Even when running programs elevated (Administrator), certain registry keys and files are not writable. This may be because the files are owned by TrustedInstaller, and no write access granted for Administrators. In that case, running the program as TrustedInstaller can help fix a locked registry key or clear a file that can’t be accessed anyway.
Note: Running programs under TrustedInstaller privileges can be risky, and you won’t need to do that in most cases, and as long as programs can access the necessary system files. This sort of elevation has to be used only when it’s absolutely necessary and if you know what you’re doing.
I’ve seen cases where TrustedInstaller incorrectly locked down certain system DLLs and the system itself couldn’t read the file, showing 0 KB in Explorer. Accessing the file properties and clicking Security tab said Permissions couldn’t be displayed.
And ICACLS.EXE when run from Admin Command Prompt couldn’t even see the file, as it said "The system cannot find the file specified. Successfully processed 0 files; Failed processing 1 files". The was severely locked down. Eventually I had to use RunAsTi to launch Command Prompt under Ti rights and then clear those files before running the System File Checker.
If you face a similar situation, give PowerRun a shot. PowerRun is a freeware utility that can launch programs under the TrustedInstaller privileges. If you have a locked down registry key or a file owned by TrustedInstaller and can’t rename or replace the file, this tool can help.
Download PowerRun and run it. Open PowerRun.ini and mention the complete path for the program you want to run as TrustedInstaller.
Then double-click PowerRun.exe or PowerRun_x64.exe (for Windows 64 bit) to launch the target application under Ti rights.
Utilities like RunAsTi and PowerRun are powerful — use them only when necessary. Regularly running programs under TrustedInstaller privilege is not recommended.
RunAsTI: Launch processes with TrustedInstaller privilege – Note: Your anti-virus program may warn you when you run RunAsTi. Although the program may be legitimate (with the source code), I presume the virus threat alert may be because the program was misused (to spread malware) by some rogue persons.
About the author
Ramesh Srinivasan founded Winhelponline.com back in 2005. He is passionate about Microsoft technologies and has a vast experience in the ITeS industry — delivering support for Microsoft's consumer products. He has been a Microsoft MVP [2003 to 2012] who contributes to various Windows support forums.