csrss.exe, smss.exe and lsass.exe

Martin Brinkmann
Dec 27, 2007
Updated • Oct 13, 2015
Windows, Windows tips

Whenever I open the Task Manager I see the processes csrss.exe, smss.exe and lsass.exe listed there among others. I guess the same can be said for your version of Windows where those processes are most likely running as well.

To find out if that is the case, use Ctrl-Shift-Esc to bring up the Task Manager. You may need to scroll a bit -- Windows 8 users need to enable the advanced display mode -- before you find the processes, as everything is sorted alphabetically there.

You may also need to select the show processes from all users option before you find them listed here.

So, what are these processes actually doing and are they required to run whenever Windows starts?

Here is the explanation for the three processes csrss.exe, smss.exe and lsass.exe.

smss.exe - Windows Session Manager

The process smss.exe is the Session Manager Subsystem located in C:\Windows\System32. If this file is located somewhere else it is most likely a trojan or virus. It is a critical Windows process that is responsible for the Winlogon and Win32 processes among other things.

To find out if it is located in the right directory, right-click on it and select the open file location option. If it is located in c:\windows\system32, it is in the right location.

The component does a lot of things. It creates environment variables, starts the kernel and user modes of the Win32 subsystem, creates DOS device mappings, virtual memory paging files, and starts winlogon.exe.

csrss.exe - Client Server Runtime Process

csrss.exe client server runtime

Next in the line is the process csrss.exe which is the Windows Client/Server Runtime Server Subsystem. It should be located in C:\Windows\System32 as well. If csrss.exe is located in another location it is most likely a virus or trojan. Like smss.exe csrss.exe is important for Windows to run.

The process is started along with winlogon.exe. If the file is corrupt, Windows will automatically shut down and you will experience a blue screen error with error code 0xc000021a.

The process should not be terminated, as it will lead to system failure if done. If you try to do so under Windows 7 or newer systems, you will receive a warning:

Do you want to end the system process 'csrss.exe'?

Ending this process will shut down the operating system immediately. You will lose all unsaved data. Are you sure you want to continue?


lsass.exe - Local Security Authority Subsystem Service

lsass-exe local security authority process

Last in the line we have lsass.exe which is the Local Security Authentication Server. If lsass.exe is executed from C:\Windows\System32 everything is fine. If it is not it could be a virus or trojan again. All three processes are important Windows system processes and should not be terminated.

This process enforces the security policy on the system. Among other things, it is responsible for user verification, password changes, and the creation of access tokens.

csrss.exe, smss.exe and lsass.exe
Article Name
csrss.exe, smss.exe and lsass.exe
The guide describes what the three system processes csrss.exe, smss.exe and lsass.exe do on Windows.

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  1. Dan Donx said on January 15, 2023 at 10:29 am

    What mental age of reader are you targeting with the first sentence? 10?

    Why not write an article on how to *avoid* upgrading from W10 to W11. Analogous to those like me who avoided upgrading from 7 to 10 for as long as possible.

    If your paymaster Microsoft permits it, of course.

  2. Dexter said on January 15, 2023 at 11:14 am

    5. Rufus
    6. Ventoy

    PS. I hate reading these “SEO optimized” articles.

    1. cdr said on January 15, 2023 at 3:32 pm

      I used Rufus to create an installer for a 6th gen intel i5 that had MBR. It upgraded using Setup. No issues except for Win 11 always prompting me to replace my local account. Still using Win 10 Pro on all my other PCs to avoid the bullying.

  3. sv said on January 15, 2023 at 6:40 pm

    bit pointless to upgrade for the sake of upgrading as you never know when you’ll get locked out because ms might suddenly not provide updates to unsupported systems.

    ps…. time travelling?
    written. Jan 15, 2023
    Updated • Jan 13, 2023

    1. Martin Brinkmann said on January 16, 2023 at 5:49 am

      This happens when you schedule a post in WordPress and update it before setting the publication date.

  4. Anonymous said on January 16, 2023 at 8:24 am

    Anyone willing to downgrade to this awful OS must like inflicting themselves with harm.

  5. basingstoke said on January 16, 2023 at 11:18 am

    I have become convinced now that anybody who has no qualms with using Windows 11/10 must fit into one of the following brackets:

    1) Too young to remember a time before W10 and W11 (doesn’t know better)

    2) Wants to play the latest games on their PC above anything else (or deeply needs some software which already dropped W7 support)

    3) Doesn’t know too much about how computers work, worried that they’d be absolutely lost and in trouble without the “”latest security””

    4) Microsoft apologist that tries to justify that the latest “features” and “changes” are actually a good thing, that improve Windows

    5) Uses their computer to do a bare minimum of like 3 different things, browse web, check emails, etc, so really doesn’t fuss

    Obviously that doesn’t cover everyone, there’s also the category that:

    6) Actually liked W7 more than 10, and held out as long as possible before switching, begrudgingly uses 10 now

    Have I missed any group off this list?

    1. Heinz Strunk said on September 19, 2023 at 3:57 pm

      You have missed in this group just about any professional user that uses business software like CAD programs or ERP Programs which are 99% of all professional users from this list.

      Linux doesn’t help anyone who is not a linux kid and apple is just a fancy facebook machine.

  6. ilev said on August 24, 2023 at 7:34 pm

    Microsoft has removed KB5029351 update

    1. EP said on August 24, 2023 at 9:21 pm

      only from windows update though
      KB5029351 is still available from the ms update catalog site

  7. Anonymous said on August 24, 2023 at 11:05 pm

    1. This update is labaled as PREVIEW if it causes issues to unintelligent people, then they shouldn’t have allowed Preview updates ot install.

    2. I have installed it in a 11 years old computer, and no problems at all.

    3. Making a big drama over a bluescreen for an updated labeled as preview is ridiculous.

    This is probably another BS internet drama where people ran programs and scripts that modified the registry until they broke Windows, just for removing stuff that they weren’t even using just for the sake of it.
    Maybe people should stop playing geeks and actually either use Windows 10 or Windows 11, but don’t try to modify things just for the sake of it.

    Sometimes removing or stopping things (like defender is a perfect example) only need intelligence, not scripts or 3rd party programs that might mess with windows.

  8. john said on August 24, 2023 at 11:17 pm

    Windows 11 was a pointless release, it was just created because some of the Windows team wanted to boost sales with some sort of new and improved Windows 10. Instead, Microsoft cannot support one version well let alone two.

    1. John G. said on August 25, 2023 at 12:08 pm

      Windows 11 is the worst ugly shame by Microsoft ever. They should release with every new W11 version a complete free version of Starallback inside just to make this sh** OS functionally again.

  9. EP said on August 25, 2023 at 3:10 pm

    motherboard maker MSI has recently released a statement regarding the “unsupported processor” blue screen error for their boards using Intel 600/700 series chipsets & to avoid the KB5029351 Win11 update:

  10. EP said on August 29, 2023 at 7:32 pm

    check out the following recent articles:

    Neowin – Microsoft puts little blame on its Windows update after UNSUPPORTED PROCESSOR BSOD bug:

    BleepingComputer – Microsoft blames ‘unsupported processor’ blue screens on OEM vendors:

  11. Leonard Britvolli said on August 30, 2023 at 10:33 pm

    While there may be changes or updates to the Windows 10 Store for Business and Education in the future, it is premature to conclude that it will be discontinued based solely on rumors.

  12. sembrador said on September 5, 2023 at 9:32 pm

    My advice, I left win 15 years ago. Now I’m a happy linux user (linuxmint) but there is Centos, Fedora, Ubuntu depending on your needs.

  13. EP said on September 6, 2023 at 11:55 am

    motherboard maker MSI has recently released new BIOS/firmware updates for their Intel 600 & 700 series motherboards to fix the “UNSUPPORTED_PROCESSOR” problem (Sept. 6):


  14. Raphael Benzo said on September 24, 2023 at 9:52 pm

    I try to disable the Diagnostics Tracking Service (Connected Devices Platform User Services) but it wont let me disable it, any help will be greatly appreciated.
    Tank you for your help

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