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Windows 7: large size CBS.log files creating, was never before

29 May 2015   #1

Windows 7 Ultimate x64
large size CBS.log files creating, was never before

Recently when I use favorite ccleaner software to clean my temp files, I notice that there is large size file is creating by name of CBS.log in C:\Windows\Logs\CBS with size of 200 MB or more.
I never had this issue before and it seems that this causes a high usage of cpu and hard drive speed,which causes affect on my gaming experience or other works.
do anyone has any idea why it's creating and why so large? also any suggest to prevent it?

My System SpecsSystem Spec
29 May 2015   #2

Windows 10 Pro X64

CBS.log is where SFC (System File Cleaner) among others writes it's information. 200MB is not a lot so I wouldn't be too concerned.
My System SpecsSystem Spec
29 May 2015   #3

Windows 7 Ultimate x64 SP1

Copy pasted if sounds a little off, so bear with me:

Hey, there is a known issue with a recent Windows Update (KB3022345), it causes an irrepairable corruption warning (which is a false report, the files are not corrupt in reality). If you have this update installed then do one of the following:
- Uninstall this update (it is Windows 10 preparation update) or
- Run the fix from

After the above, run another SFC /scannow. If you still get a corruption, attach it in your next post.

Check your CBS.log afterwards, I did have a large log also and corrected after fixing and rerunning the scan. maybe it will help you too. If it doesn't Ztrucker already gave you the answer.
My System SpecsSystem Spec

31 May 2015   #4

Microsoft Community Contributor Award Recipient

Win 7 x64 Home Premium (and x86 VirtualBox VM)/Win10

The CBS.log file should NOT be removed - it contains vital diagnostic data.
It's also almost permanently in use by the System account.
It grows to a point, and is then archived by the system into the CBSPersist.CAB files you'll find in the same folder.
I have occasionally seen the CBS log get out of control and grow to over 2GB - but this is rare.
150-200MB is not unusual, and usually compresses down to around 10MB as a CAB file on archiving.

I'd leave all the files in the C:\Windows\Logs folder well alone - they don't really take up all that much space. If your system actually does need that space, then it's time for a new hard drive!
My System SpecsSystem Spec
26 Oct 2015   #5

Windows 7 Home Premium and Enterprise x64

My CBS folder was over 10GB, with two 3.5GB CBS log files, two 1.75 to 1.8 GB log files, and a few 500 to 700 MB log files. Needless to say, I blew all but the most recent CBS log file away.
My System SpecsSystem Spec
28 Oct 2015   #6

Microsoft Community Contributor Award Recipient

Win 7 x64 Home Premium (and x86 VirtualBox VM)/Win10

You can delete the oversized CBS log files (over about 800MB) - they are likely to be totally confusing, even if I could actually read them in a decent viewer. Files of that size, I have to use a Hex viewer for , and then trim out anything outside the first and last error statement, and hope that I can read the rest.

How big is the current CBS.log?
My System SpecsSystem Spec
01 Dec 2015   #7

Windows 7 Ultimate x64

@NoelDP - I'm having a similar, albeit more extreme, problem. Using WinDirStat, I have identified that the C:\Windows\Logs\CBS on my machine is now at 106 GB. My CBS.log file has grown to 8.3 GB, and I have a few CbsPersist_[x].log files >5 GB.

Does anyone have a thought as to a root cause here? I've seen recommendations elsewhere to disable TrustedInstaller.exe, delete all the logs, and then re-enable the .exe file. Source: windows 8 - Why is CBS.log file size 20 GB - Super User
My System SpecsSystem Spec
01 Dec 2015   #8

Windows 7 x64 running Paralles on a 2015 MacBook Air
Large CBS

I have a 21.9 GB size CBS folder of 37 files with a few entries of 2+ GB. Can some files be safely deleted and which ones?
My System SpecsSystem Spec
23 Dec 2015   #9

Windows 7 Ultimate x64

@NoelDP - wanted to follow up on my last post.

It worked! I followed the advice of poster: Gin in the following SuperUser forum: Why is CBS.log file size 20 GB. Don't be alarmed that the thread is in the Windows 8 section, I am using a Windows 7 Ultimate x64 OS.

I disabled the TrustedInstaller.exe in the Services tab of Task Manager. Then I deleted the 100+ GB of data in the C:\windows\logs\cbs directory. Then I enabled TrustedInstaller.exe again, and Windows immediately made a fresh new log.

I guess I will have to continue this process until I can find a permanent fix. In the last 3 weeks, I have a CbsPersist_[x].log file that has grown to 11GB. All scans of my system by my Anti-Virus and by MalwareBytes have come up with no malicious software. I guess it's just Windows acting like Windows :/
My System SpecsSystem Spec
25 Apr 2016   #10

Windows 7

I had 11.0 GB of files here - all the "Persist" logs. I removed all of them. The CBS.log file itself was small, but the others were all 1.0 GB or higher. One of them was even 5.7GB. This is really ridiculous. An average user would never have found these.
My System SpecsSystem Spec

 large size CBS.log files creating, was never before

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