Sysadmin cheat sheet¶

Exercise sysadmin-cheat-sheet-annex.pdf · PDF

A pilot with 10,000 hours of flight still reads a checklist before take-off. Not because she forgot how to fly: because memory fails under pressure.

A system administrator works the same way. At 3 a.m., with a service down and a boss on the phone, nobody remembers whether it was usermod -G or usermod -aG — and the wrong one does damage. Since February you have met dozens of commands: users, passwords, permissions, processes, services, logs, monitoring, configuration. Today you put the ones you forget on one page, in your own handwriting, and you find out what you really know.

What a good cheat sheet looks like¶

A cheat sheet is a one-page summary of the commands you need, organised so you can find the right one in seconds.

Which of these two helps you at 3 a.m.?

usermod   modify a user account
chage     change user password expiry information

Add joan to the group design (keep his groups)   sudo usermod -aG design joan
Make pau change his password at next login       sudo chage -d 0 pau

The first one is a dictionary: you must already know the word to look it up. The second one starts from what you want to do. That gives three rules:

Use the names of Tramuntana Apps — marta, joan, aina, pau, the groups dev, design, admin, the folder /srv/tramuntana — so every line is something you could type tomorrow.

Memory first, then check, then test¶

The Exercise sheet has eight boxes, A to H, one per topic of the unit. You fill them in three steps:

flowchart LR
    S1["<b>1 · From memory</b><br>notes closed, pen<br>leave gaps where you forget"] --> S2["<b>2 · Check</b><br>notes, man, --help, deb-lab<br>fill gaps in another colour"]
    S2 --> S3["<b>3 · Test</b><br>a neighbour runs one of<br>your lines exactly as written"]
    S3 -->|"it fails"| FIX["<b>Fix the line</b>"]

• Step 1 — from memory. Notes closed, VM untouched. Write the tasks and commands you remember. Where you remember the task but not the command, write the task and leave a gap.
• Step 2 — check. Now open the notes, man, --help and deb-lab. Fill the gaps and correct mistakes in another colour. That second colour is the map of what you must study.
• Step 3 — test. Swap sheets. Your neighbour picks one line and runs it in deb-lab exactly as you wrote it. If it fails, you fix it.

What the boxes can hold¶

After step 1, compare your sheet with this list. It is not a sheet to copy: it shows the kind of line worth having. Keep only the ones you forget, and the pages of this unit explain each of them.

The traps that cost the most points¶

Two lines lose more points than any other, every year. Put them on your sheet with a warning.

In short: enable = at boot, start = now, enable --now = both.

The retrieval quiz¶

The back of the Exercise sheet is a quiz of twelve tasks: cheat sheet face down, eight minutes, then you swap and correct. The mark does not count; what counts is the list of questions you missed. Here is the kind of task it asks, with an answer that works (any equivalent command is right):

Before you leave, mark the box of your sheet with the most gaps after step 1. That is what you revise first.

Key takeaways¶

• A good cheat sheet goes task first, command second, with a real example, and holds only what you forget.
• Build it in three steps: from memory, then check in another colour, then test a line on a real machine.
• Retrieval practice — trying to remember before looking — is what makes commands stick; recognising a command is not recalling it.
• The second colour on your sheet is the map of what to study before the exam.
• The two classic traps: usermod -G without -a drops the user's other groups; enable without --now does not start the service now.

Quick check¶

Next: fill box G — Maintenance and optimisation.