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Linux Boot Failure Troubleshooting (Enterprise Level) - Coggle Diagram
Linux Boot Failure Troubleshooting (Enterprise Level)
Linux Boot Failure
Definition
System fails to complete boot process
May stop at BIOS/UEFI, GRUB, Kernel, Initramfs, or Systemd stage
Requires structured troubleshooting approach
Enterprise Troubleshooting Flow
Identify Failure Stage
BIOS/UEFI
Boot Loader (GRUB)
Kernel Loading
Initramfs
Root Filesystem Mount
Systemd Services
Login Screen
Collect Evidence
Error Messages
Console Output
Last Changes
Recent Patching
Hardware Changes
Storage Changes
Stage 1 - BIOS/UEFI Issues
Symptoms
No Boot Device Found
PXE Boot Loop
Black Screen
Disk Not Detected
Checks
Verify Disk Detection
Verify Boot Order
Verify RAID Status
Verify UEFI/Legacy Mode
Commands
lsblk
fdisk -l
Enterprise Actions
Check Hardware Monitoring Tools
Check RAID Controller Logs
Verify SAN LUN Visibility
Stage 2 - GRUB Bootloader Failure
Symptoms
grub rescue>
GRUB Prompt
Missing Boot Entries
Common Causes
Corrupted GRUB
Deleted Boot Partition
Disk Changes
Failed Updates
Commands
ls
set
insmod normal
normal
Recovery
Boot Rescue Mode
Chroot Into System
Reinstall GRUB
RHEL
grub2-install /dev/sda
grub2-mkconfig -o /boot/grub2/grub.cfg
Ubuntu
grub-install /dev/sda
update-grub
Enterprise Actions
Maintain Golden Images
Backup Boot Partitions
Document Boot Layout
Stage 3 - Kernel Panic
Symptoms
Kernel Panic Message
System Freeze
Automatic Reboot Loop
Common Causes
Missing Kernel Modules
Corrupted Kernel
Driver Failure
Storage Driver Issue
Investigation
Boot Older Kernel
Review Console Logs
Verify Installed Kernels
Commands
uname -r
rpm -qa | grep kernel
dpkg -l | grep linux-image
Enterprise Actions
Keep Multiple Kernels Installed
Test Kernel Updates In Staging
Use Change Management
Stage 4 - Initramfs Failure
Symptoms
dracut Emergency Shell
BusyBox Prompt
Cannot Find Root Device
Causes
Missing Drivers
Broken Initramfs
Storage Configuration Change
Commands
lsblk
blkid
cat /proc/cmdline
Recovery
Rebuild Initramfs
RHEL
dracut -f
Ubuntu
update-initramfs -u
Enterprise Actions
Verify Multipath Configuration
Verify SAN Drivers
Validate Initramfs After Updates
Stage 5 - Root Filesystem Mount Failure
Symptoms
Cannot Mount Root Filesystem
Read Only Filesystem
UUID Not Found
Causes
Disk Failure
Incorrect UUID
Corrupted Filesystem
Missing LVM
Commands
lsblk
blkid
vgscan
vgchange -ay
lvscan
Filesystem Repair
fsck /dev/sdaX
xfs_repair /dev/sdaX
Enterprise Actions
Monitor Disk Health
Backup Critical Systems
Validate Storage Migrations
Stage 6 - LVM Problems
Symptoms
Root Volume Missing
Logical Volume Not Found
Investigation
pvscan
vgscan
lvscan
Recovery
vgchange -ay
Enterprise Actions
Backup LVM Metadata
Document Volume Layout
Stage 7 - Encryption (LUKS) Problems
Symptoms
LUKS Unlock Failure
Wrong Passphrase
Missing Key
Commands
cryptsetup luksDump /dev/sdaX
cryptsetup luksOpen /dev/sdaX luksroot
Recovery
Use Recovery Key
Restore Key Slot
Enterprise Actions
Centralized Key Management
TPM Integration
Clevis + Tang Deployment
Stage 8 - Filesystem Corruption
Symptoms
Read-only Filesystem
I/O Errors
Missing Files
EXT4 Repair
fsck -y /dev/sdaX
XFS Repair
xfs_repair /dev/sdaX
Enterprise Actions
Storage Monitoring
Snapshot Strategy
Backup Verification
Stage 9 - Systemd Service Failures
Symptoms
Boot Stops During Startup
Emergency Mode
Dependency Failures
Investigation
systemctl --failed
journalctl -xb
Recovery
Disable Problem Service
Fix Dependency Chain
Commands
systemctl disable service_name
systemctl restart service_name
Enterprise Actions
Monitor Critical Services
Use Service Dependency Documentation
Stage 10 - SELinux Issues
Symptoms
Services Fail To Start
Permission Denied Errors
Investigation
sestatus
ausearch -m avc
Temporary Test
setenforce 0
Relabel Filesystem
touch /.autorelabel
Enterprise Actions
Use Proper SELinux Policies
Avoid Permanent Disablement
Stage 11 - Network Related Boot Issues
Symptoms
Remote Server Unreachable
Boot Delays
Commands
ip addr
nmcli
systemctl status NetworkManager
Enterprise Actions
Validate NIC Teaming
Validate Bonding
Verify VLAN Configurations
Log Analysis
Journal Logs
journalctl -xb
Previous Boot
journalctl -xb -1
Kernel Logs
dmesg
Service Logs
systemctl status service_name
Rescue Mode
Access
GRUB Menu
Recovery Mode
Rescue ISO
Tasks
Reset Password
Repair Filesystem
Rebuild GRUB
Repair LVM
Rebuild Initramfs
Enterprise Recovery Strategy
Backup Before Changes
Maintain Recovery ISO
Keep Multiple Kernels
Test Patches In Non-Production
Maintain Configuration Management
Automate Recovery Procedures
Document Every Change
Enterprise Tools
Ansible
Automated Recovery Tasks
Configuration Enforcement
Monitoring
Nagios
Zabbix
Prometheus
Logging
ELK Stack
Wazuh
Syslog Servers
Interview Questions
What are Linux Boot Stages?
BIOS/UEFI
GRUB
Kernel
Initramfs
Systemd
Login
What is Kernel Panic?
Kernel Unable To Continue Execution
How To Repair GRUB?
grub-install
grub2-mkconfig
How To Repair Initramfs?
dracut -f
update-initramfs -u
How To Check Failed Services?
systemctl --failed
How To View Boot Logs?
journalctl -xb
How To Activate Missing LVM Volumes?
vgchange -ay
How To Repair Filesystem?
fsck
xfs_repair
Golden Rule
Identify Failure Stage First
Never Guess
Collect Logs
Verify Storage
Verify Bootloader
Verify Kernel
Verify Filesystem
Restore Service Availability
Document Root Cause