// Foundations

Explore Linux Fundamentals

Permissions make sense once you stop thinking in usernames and start thinking in UIDs.

Most Linux courses hand you `chmod` flags and a cheat sheet and hope the pattern sticks. Nugget starts one layer down: who the kernel actually checks (UIDs, not names), how that identity rides along on every process, and only then what the rwx triplet is deciding. Once that order is in your head, a permission string like `rwsr-xr-x` stops being trivia and starts being a story about what a binary can do and as whom.

You'll work through the parts that actually cause incidents — the difference between `usermod -G` and `-aG` (one quietly wipes your group memberships), why a sudoers line restricted to one command can still be a root shell away via GTFOBins, and why `kill -9` isn't the responsible default it feels like. Nugget draws the process states, the permission-check order, the PAM stack, and asks you to reason across them instead of just naming them back.

This runs alongside whatever OS or security course you're taking — it's the place to actually run the commands and get pushed on the parts your textbook glosses over, like why a D-state process laughs at every signal you throw at it.

// What a session feels like

You bring the questions. Nugget asks the next one.

You're staring at `ls -l /usr/bin/passwd` in the terminal and Nugget asks why that `s` in the execute field matters more than the rest of the permission string — you have to work out what runs as root and why that's necessary, not alarming.
Nugget sketches the four PAM management groups on the whiteboard and has you trace what happens when an `auth` line is marked `requisite` instead of `required` — you find the timing side-channel yourself before it explains why it matters.
In the Docker Linux lab, a process you spawned won't die under `kill -9`. Nugget has you check its state in `/proc/<PID>/status` and walks you toward the actual cause instead of letting you keep escalating signals that can't work.

// Pairs well with

GREP & Pattern Matching Networking Basics Python for Security

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