A systemd-based machine fails during a normal boot because a service hangs. At the boot loader menu you want to edit the kernel command line for this one boot so the system comes up in single-user rescue mode instead. Which parameter do you append?
LPIC-1 Exam 101-500, objective 101. System architecture hard
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The options
Not correct init=/bin/bash
Wrong for this goal, though it is a real and sometimes useful parameter: it replaces PID 1 with a shell, so no services start at all, no filesystems beyond root are mounted, and root is typically still read-only.
Correct systemd.unit=rescue.target
Correct. This tells systemd which unit to isolate as the initial target, so it brings up the minimal rescue environment rather than the default target, for this boot only.
Not correct quiet
Wrong. quiet only lowers the console log level so kernel messages are hidden during boot. It has no effect on which services start.
Not correct ro
Wrong. ro tells the kernel to mount the root filesystem read-only initially, which is the normal default anyway; it is remounted read-write later in the boot.
Why
systemd reads systemd.unit= from the kernel command line to choose its initial target, so systemd.unit=rescue.target (or emergency.target for an even more minimal shell) is the modern way to boot into maintenance mode for one boot. systemd also still honours the legacy words single, s and 1 by mapping them to rescue.target. init=/bin/bash bypasses systemd entirely and is a last resort, for example when you need to reset a forgotten root password.
Where this comes from
- Cited
- LPI exam objective 101.2
- What it says
- Passing parameters to the kernel and to the init system at boot time.
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.
More questions on this objective
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