Windows Component Based Servicing Log File (C:\Windows\Logs\CBS\CBS.log)

Bottom Line: It is safe to delete CBS.log and compressed CbsPersist_*.cab log files. Windows writes servicing log entries to C:\Windows\Logs\CBS\CBS.log during Windows Update, DISM, and SFC commands.

Why Does Windows CBS.log Exist?

The Component Based Servicing (CBS) engine logs system component updates, package installations, and system file repairs (sfc /scannow).

• Primary Purpose: Diagnostic logging for Windows Update and DISM servicing tasks.
• Storage Bug: A known Windows bug can cause Makecab.exe to fail during CBS log compression, creating endless multi-gigabyte CbsPersist_*.cab archive files (1 GB to 15 GB).

What Happens If You Delete CBS.log?

• System Safety: ✅ 100% Safe to Delete. Windows Update and DISM remain fully functional.
• Automatic Re-creation: Windows automatically creates a fresh CBS.log file on the next servicing task.
• Reclaimed Storage: Reclaims 1 GB to 15 GB of storage space.

How to Delete CBS.log Safely

Step 1: Stop Windows Modules Installer service

net stop trustedinstaller

Step 2: Delete CBS.log and archived CbsPersist CAB files

del /f /q C:\Windows\Logs\CBS\CBS.log
del /f /q C:\Windows\Logs\CBS\CbsPersist_*.cab

Step 3: Restart service

net start trustedinstaller

Frequently Asked Questions (FAQ)

Why does Windows say “File is open in TrustedInstaller”?

Stop the trustedinstaller service before deleting CBS.log so the file lock is released.