EX200 Deploy, configure, and maintain systems Practice Question
A system administrator needs to ensure that a specific kernel module 'usb_storage' is not loaded automatically during boot on a RHEL 9 system. Which configuration file should be modified to blacklist this module?
⚠ Common exam trap
Many candidates confuse /etc/modules-load.d/ (used for loading modules) with /etc/modprobe.d/ (used for module configuration including blacklisting), leading them to choose Option A.
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
✓
Add 'blacklist usb_storage' to /etc/modprobe.d/blacklist.conf
On RHEL 9, the recommended way to prevent a kernel module from loading automatically is to add a 'blacklist' directive in a file under /etc/modprobe.d/. The file /etc/modprobe.d/blacklist.conf is a conventional location for such blacklist entries. When modprobe processes this file, it will ignore the specified module during boot and when loading modules manually, effectively preventing usb_storage from being loaded.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Add 'blacklist usb_storage' to /etc/modules-load.d/usb_storage.conf
Why it's wrong here
The /etc/modules-load.d/ directory is handled by the systemd-modules-load.service and is intended only to specify modules to load at boot, not to block them. A 'blacklist usb_storage' line there would be misinterpreted—either as an invalid directive or as an attempt to load a module named 'blacklist'—resulting in boot-time failures. Blacklisting belongs in modprobe configuration under /etc/modprobe.d/.
- ✗
Add 'install usb_storage /bin/false' to /etc/sysconfig/modules/
Why it's wrong here
The /etc/sysconfig/ tree is a SysVinit-era location for environment variables and service configuration, and /etc/sysconfig/modules/ is not a standard directory for module blacklist rules. Even though 'install usb_storage /bin/false' is a valid modprobe directive when placed in a modprobe.d file, the udev/modprobe machinery will never read it from this path, so the module remains loadable.
- ✓
Add 'blacklist usb_storage' to /etc/modprobe.d/blacklist.conf
Why this is correct
This is the standard and correct approach: /etc/modprobe.d/ contains configuration consumed by modprobe, and the 'blacklist' directive instructs it to ignore any request to load usb_storage from automatic discovery (e.g., udev or coldplug). Files in this directory follow a .conf naming convention, so blacklist.conf is a conventional choice. This prevents the module from being loaded by alias, though a user could still force it with an explicit full-name modprobe command.
- ✗
Add 'blacklist usb_storage' to /etc/init.d/rc.local
Why it's wrong here
The /etc/init.d/rc.local script is executed near the end of the boot sequence, after udev has already probed devices and automatically loaded needed modules—so usb_storage may have been loaded long before this line ever runs. Moreover, simply writing a 'blacklist' directive in a shell script has no effect on the kernel's module autoloading mechanism; it must be processed by modprobe in its configuration files. This option neither prevents the module from loading nor configures the system declaratively.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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