linuxexpert-practice-labs/labs/linux-plus/1-2-1-kernel-modules-and-initrd

Linux+ 1.2.1: Kernel modules and the initrd

Looking at modules, loading one with an option, loading it at every boot, and finding the root disk's driver in the initrd.

Before you start

The lab unloads the dummy module, a harmless one that makes network devices. Reboot when task 3 says so; the check looks at the running system.

Tasks

1. Find the license of the xfs module and write it to /root/lab-answers/1.
2. Load dummy with the option numdummies=3, check that it made three devices, and unload it again. Not graded: ip -br link show type dummy | wc -l should print 3 before you unload it.
3. Make dummy load at every boot with the option numdummies=1, then reboot. After the reboot, ip -br link show type dummy shows exactly one device. Keep your files until you've run le-lab check; reset removes them.
4. Look inside your initrd, and find the driver for your root disk (virtio_blk, nvme or ahci, for example). Write its name to /root/lab-answers/4.

Hints

• lsmod, modinfo xfs, modinfo -F license.
• modprobe dummy numdummies=3, modprobe -r dummy.
• /etc/modules-load.d/ for loading, /etc/modprobe.d/ for options. Files in every modprobe.d directory are read in name order and the last setting wins; modprobe --show-depends dummy shows what modprobe will pass.
• lsinitrd on the RHEL family, lsinitramfs /boot/initrd.img-$(uname -r) on Ubuntu, which builds virtio_blk into the kernel: grep virtio_blk /lib/modules/$(uname -r)/modules.builtin. lsblk shows the root disk.