What is Serial Log in BIOS/UEFI?
Quick note explaining Serial Log in BIOS/UEFI for BIOS/UEFI and embedded firmware readers.
What is Serial Log in BIOS/UEFI?
A serial log is one of the most useful low-level firmware debugging outputs, especially before graphics or the OS is available.
Why it matters
- Provides a quick way to classify firmware-debug information.
- Helps narrow down whether the problem is in PEI, DXE, BDS, SMM, or OS handoff.
- Useful when reading logs, shell output, or status codes.
Practical example
Example: when boot fails, first identify the last visible phase in the log—PEI, DXE, BDS, or OS loader—before debugging individual modules.
Quick checklist
- Which phase is the last confirmed point in the log?
- Is there enough context around the failure?
- Can UEFI Shell output confirm the same state?
Quick takeaway
Serial Log in BIOS/UEFI is a small concept, but it often becomes important when reading logs or debugging real firmware.
Related notes
- UEFI Shell Commands: key points
- S3 Resume Debug Quicknote
- What is POST Code?
- PEI Fail Checklist
- DXE Dependency Checklist
Public references
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