A GRUB menu entry ends with the directives 'set root=(hd0,3)' followed by 'chainloader +1'. What is GRUB doing?
LPIC-1 Exam 101-500, objective 102. Linux installation and package management hard
Machine-checked — no person has signed for it. This question was read against the source cited below by an automated pass, which found no contradiction. That is a weaker claim than it sounds: the same kind of process wrote the question, so it can confirm its own mistake.
Treat it as a good draft rather than as settled fact, and read the source below before you rely on it. It is not used in mock exams here — only questions a person has signed for are.
How these questions are written — where each question comes from, what the verification ledger records, and what happens when one is found wrong.
The options
Not correct Mounting that partition as the root filesystem for the booted system
Wrong. GRUB's 'root' variable only tells GRUB where to look for its own files. The kernel's root filesystem comes from the root= parameter on the kernel command line.
Not correct Loading the Linux kernel found on that partition into memory
Wrong. Loading a Linux kernel uses the linux directive (kernel in GRUB Legacy), which names a kernel file and passes it command-line parameters.
Correct Loading the boot sector of that partition and handing control to whatever boot loader is stored there
Correct. chainloader +1 reads the first sector of the selected device and transfers control to it — the standard way to boot another operating system's own boot loader.
Not correct Adding one second to the menu timeout before the default entry boots
Wrong. The timeout is set by the timeout variable in grub.cfg (from GRUB_TIMEOUT in /etc/default/grub); the +1 here is a block-list meaning 'the first sector'.
Why
Chainloading is how GRUB boots a foreign boot loader instead of a kernel: it loads sector 1 of the target device (the '+1' block list is one block starting at offset 0) and jumps to it. Note the partition numbering difference between versions — GRUB Legacy numbered partitions from 0, so the first partition on the first disk was (hd0,0), while GRUB 2 numbers partitions from 1, making it (hd0,1). Disks are numbered from 0 in both.
Where this comes from
- Cited
- LPI exam objective 102.2
- What it says
- Awareness of chainloading another boot loader from GRUB.
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 102 and space the ones you get wrong.
More questions on this objective
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- You are laying out storage for a general-purpose Linux server. Which TWO of the following are genuine reasons to use LVM for the data filesystems rather than plain partitions? machine-checked
- Which file is the configuration file that GRUB 2 generates, and which administrators are told not to edit by hand on a typical Linux distribution? machine-checked
- You replaced the boot disk in a BIOS/MBR system and need to write the GRUB 2 boot loader into the master boot record of /dev/sda, installing the required GRUB modules under /boot. Which command does that? machine-checked
- On a GRUB 2 system whose configuration file is /boot/grub/grub.cfg, type the grub-mkconfig command — including the option and its argument — that regenerates that file. machine-checked