On a Red Hat family server you moved the root filesystem onto an LVM logical volume and updated the kernel's root= argument accordingly. The next boot stops in an emergency shell with 'unable to find a live root filesystem'. Which command addresses the cause?
LPIC-1 Exam 101-500, objective 101. System architecture hard
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The options
Correct dracut -f
Correct. It rebuilds the initramfs for the running kernel so that the device-mapper modules and the LVM activation logic are present in the early boot image.
Not correct update-initramfs -u
Wrong here: right idea, wrong distribution. update-initramfs is the Debian and Ubuntu tool, and it is not present on Red Hat family systems, which use dracut.
Not correct depmod -a
Wrong. depmod refreshes the module dependency index inside /lib/modules on the real root filesystem. That tree is unreachable at the moment of failure, because the real root is exactly what cannot be mounted.
Not correct grub2-mkconfig -o /boot/grub2/grub.cfg
Wrong for this symptom. Regenerating the menu would matter if the kernel arguments were wrong, but the stem says root= is already correct; the kernel started and then failed to reach the volume.
Why
The initramfs is a self-contained early userspace whose only job is to make the real root filesystem reachable and then hand over to it. Anything needed to get there — device-mapper and LVM, RAID assembly, LUKS unlocking, an exotic storage or filesystem driver — must be inside the image, because at that point nothing on the root filesystem can be read. Changing the storage layout under the root filesystem therefore always means regenerating the image: dracut -f on Red Hat family systems, update-initramfs -u -k all on Debian family ones.
Where this comes from
- Cited
- manual page dracut(8)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 101 and space the ones you get wrong.
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