Packages, Storage & Filesystems

What is it?

A package manager (apt, dnf) installs, updates and removes software with dependencies. Storage is disks partitioned into filesystems mounted at paths; df shows usage, mount shows what is mounted where.

Why it matters

Software and disks are the two most common operational failures: an unpatched package is a vulnerability, and a full disk stops services and logging silently.

Where you see it

`apt update && apt upgrade` patches; `df -h` shows free space; `du -sh *` finds what is large; `/etc/fstab` defines mounts at boot.

What normal looks like

Packages current, disks well under full, mounts matching fstab, /var/log rotating so it never fills the disk.

What suspicious looks like

A disk at 100% (df shows 100% on /var), an outdated package with a known CVE, or a mount missing after reboot because fstab is wrong.

How analysts investigate

For 'out of space' run df -h then du to find the culprit; for software issues check installed version vs available; for a missing mount check fstab and dmesg.

Common beginner mistakes

Deleting files blindly to free space instead of finding the large offender with du.
Editing fstab wrong so the box won't boot — always keep a known-good copy.

Keep it patched and keep it free

  df -h
    /dev/sda1  20G  20G  0  100%  /var   ← FULL: services fail, logs stop
  du -sh /var/log/*  | sort -h
    9.8G  /var/log/app/verbose.log        ← the culprit
  → rotate/compress the log + fix the app, don't blind-delete

A full disk (df) is found and fixed by locating the large consumer (du), not by blind deletion.

Quick check

A service stopped and /var is at 100%. Best move?

A quick self-check — it doesn't affect your XP or progress.