LPIC-2 Linux Kernel and System Startup Practice Test 5 — 15 Questions

Question 1

A system fails to boot due to a corrupted initramfs. Which TWO methods can be used to recover? (Choose two.)

Accepted Answer

Use the rescue mode of the installation media (e.g., RHEL rescue, Ubuntu recovery). Booting from installation media (e.g., RHEL rescue or Ubuntu recovery) provides a minimal environment that can mount the root filesystem, chroot into it, and then rebuild the initramfs using the system's own kernel and modules. This method does not require a working initramfs on the disk, as the rescue environment supplies its own kernel and initial RAM disk.

Answer

Edit GRUB command line to add 'init=/bin/bash' and then rebuild initramfs from that shell

Answer

Reinstall the kernel package from the GRUB command line using a network boot

Answer

Use kexec to boot a different kernel

Question 2

Refer to the exhibit. Which module is currently in use by another module?

Accepted Answer

kvm. The `lsmod` command shows that `kvm` has a 'Used by' count of 1, indicating another module is currently using it. The 'Used by' column lists the modules that depend on the given module, so `kvm` is in use by another module (likely `kvm_intel` or `kvm_amd`). This is the correct interpretation because the question asks which module is currently in use by another module, and `kvm` is the one with a non-zero 'Used by' value.

Answer

usb_storage

Answer

kvm_intel

Answer

aesni_intel

Question 3

Refer to the exhibit. Which kernel parameter is responsible for reducing the amount of kernel messages displayed on the console?

Accepted Answer

quiet. The `quiet` kernel parameter suppresses most kernel log messages from being printed to the console during boot, reducing console output to only critical or error-level messages. This is controlled by the kernel's console log level, which `quiet` effectively lowers to KERN_WARNING (4) or higher, filtering out informational and debug messages.

Answer

ro

Answer

splash

Answer

BOOT_IMAGE

Question 4

A company has a fleet of servers running a custom Linux kernel version 5.4. They have developed several in-house kernel modules that interface with proprietary hardware. Due to a security vulnerability, the company decides to upgrade all servers to kernel version 5.10. After upgrading the kernel on a test server, the custom modules fail to load with the error 'Invalid module format' or 'disagrees about version magic'. The system administrator must resolve this issue for all servers. The modules are closed-source and cannot be modified easily. The administrator considers the following options. Question: What is the most effective course of action to load the custom modules on the new kernel?

Accepted Answer

Use modprobe with the --force-vermagic option to bypass the version check.. The most effective course of action given the constraints. The custom kernel modules are closed-source and cannot be recompiled (Option A is not feasible). The error 'Invalid module format' or 'disagrees about version magic' indicates a version magic mismatch between the module and the kernel. Using `modprobe --force-vermagic` bypasses the version magic check, allowing the module to load. Although this is a risky workaround (may lead to instability or security issues), it is the only viable option without source code access. Option C (patching the binary) is also not feasible without source, and Option D does not address the version magic mismatch.

Answer

Recompile the custom kernel modules against the new kernel headers and install them.

Answer

Update the version magic string in the module binary by patching the file.

Answer

Use systemd-modules-load to load the modules later in the boot process.

Question 5

A system administrator notices that the 'pcspkr' kernel module is causing beeps on the server console. The administrator wants to prevent this module from loading permanently. Which of the following is the correct method to blacklist the module?

Accepted Answer

Add 'blacklist pcspkr' to /etc/modprobe.d/blacklist.conf. The standard method to permanently prevent a kernel module from loading is to add a 'blacklist' directive to a file in /etc/modprobe.d/. The 'blacklist pcspkr' line tells modprobe not to load the pcspkr module automatically, even if it is requested by hardware detection or dependencies. This is the recommended approach on modern Linux distributions using modprobe's configuration system.

Answer

Add 'install pcspkr /bin/false' to /etc/modprobe.conf

Answer

Set the kernel parameter 'pcspkr=off' in GRUB

Answer

Remove the module file from /lib/modules/$(uname -r)/kernel/drivers/input/misc/

Question 6

A developer compiled a custom kernel version 5.15.10 and ran 'make modules_install' followed by 'make install' on a system using GRUB 2. After rebooting, the system still boots the old kernel. Which of the following is the most likely cause?

Accepted Answer

The boot loader configuration was not updated. After running 'make install', the GRUB 2 bootloader configuration file (usually /boot/grub/grub.cfg) is not automatically regenerated. The 'make install' target copies the kernel image and System.map to /boot, but it does not run update-grub or grub-mkconfig to add the new kernel entry. Without an updated bootloader configuration, GRUB 2 continues to boot the old kernel entry, even though the new kernel files are present.

Answer

The kernel version string is too long for GRUB 2

Answer

The kernel image was not copied to /boot because the disk was full

Answer

The initramfs was not created for the new kernel

Question 7

A system fails to boot with a kernel panic: 'Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)'. The administrator suspects the root filesystem is not being detected. Which kernel parameter should be checked first?

Accepted Answer

root=/dev/sda1. The kernel panic 'VFS: Unable to mount root fs on unknown-block(0,0)' indicates the kernel cannot locate the root filesystem. The 'root=' kernel parameter specifies the device for the root filesystem (e.g., root=/dev/sda1). Checking this parameter first is critical because if it is missing, incorrect, or the device name is wrong, the kernel will fail to mount the root filesystem and panic.

Answer

init=/sbin/init

Answer

ro

Answer

panic=10

Question 8

An administrator needs to add support for a new hardware device by compiling a kernel module. After compiling the module against the current kernel source, the module fails to load with 'modprobe: ERROR: could not insert 'mymod': Unknown symbol in module'. Which of the following is the most likely cause?

Accepted Answer

The module was compiled against a different kernel version than the running kernel. The error 'Unknown symbol in module' indicates that the module references a kernel symbol (function or variable) that is not present in the currently running kernel. This most commonly occurs when the module was compiled against a different kernel version or configuration than the running kernel, causing symbol version mismatches. The kernel's symbol versioning (CONFIG_MODVERSIONS) checks CRC values of exported symbols, and a mismatch prevents insertion.

Answer

The module has not been signed for Secure Boot

Answer

The module's dependencies are missing

Answer

The module name conflicts with a built-in driver

Question 9

Which two of the following are valid methods to pass kernel parameters during the boot process? (Choose two.)

Accepted Answer

Edit /boot/grub/grub.cfg and append parameters to the 'linux' line. Editing /boot/grub/grub.cfg to append parameters to the 'linux' line directly modifies the kernel command line that GRUB 2 passes to the Linux kernel at boot. This is a standard method for permanently adding kernel parameters like 'quiet' or 'nomodeset'.

Answer

Use the 'initrd' command in GRUB

Answer

Write the parameter directly to /proc/cmdline

Answer

Set the parameter in /etc/sysctl.conf

Question 10

Which three of the following are required steps to compile and install a custom Linux kernel from source? (Choose three.)

Accepted Answer

Run 'make modules_install' to install compiled modules. After building kernel modules with 'make', you must run 'make modules_install' to copy the compiled modules into the appropriate directory under /lib/modules/$(uname -r)/, making them available for the kernel to load. This step is essential for any kernel that uses loadable modules, as it populates the module tree with the correct .ko files.

Answer

Run 'update-grub' to regenerate GRUB configuration

Answer

Run 'depmod -a' to generate module dependencies

Question 11

A system administrator is responsible for a production server running a custom-compiled Linux kernel version 5.15. After a routine update of the kernel source and recompilation, the server fails to boot. The error message on the console is: 'Kernel panic - not syncing: No working init found. Try passing init= option to kernel.' The administrator verifies that the root filesystem is intact by booting from a live USB and mounting the root partition. The filesystem contains the usual /sbin/init (symlinked to systemd). The administrator also checks the boot loader configuration and sees that the kernel command line includes 'root=/dev/sda1 ro'. The init binary exists and is executable. Which of the following is the most likely cause of this boot failure?

Accepted Answer

The boot loader's 'initrd' directive is missing or points to a non-existent file. The error 'No working init found' indicates the kernel successfully mounted the root filesystem but could not execute the init binary. Since the administrator confirmed the init binary exists and is executable on the root partition, the most likely cause is that the kernel did not have access to the necessary drivers or modules to properly access the root filesystem at boot time. The missing or misconfigured initrd (initial RAM disk) directive means the kernel lacks the temporary root filesystem containing essential modules (e.g., storage controller drivers) needed to mount the real root filesystem, leading to the kernel falling back to a failed init search.

Answer

The kernel was compiled without support for the ext4 filesystem

Answer

The init binary is missing or corrupted

Answer

The root filesystem is corrupted and cannot be mounted properly

Question 12

A company develops a custom PCIe device driver as a kernel module. After installing a new kernel version 5.10.50 via a distribution update, the existing driver module fails to load with the error: 'insmod: ERROR: could not insert module mydriver.ko: Invalid module format'. The administrator checks the kernel version and sees that the module was compiled against a previous kernel version 5.10.45. The driver source code is available in /usr/src/mydriver. The administrator needs to get the driver working with the new kernel. Which of the following is the correct course of action?

Accepted Answer

Recompile the module using 'make -C /lib/modules/$(uname -r)/build M=/usr/src/mydriver modules'. The kernel module was compiled against a different kernel version (5.10.45) and the new kernel (5.10.50) has a different vermagic string, which includes the kernel version and other build parameters. The module must be recompiled against the new kernel's build tree located at /lib/modules/$(uname -r)/build to match the vermagic and ensure symbol compatibility. The command 'make -C /lib/modules/$(uname -r)/build M=/usr/src/mydriver modules' uses the kernel build system to compile the module against the running kernel's configuration and headers.

Answer

Copy the compiled .ko file to /lib/modules/5.10.50/kernel/drivers/misc/ and run 'depmod -a'

Answer

Edit the module's Makefile to change the version string to match the new kernel

Answer

Use 'modprobe --force mydriver' to bypass the version check

Question 13

A data center administrator is troubleshooting a server that hangs during boot after a kernel update. The server uses UEFI and GRUB 2. The administrator observes that the server displays the GRUB menu, selects the new kernel entry, but then the screen goes blank and the system does not respond. The administrator can boot the previous kernel from the GRUB menu successfully. Which of the following is the most likely cause of this issue?

Accepted Answer

The new kernel includes a graphics driver that conflicts with the hardware, causing the display to blank. The blank screen after selecting the new kernel, while the old kernel works, strongly indicates a graphics driver conflict. In GRUB 2 with UEFI, the kernel may switch from the UEFI framebuffer to a native graphics driver (e.g., nouveau, i915, amdgpu) that fails to initialize on the specific hardware, causing the display to go blank. The system is not truly hung; it continues booting without console output, which is a known issue with incompatible or buggy kernel graphics drivers.

Answer

The initramfs for the new kernel was not generated

Answer

Secure Boot is enabled and the new kernel is not signed

Answer

The new kernel's root= parameter points to an invalid device

Question 14

A company runs a high-frequency trading application that requires extremely low latency. The system administrator has compiled a custom Linux kernel with various real-time patches and tuned kernel parameters. After deploying the new kernel, the application performance degrades significantly. The administrator suspects that kernel preemption settings are causing context switch overhead. Which of the following actions should the administrator take to diagnose and optimize the kernel preemption model?

Accepted Answer

Check /proc/sched_debug for preemption counters and adjust the kernel's preemption model by recompiling with CONFIG_PREEMPT_NONE instead of CONFIG_PREEMPT. The kernel preemption model is a compile-time configuration, not a runtime parameter. To change from CONFIG_PREEMPT (full preemption) to CONFIG_PREEMPT_NONE (no forced preemption), the administrator must recompile the kernel with the appropriate configuration. Checking /proc/sched_debug can reveal preemption-related counters and context switch statistics, helping confirm that excessive preemption is causing overhead.

Answer

Use sysctl to set 'kernel.preempt_model' to 'none'

Answer

Add 'preempt=none' to the kernel command line

Answer

Change the kernel preemption model at runtime by writing to /sys/kernel/preempt_control

Question 15

A Linux system administrator is tasked with upgrading the kernel on a server running a custom compiled kernel (version 4.19) with many in-house modules. The new kernel (5.10) has significant changes, including a different API for some module functions. After compiling the new kernel and the modules, the system boots but some modules fail to load with 'Unknown symbol' errors. The administrator needs to identify which symbols are missing and fix the modules. Which of the following is the most effective approach?

Accepted Answer

Run 'modprobe --dump-modversions mymodule.ko' and compare with 'cat /proc/kallsyms' to identify mismatches. `modprobe --dump-modversions mymodule.ko` displays the symbol version (CRC) checksums for each symbol the module uses, and comparing these with `/proc/kallsyms` (which lists all symbols exported by the running kernel along with their CRC values) directly pinpoints which symbols have mismatched versions. This is the most efficient method to identify 'Unknown symbol' errors caused by API changes between kernel 4.19 and 5.10, as it reveals exactly which symbols need updating in the module source code.

Answer

Check dmesg for each module load error and recompile modules one by one

Answer

Rename the missing symbols in the source code to match the new kernel's exported symbols

Answer

Use 'nm mymodule.ko' to list all symbols and manually compare with the kernel's symbol table