider SIGTERM after evidence
• B. kill -9 -1
• C. Disable the NIC
• D. Format /home

Reveal answer

Correct answer: A

Diagnose before killing broadly.

Related concepts

• CPU saturation
• Process triage

Question 26

A junior proposes chmod -R 777 /var/www to fix the site. What do you recommend?

Difficulty: Beginner

Options:

• A. Agree — 777 is fine in production
• B. World-writable is required for nginx
• C. Set owner/group correctly and use the least mode that works (often 755 dirs / 644 files)
• D. Put the site in /proc

Reveal answer

Correct answer: C

777 is a common anti-pattern. Fix ownership and minimal modes.

Related concepts

• Least privilege

Question 27

You need elevation but policy forbids sharing the root password. Appropriate tool?

Difficulty: Beginner

Options:

• A. Write the root password to Slack
• B. Disable PAM
• C. chmod 777 /etc/shadow
• D. sudo -i (if authorised) or sudo for specific commands

Reveal answer

Correct answer: D

sudo provides audited, policy-controlled elevation.

Related concepts

• sudo
• Access control

Question 28

Application writes to /var/lib/myapp but the unit uses ProtectSystem=strict. What happens?

Difficulty: Advanced

Options:

• A. Nothing — ProtectSystem is cosmetic
• B. Writes outside allowed paths fail; use ReadWritePaths= (or relax carefully)
• C. The kernel panics
• D. SELinux is disabled

Reveal answer

Correct answer: B

systemd sandboxing restricts filesystem writes.

Related concepts

• systemd hardening
• ProtectSystem

Question 29

SSH latency is fine but authentication takes ~10s. A common cause?

Difficulty: Advanced

Options:

• A. Reverse DNS / GSSAPI / UseDNS delays in sshd
• B. MTU 9000 only
• C. Missing /etc/hostname always blocks forever
• D. Too much free RAM

Reveal answer

Correct answer: A

SSH can stall on reverse DNS or auth method negotiation.

Related concepts

• sshd
• UseDNS

Question 30

Prove a package is installed and which version on Debian/Ubuntu. Best pair?

Difficulty: Intermediate

Options:

• A. brew list
• B. systemctl reboot
• C. dpkg -l | grep pkg ; apt-cache policy pkg
• D. tar -tzf

Reveal answer

Correct answer: C

dpkg/apt query package state on Debian family systems.

Related concepts

• Package management
• dpkg

Section 4 — Troubleshooting

Question 31

Unit is active (running) but curl fails; ss shows nothing listening. Likely category?

Difficulty: Intermediate

Options:

• A. The moon phase
• B. ext4 fragmentation only
• C. Missing swap always
• D. Process is up but bound to a different address/port or crashed child listener

Reveal answer

Correct answer: D

A parent can be running while the listener failed or binds elsewhere.

Related concepts

• Listen address
• Health checks vs process state

Question 32

journalctl -u app shows ExecStart path not found. Fix?

Difficulty: Beginner

Options:

• A. chmod 777 /
• B. Correct the path in the unit, daemon-reload, restart
• C. Delete journald
• D. Disable the unit forever without fixing

Reveal answer

Correct answer: B

Broken ExecStart paths are fixed in the unit file followed by reload/restart.

Related concepts

• Unit files
• daemon-reload

Question 33

After apt upgrade, a service will not start due to a missing shared library. What helps confirm?

Difficulty: Advanced

Options:

• A. ldd on the binary / checking package dependencies
• B. ping 8.8.8.8 only
• C. changing wallpaper
• D. increasing nice value randomly

Reveal answer

Correct answer: A

ldd and dependency packages reveal missing libs after upgrades.

Related concepts

• Shared libraries
• ldd

Question 34

df -h shows space free but touch fails with “No space left”. Likely?

Difficulty: Advanced

Options:

• A. DNS failure
• B. Wrong timezone
• C. Inode exhaustion (df -i)
• D. Caps Lock

Reveal answer

Correct answer: C

Exhausted inodes can block new files while byte space remains.

Related concepts

• Inodes
• df -i

Question 35

A privileged port bind fails for a non-root service. Modern approach besides running as root?

Difficulty: Advanced

Options:

• A. Always chmod 777 the binary
• B. Disable the firewall globally
• C. Bind to port 22
• D. Use capabilities (e.g. CAP_NET_BIND_SERVICE), authbind, or reverse proxy on 80/443

Reveal answer

Correct answer: D

Prefer capabilities or a front proxy over running full root.

Related concepts

• Capabilities
• Privilege separation

Section 5 — Architecture

Question 36

For a single Linux VM hosting a public HTTPS API, which layering is most sound?

Difficulty: Intermediate

Options:

• A. App as root on :443 with 777 configs
• B. TLS terminator/reverse proxy + unprivileged app on localhost + firewall allow 80/443 only
• C. Disable SSH and hope
• D. Store secrets in a world-readable gist

Reveal answer

Correct answer: B

Terminate TLS at a hardened edge, run the app with least privilege, restrict exposure.

Related concepts

• Defence in depth
• Reverse proxy

Question 37

Why separate /var (or a dedicated log volume) on production servers?

Difficulty: Intermediate

Options:

• A. Contain log growth so a runaway log cannot fill the root filesystem as easily
• B. Aesthetic reasons only
• C. Makes kernel upgrades impossible
• D. Required by PCI to use XFS only

Reveal answer

Correct answer: A

Filesystem separation limits blast radius of growth and simplifies backups.

Related concepts

• Filesystem layout
• Capacity isolation

Question 38

Which backup statement is most accurate for Linux system state?

Difficulty: Intermediate

Options:

• A. RAID is a backup
• B. Snapshots without restore tests are enough forever
• C. Backups need retention, restore tests, and off-box copies — RAID is availability not backup
• D. Only back up /tmp

Reveal answer

Correct answer: C

RAID/redundancy is not a backup. Test restores.

Related concepts

• Backup
• Disaster recovery

Question 39

For SSH administration at scale, which design is preferable?

Difficulty: Advanced

Options:

• A. Shared root password on a wiki
• B. Telnet with OTP sticky notes
• C. FTP to edit /etc
• D. Per-user keys or SSO/cert auth, sudo for elevation, bastion/session recording as needed

Reveal answer

Correct answer: D

Key/cert auth, individual accounts, and audited sudo are baseline.

Related concepts

• SSH hardening
• Bastion

Question 40

A cost-conscious team runs batch jobs nightly on systemd hosts. Best approach?

Difficulty: Intermediate

Options:

• A. Busy-loop in a screen session
• B. systemd .timer + .service with clear logs and failure alerts
• C. Manual login each night
• D. Disable NTP so cron drifts

Reveal answer

Correct answer: B

Timers integrate with journald and dependency management.

Related concepts

• Timers
• Batch jobs

Score Summary

Score	Band	Meaning
36–40	Excellent	Ready for interviews and labs at this track level
28–35	Good	Pass — revise weak sections, then retry
20–27	Needs improvement	Revisit tutorials for missed topics before labs
≤19	Restart foundations	Work the track in order, then retake

Total questions: 40 · Passing score: 28 (70%)

Recommended Study Areas

Misses in Sections 1–2 → revisit early Linux tutorials. Misses in 3–4 → practise the Linux production incident lab. Misses in 5 → re-read security hardening and troubleshooting tutorials.

• Track: Linux
• Lab: Linux Production Incident Triage
• Cheat sheet: Linux
• Interview prep: Linux
• Path: DevOps Engineer

Interview Connection

Interviewers often ask permission bits on directories, systemd failure triage, journalctl workflows, and “disk full but df looks fine” (inodes). Be ready to narrate a service-down incident end-to-end.

References

1. systemd documentation
2. Linux man-pages project
3. Filesystem Hierarchy Standard