Lab 10: App Admin

Published

2026-08-05

WarningCaution

This section is being revised. Thank you for your patience.

Comprehension questions

“What are two different ways to install Linux applications, and what are the commands?”

My instance is Amazon Linux 2, so the system package manager is yum, not Ubuntu’s apt:

  • sudo yum install <package> pulls a package (and its dependencies) from AL2’s configured repositories.
    • sudo yum update keeps everything already installed current.
  • For software that isn’t in the repos, I download the package myself with wget <url> and install it directly: sudo yum localinstall <package>.rpm (or sudo rpm -i <package>.rpm).
    • No dependency resolution beyond what’s already on the box, so this is my second choice, not my first.

“What does it mean to daemonize a Linux application? What programs and commands are used to do so?”

Daemonizing an application means running it as a background service that starts on boot, restarts if it crashes, and keeps running independent of any login session - instead of a process that dies the moment I close my SSH connection.

On AL2, systemd is the program that manages this, and systemctl is how I talk to it:

%%{init: {'theme': 'base', 'themeVariables': {'fontFamily': 'monospace', "fontSize":"12px"}}}}%%

graph TD
    subgraph Unit["Unit File"]
        DotService["<strong>/etc/systemd/system/*.service</strong>"]
    end
    Reload["<strong>systemctl daemon-reload</strong>"]
    Enable["<strong>systemctl enable</strong>"]
    Start["<strong>systemctl start</strong>"]
    Status["<strong>systemctl status</strong>"]

    Unit --> Reload --> Enable --"<em>starts on boot</em>"--> Start --"<em>running now</em>"--> Status

    style DotService stroke:#fff,stroke-width:1px,color:#000,font-family:monospace
    style Unit fill:#1B2A41,stroke:#fff,stroke-width:1px,color:#fff,font-family:monospace
    style Reload fill:#2A6F77,stroke:#fff,stroke-width:1px,color:#fff,font-family:monospace
    style Enable fill:#2A6F77,stroke:#fff,stroke-width:1px,color:#fff,font-family:monospace
    style Start fill:#5B8C5A,stroke:#fff,stroke-width:1px,color:#fff,font-family:monospace
    style Status fill:#E8A33D,stroke:#000,stroke-width:1px,color:#000,font-family:monospace

Daemonizing with systemd

Once the unit file exists, systemctl restart and systemctl stop manage it going forward, and systemctl disable stops it from starting on boot.

“How do you know if you’ve opened Nano or Vim? How would you exit them if you didn’t mean to?”

Nano tells me right away - the bottom of the screen fills with a menu of keybindings (^X Exit, ^O Write Out, etc.), and I can just start typing. Vim gives no such hints: it opens in normal mode, the screen is otherwise blank (empty lines marked with ~), and typing does nothing useful until I switch to insert mode. That silence is usually how I know I’ve landed in Vim by accident.

To back out without changing anything:

Nano: Ctrl + X, then answer N if it asks whether to save

Vim: press Esc first to make sure I’m in normal mode (not typing into the file), then type :q! and hit Enter to quit and discard any changes.

“What are four commands to read text files?”

cat, less, head, and tail. I reach for cat on short files, less for anything long enough to scroll, head when I only need the first lines, and tail -f when I want to watch a log file update in real time.

“How would you create a file called secrets.txt, open it with Vim, write something in, close and save it, and make it so that only you can read it?”

vim secrets.txt

From there:

  1. Press i to enter insert mode and type the content.
  2. Press Esc to return to normal mode.
  3. Type :wq and hit Enter to write (save) and quit.

Then lock it down so only I can read it:

chmod 600 secrets.txt

600 gives the owner read/write and removes every permission for group and other - same restriction I already use on .ssh/authorized_keys in Linux Users.