Debugging system boot issues
summary
Step‑by‑step fixes used in Red Hat support: recover a broken grub prompt by booting rescue media and rebuilding grub.cfg; diagnose initramfs/LVM failures where dracut waits up to 180s and drop to the dracut emergency shell to confirm missing VG/LV names; debug service ordering with systemctl, systemd-delta, systemctl edit and systemctl cat; inspect logs with journalctl -b and systemd-analyze; toggle SELinux to permissive via enforcing=0 for testing, then restorecon or touch /.autorelabel and reboot to fix labels.
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chapters (23)
- 0:00Introduction
- 0:40What is our job
- 4:30Agenda
- 4:52Boot Phase
- 6:37BIOS vs UEFI
- 9:55Bootloader
- 11:06Grub
- 12:38Empty grub file
- 14:30Kernel mount fail
- 15:37Init Ram FS
- 18:18Debugging process
- 19:30Where did it go
- 25:43System D
- 27:03Unit Targets
- 33:25Example
- 37:30Other options
- 41:50Fading
- 43:52Device timeouts
- 46:57Missing dependencies
- 48:38symlinks
- 49:24ordering cycles
- 51:06VC breakage
- 52:39Debugging shutdown issues
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