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Unofficial practice

Storage Usage First Response

A host reports write errors or low-space warnings. Prove the pressured mount point first, then decide whether bytes, inodes, or the wrong filesystem are the real issue.

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Try first

df -h && df -i && du -xhd1 /var | sort -h

Troubleshooting ladder

  1. Name the symptom.
  2. Inspect read-only state.
  3. Find the owner, service, file, device, mount, or route.
  4. Read the decisive output field.
  5. Choose the next narrow command.
  6. Avoid broad or destructive changes.
  7. Make the smallest justified change if required.
  8. Verify and record what changed.

drill evidence

Sample output and answer key

Command anatomy

df -h && df -i && du -xhd1 /var | sort -h
df
summarize filesystem pressure
-h
human-readable byte usage
-i
inode usage instead of bytes
target
scope the question to a mount point

Annotated output

Filesystem      Size  Used Avail Use% Mounted on
/dev/nvme0n1p2   40G   39G  220M 100% /
/dev/nvme0n1p3  200G   82G  118G  42% /home

Filesystem      Inodes  IUsed   IFree IUse% Mounted on
/dev/nvme0n1p2 2621440 2621400     40  100% /

4.0K	/var/tmp
180M	/var/log
2.8G	/var/lib

What to notice

filesystem
the device or volume under pressure
mounted on
the scope of the problem
Use%
byte pressure
IUse%
inode pressure
Avail/IFree
how much room remains
/var child
which top-level directory is growing inside the likely hot path

Safe vs unsafe move

Common wrong move

Cleaning /home when / is the full filesystem.

Next safe command

sudo find /var -xdev -type f -size +100M -printf '%s %p\n' 2>/dev/null | sort -nr | head

Goal

Prove the condition with command output before changing the system.

Safe first command

df -h && df -i && du -xhd1 /var | sort -h

Correct interpretation

The decisive fields are `Mounted on`, `Use%`, and `IUse%`. The root filesystem is full, not `/home`, and `/var/lib` is the first hot path to inspect. The next safe command stays on `/var` with `-xdev` so you do not wander across other filesystems before proving what is large.

Next safe command

sudo find /var -xdev -type f -size +100M -printf '%s %p\n' 2>/dev/null | sort -nr | head

Common wrong move

Cleaning /home when / is the full filesystem.

Self-check

Which mount point is actually full, is the pressure bytes or inodes, and which scoped read-only command should you run before removing files?

source and objective

Related cert objective

Source status: Linux Foundation LFCS page verified June 30, 2026. LFCS is an online, proctored, performance-based command-line exam.

Open related practice area

Related command pages

Why this matters

The point is not to memorize a flag. It is to read the evidence, name the next safe check, and avoid the tempting broad fix.