Boot Issues

A system that fails to boot is one of the most stressful types of failure. This article covers troubleshooting and repair methods for common boot issues including GRUB boot repair, rescue mode usage, fstab error diagnosis, and dracut problems.

Boot Process Overview

The boot flow of an EL system:

1. Firmware (BIOS/UEFI) — Hardware self-test, loads the bootloader
2. GRUB2 — Reads configuration, loads kernel and initramfs
3. Kernel — Initializes hardware, mounts initramfs
4. dracut/initramfs — Loads drivers, mounts the root filesystem
5. systemd — Starts targets and services

Failures at different stages have different symptoms and solutions.

GRUB Rescue Mode

When GRUB cannot find its configuration file or modules, it drops to the grub rescue> prompt.

Symptoms

The screen displays:

error: no such partition.
Entering rescue mode...
grub rescue>

Troubleshooting Steps

List available disks and partitions

grub rescue> ls

This displays output like (hd0) (hd0,msdos1) (hd0,msdos2).

Search each partition for the grub directory

grub rescue> ls (hd0,msdos1)/boot/grub2/
grub rescue> ls (hd0,msdos2)/boot/grub2/

Once you find the partition containing the GRUB files:

Set the prefix and root partition

grub rescue> set prefix=(hd0,msdos1)/boot/grub2
grub rescue> set root=(hd0,msdos1)

Load the normal module and boot

grub rescue> insmod normal
grub rescue> normal

After the system boots, immediately repair the GRUB configuration:

Reinstall GRUB (BIOS systems)

$ sudo grub2-install /dev/sda
$ sudo grub2-mkconfig -o /boot/grub2/grub.cfg

Reinstall GRUB (EFI systems)

$ sudo dnf reinstall grub2-efi-x64 shim-x64
$ sudo grub2-mkconfig -o /boot/efi/EFI/$(. /etc/os-release && echo $ID)/grub.cfg

Emergency Mode

Emergency mode is triggered when systemd cannot complete basic initialization, such as when /etc/fstab contains a filesystem that cannot be mounted.

Symptoms

The screen displays:

Welcome to emergency mode! After logging in, type "journalctl -xb" to view
system logs, "systemctl reboot" to reboot, "systemctl default" to try again
to boot into default mode.
Give root password for maintenance
(or press Control-D to continue):

Troubleshooting Steps

After logging in with the root password:

View boot log errors

$ journalctl -xb --priority=err

Check fstab for problematic mount entries

$ cat /etc/fstab

Try manually mounting all filesystems

$ mount -a 2>&1

If a specific partition is causing the problem:

Check disk and partition status

$ lsblk -f
$ blkid

After fixing the issue:

Reboot the system

$ systemctl reboot

Rescue Mode

Rescue mode boots from installation media and is used to repair a system that cannot start.

Entering Rescue Mode

1. Boot from an AlmaLinux / Rocky Linux installation ISO
2. Select Troubleshooting from the boot menu
3. Select Rescue a system

The system will detect the installed OS and mount it to /mnt/sysimage.

Switch to the installed system environment

$ chroot /mnt/sysimage

You can now execute repair commands as if you were on the normal system.

Manual Mounting (if auto-detection fails)

View available partitions

$ lsblk -f

Manually mount the root partition

$ mount /dev/sda2 /mnt/sysimage

Mount the boot partition

$ mount /dev/sda1 /mnt/sysimage/boot

Mount necessary virtual filesystems

$ mount --bind /dev /mnt/sysimage/dev
$ mount --bind /proc /mnt/sysimage/proc
$ mount --bind /sys /mnt/sysimage/sys
$ mount --bind /run /mnt/sysimage/run

chroot into the system

$ chroot /mnt/sysimage

Single User Mode

Single user mode is used to troubleshoot issues in a minimal environment, such as resetting the root password.

Entering Single User Mode via GRUB

1. Press e at the GRUB boot menu to edit the boot entry
2. Find the line starting with linux (containing vmlinuz)
3. Append to the end of that line: rd.break or init=/bin/bash
4. Press Ctrl+X to boot

Resetting the Root Password with rd.break

Remount the root filesystem as read-write

switch_root:/# mount -o remount,rw /sysroot

Switch to the system root directory

switch_root:/# chroot /sysroot

Reset the root password

sh-4.4# passwd root

If SELinux is in enforcing mode, trigger a relabel

sh-4.4# touch /.autorelabel

Exit and reboot

sh-4.4# exit
switch_root:/# exit

Note: touch /.autorelabel triggers a relabel of the entire filesystem’s SELinux labels on the next boot. This process may take anywhere from a few minutes to tens of minutes depending on the number of files. Do not force a shutdown during this process.

Viewing Boot Logs

Using journalctl

View current boot logs

$ journalctl -b

View previous boot logs

$ journalctl -b -1

View only error-level boot logs

$ journalctl -b -p err

List all available boot records

$ journalctl --list-boots

Using dmesg

View kernel ring buffer messages

$ dmesg | less

View only errors and warnings

$ dmesg --level=err,warn

View storage-related messages

$ dmesg | grep -i -E '(sd[a-z]|nvme|ata|scsi)'

Enabling Persistent Logging

By default, journald logs on EL systems may not be persisted. Enabling persistence allows you to view previous boot logs:

Create the persistent log directory

$ sudo mkdir -p /var/log/journal
$ sudo systemd-tmpfiles --create --prefix /var/log/journal
$ sudo systemctl restart systemd-journald

Fixing fstab Errors

Errors in /etc/fstab are a common cause of boot failures.

Common fstab Issues

• UUID does not match the actual partition (after disk replacement)
• References a non-existent partition
• Incorrect mount options
• NFS/CIFS remote mounts attempted before network is ready

Troubleshooting

View the current disk UUIDs

$ blkid

Compare with the UUIDs in fstab

$ cat /etc/fstab

Verify fstab for syntax errors

$ sudo findmnt --verify --tab-file /etc/fstab

Repair Example

If a partition’s UUID has changed:

Get the new UUID with blkid and update fstab

$ sudo blkid /dev/sda2

Example output: /dev/sda2: UUID="xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"

Edit fstab and replace the old UUID

$ sudo vi /etc/fstab

Preventing NFS Mounts from Blocking Boot

For network filesystem mounts, add the _netdev and nofail options:

server:/export  /mnt/nfs  nfs  defaults,_netdev,nofail  0  0

nofail ensures the system boots normally even if the mount fails. _netdev ensures the mount waits for the network to be ready.

Reinstalling GRUB

BIOS Systems

Reinstall GRUB to the MBR

$ sudo grub2-install /dev/sda

Regenerate the GRUB configuration file

$ sudo grub2-mkconfig -o /boot/grub2/grub.cfg

EFI Systems

Reinstall EFI boot files

$ sudo dnf reinstall grub2-efi-x64 shim-x64

Regenerate GRUB configuration

$ sudo grub2-mkconfig -o /boot/efi/EFI/$(. /etc/os-release && echo $ID)/grub.cfg

Verify EFI boot entries

$ efibootmgr -v

Reinstalling GRUB from Rescue Mode

If the system is completely unable to boot, after entering rescue mode from installation media:

chroot into the system (assuming it is mounted at /mnt/sysimage)

$ chroot /mnt/sysimage

Reinstall kernel and GRUB (BIOS)

$ dnf reinstall kernel-core
$ grub2-install /dev/sda
$ grub2-mkconfig -o /boot/grub2/grub.cfg

Reinstall kernel and GRUB (EFI)

$ dnf reinstall kernel-core grub2-efi-x64 shim-x64
$ grub2-mkconfig -o /boot/efi/EFI/$(. /etc/os-release && echo $ID)/grub.cfg

Dracut / Initramfs Issues

dracut is responsible for generating the initramfs (initial RAM filesystem), which contains the drivers and tools needed during the boot stage.

Symptoms

• dracut-initqueue timeout during boot
• Cannot find root filesystem
• Drops into the dracut emergency shell

dracut-initqueue[xxx]: Warning: dracut-initqueue timeout
dracut-initqueue[xxx]: Warning: Could not boot.

Troubleshooting Steps

View available disks in the dracut shell

dracut:/# ls /dev/sd* /dev/nvme*

View dracut logs

dracut:/# journalctl

Regenerating initramfs

Regenerate initramfs for the current kernel

$ sudo dracut --force

Regenerate for a specific kernel version

$ sudo dracut --force /boot/initramfs-$(uname -r).img $(uname -r)

Include additional driver modules

$ sudo dracut --force --add-drivers "megaraid_sas mpt3sas" /boot/initramfs-$(uname -r).img $(uname -r)

Common dracut Issues

Missing storage drivers: If the storage controller was changed or the VM was migrated to a different platform:

List modules included in the initramfs

$ lsinitrd /boot/initramfs-$(uname -r).img | grep -i driver

Add virtio drivers (for KVM/QEMU virtual machines)

$ sudo dracut --force --add-drivers "virtio_blk virtio_scsi virtio_net virtio_pci"

Corrupted initramfs file:

Check initramfs file size (should be at least tens of MB)

$ ls -lh /boot/initramfs-*.img

If the file size is abnormal (e.g., only a few KB), the file is corrupted and needs to be regenerated.

Unable to Boot After Kernel Upgrade

Rolling Back to an Older Kernel

1. Select the older kernel version from the GRUB boot menu
2. If the GRUB menu does not appear (countdown too short), repeatedly press Esc or hold Shift during boot

After booting the old kernel, view installed kernels

$ rpm -qa kernel-core | sort -V

Set the default kernel back to the old version

$ sudo grubby --set-default /boot/vmlinuz-<old-kernel-version>

Remove the problematic new kernel

$ sudo dnf remove kernel-core-<problematic-version>

Further Reading

• Network Issues Troubleshooting
• Performance Troubleshooting
• Common Errors Quick Reference