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Session Manager Subsystem

December 07, 2023

The Session Manager Subsystem, or smss.exe, is a component of the Microsoft Windows NT family of operating systems, starting in Windows NT 3.1. It is executed during the startup process of those operating systems.

Session initialization edit

Further information: Booting process of Windows NT § Session manager

The Session Manager Subsystem is the first user-mode process started by the kernel. Once started it creates additional paging files with configuration data from HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management,[1] the environment variables located at the registry entry HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Environment, and DOS device mappings (e.g. CON:, NUL:, AUX:, COM1:, COM2:, COM3:, COM4:, PRN:, LPT1:, LPT2:, LPT3:, and drive letters) listed at the HKLM\System\CurrentControlSet\Control\Session Manager\DOS Devices registry key. This can be used to create permanent subst drives.

The manager is responsible for starting the kernel and user modes of the Win32 subsystem. This subsystem includes win32k.sys (kernel-mode), winsrv.dll (user-mode), and csrss.exe (user-mode).[2] Any other subsystems listed in the Required value of the HKLM\System\CurrentControlSet\Control\Session Manager\SubSystems Registry key are also started.

The manager is also responsible for doing any operations that are requested to be done at the start of a session. Commands listed in HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\BootExecute, such as autochk and convert, are executed. These commands are run before services are loaded by later steps of the booting process.[3] Any rename operations queued at HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\PendingFileRenameOperations. This is used to allow previously in-use files (e.g. drivers) to be replaced as part of a reboot.[4]

Starting with Windows Vista, the Session Manager Subsystem creates a temporary instance of itself that launches the Windows Startup Application (wininit.exe) and a second Client/Server Runtime Subsystem (csrss.exe) for Session 0, a session dedicated to system processes. From here, the Windows Startup Application starts the Service Control Manager (services.exe), which starts all the Windows services that are set to "Auto-Start".[4] The application also starts the Local Security Authority Subsystem Service (lsass.exe). Before Windows Vista, these processes where started by Windows Logon instead of the Windows Startup Application.[5]

Once the session is configured, the Session Manager Subsystem starts Winlogon (Windows Logon Application), which is responsible for handling interactive logons to a Windows system, either local or remote.[5]

Operation edit

After the boot process is finished, the program resides in memory and can be seen running in the Windows Task Manager. It then waits for either winlogon.exe or csrss.exe to end, at which point Windows will shut down. If the processes do not end in an expected fashion, smss.exe may hang the system, or a bugcheck will occur.[6] It also initiates new user sessions when needed.

The Local Session Manager Service (lsm.exe) sends requests to SMSS through the Asynchronous Local Inter-Process Communication (ALPC) port SmSsWinStationApiPort to start new sessions.

Each time a user logs onto the system, the initial Session Manager creates a new instance of itself to configure a new session. This new process starts a Win32 subsystem and Winlogon process for the new session. This allows for multiple users to logon at the same time on Windows Server systems.[5]

See also edit

References edit

  1. ^ "Troubleshooting the Startup Process". Windows XP Resource Kit. Microsoft Technet. November 3, 2005. Retrieved October 24, 2011.
  2. ^ Matt Pietrek (1996). . Microsoft Systems Journal. Archived from the original on November 18, 2012.
  3. ^ "Troubleshooting the Startup Process". Windows XP Resource Kit. Microsoft Technet. November 3, 2005. Retrieved October 24, 2011.
  4. ^ a b Ionescu, Alex; Russinovich, Mark; Solomon, David A. (2012). Windows internals, Part 2 (6th ed.). Redmond, Wash.: Microsoft. pp. 522–527. ISBN 978-0735665873.
  5. ^ a b c Archiveddocs. "Windows Administration: Inside the Windows Vista Kernel: Part 2". learn.microsoft.com. Retrieved 2023-05-13.
  6. ^ Microsoft Corporation (2007). "Default Processes in Windows 2000". Microsoft Corporation. Retrieved 2009-06-14.

Further reading edit

  • Sessions, Desktops and Windows Stations
  • Impact of Session 0 Isolation on Services and Drivers in Windows
  • Session 0 Isolation - Windows 7 - Microsoft

December 07, 2023
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The Session Manager Subsystem or smss exe is a component of the Microsoft Windows NT family of operating systems starting in Windows NT 3 1 It is executed during the startup process of those operating systems Contents 1 Session initialization 2 Operation 3 See also 4 References 5 Further readingSession initialization editFurther information Booting process of Windows NT Session manager The Session Manager Subsystem is the first user mode process started by the kernel Once started it creates additional paging files with configuration data from HKLM SYSTEM CurrentControlSet Control Session Manager Memory Management 1 the environment variables located at the registry entry HKLM SYSTEM CurrentControlSet Control Session Manager Environment and DOS device mappings e g CON NUL AUX COM1 COM2 COM3 COM4 PRN LPT1 LPT2 LPT3 and drive letters listed at the HKLM System CurrentControlSet Control Session Manager DOS Devices registry key This can be used to create permanent subst drives The manager is responsible for starting the kernel and user modes of the Win32 subsystem This subsystem includes win32k sys kernel mode winsrv dll user mode and a href Client Server Runtime Subsystem html title Client Server Runtime Subsystem csrss exe a user mode 2 Any other subsystems listed in the Required value of the HKLM System CurrentControlSet Control Session Manager SubSystems Registry key are also started The manager is also responsible for doing any operations that are requested to be done at the start of a session Commands listed in HKLM SYSTEM CurrentControlSet Control Session Manager BootExecute such as autochk and convert are executed These commands are run before services are loaded by later steps of the booting process 3 Any rename operations queued at HKLM SYSTEM CurrentControlSet Control Session Manager PendingFileRenameOperations This is used to allow previously in use files e g drivers to be replaced as part of a reboot 4 Starting with Windows Vista the Session Manager Subsystem creates a temporary instance of itself that launches the Windows Startup Application wininit exe and a second Client Server Runtime Subsystem csrss exe for Session 0 a session dedicated to system processes From here the Windows Startup Application starts the Service Control Manager services exe which starts all the Windows services that are set to Auto Start 4 The application also starts the Local Security Authority Subsystem Service lsass exe Before Windows Vista these processes where started by Windows Logon instead of the Windows Startup Application 5 Once the session is configured the Session Manager Subsystem starts Winlogon Windows Logon Application which is responsible for handling interactive logons to a Windows system either local or remote 5 Operation editAfter the boot process is finished the program resides in memory and can be seen running in the Windows Task Manager It then waits for either winlogon exe or csrss exe to end at which point Windows will shut down If the processes do not end in an expected fashion smss exe may hang the system or a bugcheck will occur 6 It also initiates new user sessions when needed The Local Session Manager Service lsm exe sends requests to SMSS through the Asynchronous Local Inter Process Communication ALPC port SmSsWinStationApiPort to start new sessions Each time a user logs onto the system the initial Session Manager creates a new instance of itself to configure a new session This new process starts a Win32 subsystem and Winlogon process for the new session This allows for multiple users to logon at the same time on Windows Server systems 5 See also editList of Microsoft Windows components a href Init html title Init init a a similar process in Unix style systemsReferences edit Troubleshooting the Startup Process Windows XP Resource Kit Microsoft Technet November 3 2005 Retrieved October 24 2011 Matt Pietrek 1996 Poking Around Under the Hood A Programmer s View of Windows NT 4 0 Microsoft Systems Journal Archived from the original on November 18 2012 Troubleshooting the Startup Process Windows XP Resource Kit Microsoft Technet November 3 2005 Retrieved October 24 2011 a b Ionescu Alex Russinovich Mark Solomon David A 2012 Windows internals Part 2 6th ed Redmond Wash Microsoft pp 522 527 ISBN 978 0735665873 a b c Archiveddocs Windows Administration Inside the Windows Vista Kernel Part 2 learn microsoft com Retrieved 2023 05 13 Microsoft Corporation 2007 Default Processes in Windows 2000 Microsoft Corporation Retrieved 2009 06 14 Further reading editSessions Desktops and Windows Stations Impact of Session 0 Isolation on Services and Drivers in Windows Session 0 Isolation Windows 7 Microsoft Retrieved from https en wikipedia org w index php title Session Manager Subsystem amp oldid 1164290219, wikipedia, wiki, book, books, library,

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