The System File Checker

Systems administrators can run the System File Checker (SFC—sfc.exe) utility, which is part of Windows File Protection (WFP), to verify that a system's protected files are valid and to replace problem files. The SFC also reports on files that should be in \winnt\system32\dllcache but aren't. You can run this utility interactively or set it to run at system startup.

Before you use SFC or any other utility, make sure you're running a proper copy of the utility. If you're running a Windows 2000 beta or release candidate (RC) version on your system, I suggest formatting the drive and installing a new copy of Win2K to ensure that you have only one copy of executable files such as sfc.exe.

When you start SFC with the /scannow option, the utility will immediately start a scan and display the WFP status dialog box, which Figure A shows. This dialog displays the system's progress as it scans protected files. You can cancel the process at any time by clicking Cancel on the dialog box. I ran this process on a notebook PC with a 150MHz Pentium processor and 144MB of RAM, and the scan took more than an hour to complete. As the scan progresses, the system repairs files as necessary.

If the scan finds protected files that should be in dllcache but aren't, SFC will prompt you to provide the Win2K CD-ROM, as Figure B shows. If you installed Win2K from a network location that is currently available or the installation CD-ROM is in the drive, you won't see this message because SFC automatically goes to the network location or CD-ROM drive to find the files it needs. When SFC finds the files, it copies them to the dllcache folder, where they will stay in case the system needs a file later.

You can use several options with SFC. The /quiet option causes SFC to perform the scan and replace bad files without user intervention. This option is handy when you need to run SFC in a batch file or from an automated systems management system such as Microsoft Systems Management Server (SMS).

The /scanboot option sets SFC to start at boot time. Each time the system boots, SFC will start and perform the scan. You can use /scanonce to set up SFC to perform only one scan. You can cancel pending scans by using the /cancel option. The /enable option returns WFP to its default operation.

The /cachesize option sets the WFP cache's size. When you run SFC with this option, you specify the size of the cache folder in megabytes. The Microsoft article "Windows File Protection Does Not Reduce Cache Size Automatically" ( kb/articles/q245/8/21.asp) points out that you can reduce cache size only after you reboot and run SFC's /purgecache option to purge the current cache. The documentation also describes how you can use /scannow, /scanonce, and /scanboot to repair a corrupted or damaged dllcache.

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