Boot targets, and a system that will not boot
The tasks that end an exam attempt are the ones that stop a machine booting, and almost all of them are a bad /etc/fstab line. This guide reads what the last boot actually did, covers the two rescue targets and how to reach them from GRUB, and then diagnoses a genuinely failed mount on this host from the failed unit back to the line that caused it.
Operations Deployment Guide 17 of 38 Advanced
- PlatformsUbuntu 26.04 LTS + AlmaLinux 10.2
- LVM2.03.31 (Ubuntu) / 2.03.36 (AlmaLinux)
- nftables1.1.6 (Ubuntu) / 1.1.5 (AlmaLinux)
- TimeAbout 20 min
RHEL 10 with GRUB2 and BLS entries, so grubby is the tool here. Debian and Ubuntu use update-grub and /boot/grub/grub.cfg instead - the systemd half of this page is identical on both, the bootloader half is not.
- Firewallufw 0.36.2 enabled but reporting inactive / firewalld active
- Network confignetplan + systemd-networkd / NetworkManager 1.56.0
| Server Name | IP Address | OS | Roles | CPU | RAM | HDD |
|---|---|---|---|---|---|---|
| LFCS-A01 | 192.168.0.70 | Ubuntu 26.04 LTS | Primary host - most guides run only here | 2 Core | 4 GB | 50 GB |
| LFCS-C01 | 192.168.0.72 | AlmaLinux 10.2 | The other distribution - dnf, firewalld and NetworkManager | 2 Core | 4 GB | 50 GB |
This guide includes
Use this because the tasks that end an exam attempt are the ones that stop a machine booting. This matters because one bad fstab line strands the host - and two commands check it before the reboot that would.
- finding what this machine boots into, and what the boot actually did
- reading the bootloader configuration, and what the kernel was given
- using the two rescue targets, and seeing what each one gives you
- tracing a failed mount back to the line that caused it
- checking fstab before the reboot that would strand you, on both families
Before you start
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What this machine boots into
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What the boot actually did
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The bootloader, and what the kernel was given
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The targets you boot into when something is broken
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A failed mount, traced back to the line that caused it
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Checking fstab before the reboot that would strand you
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The bootloader lives somewhere else on Ubuntu