Diagnosing Boot Issues
Boot Failure Classification
graph TD
A[Boot Failure Types] --> B[Hardware Issues]
A --> C[Software Configurations]
A --> D[Kernel Panic]
A --> E[Filesystem Corruption]
Tool |
Command |
Purpose |
dmesg |
dmesg | tail |
Kernel boot messages |
journalctl |
journalctl -b |
System boot logs |
systemctl |
systemctl status |
Service startup status |
Kernel Boot Log Analysis
Viewing Boot Logs
## Check kernel boot messages
sudo dmesg
## Filter recent boot messages
sudo dmesg | grep -i error
## View system boot journal
journalctl -b -p err
Identifying Boot Stages
graph LR
A[BIOS/UEFI] --> B[Bootloader]
B --> C[Kernel Loading]
C --> D[Initramfs]
D --> E[Root Filesystem]
E --> F[Service Startup]
Advanced Diagnostic Techniques
GRUB Recovery Mode
## Interrupt GRUB boot sequence
## Press 'e' during boot
## Add 'single' or 'recovery' to kernel line
Filesystem Integrity Checks
## Check filesystem
sudo fsck /dev/sda1
## Force filesystem check on next reboot
sudo touch /forcefsck
Network Boot Diagnostics
## Check network interfaces
ip addr
## Verify network connectivity
ping 8.8.8.8
Virtualization-Specific Diagnostics
VM Hypervisor Logs
## KVM/QEMU log check
sudo journalctl -u libvirtd
Troubleshooting Workflow
- Collect boot logs
- Identify error messages
- Isolate failure stage
- Determine root cause
- Apply targeted fix
Pro Tip: LabEx recommends systematic approach to VM boot troubleshooting.
Key Diagnostic Signals
- Kernel panic messages
- Filesystem mount errors
- Service startup failures
- Hardware initialization issues