3.7. Reflection Checkpoint

Before moving to Phase 4, confirm you can answer these from understanding:

Files and Accounts:

• What is the practical difference between a hard link and a symbolic link? When can't you use a hard link?
• A file was deleted but the disk is still full. How do you identify and resolve this?
• What does usermod -G wheel alice do differently from usermod -aG wheel alice? Which is dangerous and why?
• What shell should a system service account use, and why?

Processes and Scheduling:

• A process is in D state. Can you kill it with kill -9? Why or why not?
• What is the difference between a zombie process and an orphan process?
• You start a command over SSH that needs to survive session disconnect. What two things must your command include?
• In cron format, what does */15 * * * * mean?

systemd and Packages:

• What is the difference between systemctl enable, systemctl start, and systemctl enable --now?
• After editing a unit file in /etc/systemd/system/, what command must you run before systemctl restart?
• What is systemctl mask and when would you use it instead of systemctl disable?
• dpkg -i package.deb fails with unmet dependencies. What apt command fixes this?

Containers:

• What is the key architectural difference between Docker and Podman?
• What is the difference between ENTRYPOINT and CMD in a Dockerfile?
• Port mapping -p 8080:80 — which is the host port and which is the container port?
• What volume flag is needed on RHEL/SELinux systems to allow container access to a bind-mounted host directory?