LPIC-2 Practice Question: Block Devices, Filesystems and Advanced Storage
A Linux administrator notices that a newly added disk /dev/sdc is not recognized by the system. Which command should be used to rescan the SCSI bus without rebooting?
⚠ Common exam trap
Candidates often confuse the read-only /proc/scsi/scsi file with a writable interface, or assume a service restart (like 'service scsi restart') exists, when in fact the correct method uses sysfs with a specific wildcard syntax.
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
✓
echo '- - -' > /sys/class/scsi_host/host0/scan
Writing '- - -' to /sys/class/scsi_host/host0/scan triggers a SCSI bus rescan on the specified host adapter (host0) without requiring a reboot. The three dashes represent 'channel, target, LUN' wildcards, instructing the kernel to scan all SCSI IDs on that bus to detect newly added devices like /dev/sdc.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
echo 'scan' > /proc/scsi/scsi
Why it's wrong here
This command is deprecated and may not work on modern kernels.
- ✗
blockdev --rereadpt /dev/sdc
Why it's wrong here
This command re-reads the partition table, but does not rescan for new devices.
- ✗
service scsi restart
Why it's wrong here
There is no standard SCSI service; this command is invalid.
- ✓
echo '- - -' > /sys/class/scsi_host/host0/scan
Why this is correct
Writing '- - -' performs a full SCSI bus rescan without reboot.
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