EX200 Create and configure file systems Practice Question
A system administrator needs to verify that the filesystem on /dev/sdb1 is ext4 before adding it to /etc/fstab. Which command provides this information?
⚠ Common exam trap
A common mix-up: candidates choose `df -Th` because it shows filesystem type, but they forget that it only works on mounted filesystems, whereas `lsblk -f` works on unmounted devices as well.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
lsblk -f /dev/sdb1
The `lsblk -f /dev/sdb1` command displays the filesystem type (FSTYPE) for the specified block device, such as ext4. This is the most direct and reliable way to verify the filesystem on a specific partition before adding it to /etc/fstab.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
mount -a
Why it's wrong here
mount -a is an action command that mounts every entry in /etc/fstab with the auto option; it does not print or query filesystem type metadata. Running it also risks errors if /dev/sdb1 is already mounted or not listed in fstab, so it cannot serve as a verification step. To confirm the filesystem type, you need a read-only command that inspects the superblock, not one that mutates the mount table.
- ✗
df -Th /dev/sdb1
Why it's wrong here
df -Th /dev/sdb1 works only when the device is currently mounted, because df reads the kernel's mount table (e.g., /proc/mounts) to display filesystem type, size, and usage. If /dev/sdb1 is unmounted, df either reports an error or simply shows nothing for that device. It also depends on the existing mount and does not directly probe the on-disk superblock, so it cannot reveal the type of an unmounted or unrecognized filesystem.
- ✗
fdisk -l /dev/sdb1
Why it's wrong here
fdisk -l /dev/sdb1 displays the partition table, including partition type IDs such as 83 (Linux) or 82 (swap), but that is merely a partitioning hint and does not reflect the actual filesystem written by mkfs. When given a partition device like /dev/sdb1, fdisk may even complain that the device has no valid partition table, because partitions are not expected to contain one. It never reads the filesystem superblock, so it cannot report ext4, xfs, or other filesystem types.
- ✓
lsblk -f /dev/sdb1
Why this is correct
lsblk -f /dev/sdb1 is correct because the -f (--fs) option makes lsblk output the filesystem type, label, UUID, and mount point for the specified block device. It reads this information from udev and kernel device da, which ultimately come from the filesystem superblock, so it works whether the device is mounted or not. This makes it ideal for verifying that /dev/sdb1 was formatted with the expected filesystem before attempting to mount it.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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