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Unofficial practice

Mount Readout with findmnt

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

findmnt -T /srv || df -h /srv

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

findmnt -T /srv || df -h /srv
findmnt
show the mount that contains a target path
df
fallback filesystem capacity check when present
TARGET
the mount point being used
FSTYPE
the filesystem type
OPTIONS
read/write and behavior flags

Annotated output

TARGET SOURCE         FSTYPE OPTIONS
/      /dev/nvme0n1p2 ext4   rw,relatime
/var   /dev/nvme0n1p4 ext4   rw,relatime
/srv   tank/srv       zfs    rw,relatime

What to notice

TARGET
the mount point being used
SOURCE
the backing device or dataset
FSTYPE
filesystem type
OPTIONS
read/write and behavior flags

Safe vs unsafe move

Common wrong move

Assuming a path is on / when it is a separate mount.

Next safe command

df -hT /srv

Goal

Prove the condition with command output before changing the system.

Safe first command

findmnt -T /srv || df -h /srv

Correct interpretation

The decisive fields are `TARGET`, `SOURCE`, `FSTYPE`. The affected object is the exact target named in the output, not the broad subsystem around it. The next safe command is `df -hT /srv` because it narrows the evidence without jumping to a broad fix. Watch out for this wrong move: Assuming a path is on / when it is a separate mount.

Next safe command

df -hT /srv

Common wrong move

Assuming a path is on / when it is a separate mount.

Self-check

Which mount point is actually under pressure, and does the output prove byte usage, inode usage, or both?

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.