Client/Server Runtime Subsystem

Last updated

The Client/Server Runtime Subsystem, or csrss.exe, is a component of the Windows NT family of operating systems that provides the user mode side of the Win32 subsystem. In modern versions of Windows, it is primarily involved with process and thread management, console window handling, side-by-side assembly loading and the shutdown process. Historically, it had also been responsible for window management and graphics rendering, however, these operations have been moved to kernel mode starting with Windows NT 4.0 to improve performance. [1]

Contents

CSRSS instances are marked as critical processes, meaning that terminating one will crash the system. Built-in process management tools in most Windows versions will also refuse to kill instances of CSRSS. Under normal operation, there is a CSRSS instance for each session (two in Windows Vista and newer, one in earlier versions, [2] both assuming there are no active RDP connections which spawn extra sessions).

Technical details

CSRSS runs as a user-mode system service. When a user-mode process calls a function involving console windows, process/thread creation, or side-by-side support, instead of issuing a system call, the Win32 libraries (kernel32.dll, user32.dll, gdi32.dll) send an inter-process call to the CSRSS process which does most of the actual work without compromising the kernel. [3] Window manager and GDI services are handled by a kernel mode driver (win32k.sys) instead. [4]

CSRSS is called along with winlogon.exe from smss.exe at Windows start-up. If either of the files is corrupted or otherwise inaccessible, SMSS will tell the kernel to shut down the start-up process with a Blue screen of death. [5] The error code for this fault is 0xc000021a (STATUS_SYSTEM_PROCESS_TERMINATED).

In Windows 7 and later, instead of drawing console windows itself, CSRSS spawns conhost.exe subprocesses to draw console windows for command line programs with the permissions of that user.

Malware hoaxes

There are numerous virus hoaxes that claim that csrss.exe is malware and should be removed to prevent damage to the system; these are false, as removing csrss.exe or killing the csrss.exe process will result in a system crash in Windows applications.

In addition, technical support scammers pretending to be Microsoft representatives are known to use csrss.exe as "proof" of a virus infection, and convince the user being scammed into purchasing their rogue security software to remove it. [6]

See also

Related Research Articles

<span class="mw-page-title-main">Windows API</span> Microsofts core set of application programming interfaces on Windows

The Windows API, informally WinAPI, is the foundational application programming interface (API) that allows a computer program to access the features of the Microsoft Windows operating system in which the program is running.

NTLDR is the boot loader for all releases of Windows NT operating system from 1993 with the release of Windows NT 3.1 up until Windows XP and Windows Server 2003. From Windows Vista onwards it was replaced by the BOOTMGR bootloader. NTLDR is typically run from the primary storage device, but it can also run from portable storage devices such as a CD-ROM, USB flash drive, or floppy disk. NTLDR can also load a non NT-based operating system given the appropriate boot sector in a file.

<span class="mw-page-title-main">Windows 9x</span> Series of Microsoft Windows computer operating systems

Windows 9x is a generic term referring to a series of Microsoft Windows computer operating systems produced from 1995 to 2000, which were based on the Windows 95 kernel and its underlying foundation of MS-DOS, both of which were updated in subsequent versions. The first version in the 9x series was Windows 95, which was succeeded by Windows 98 and then Windows Me, which was the third and last version of Windows on the 9x line, until the series was superseded by Windows XP.

<span class="mw-page-title-main">Windows Console</span> Infrastructure for console applications in Microsoft Windows

Windows Console is the infrastructure for console applications in Microsoft Windows. An instance of a Windows Console has a screen buffer and an input buffer. It allows console apps to run inside a window or in hardware text mode. The user can switch between the two using the Alt+↵ Enter key combination. The text mode is unavailable in Windows Vista and later. Starting with Windows 10, however, a native full-screen mode is available.

<span class="mw-page-title-main">Windows Registry</span> Database for Microsoft Windows

The Windows Registry is a hierarchical database that stores low-level settings for the Microsoft Windows operating system and for applications that opt to use the registry. The kernel, device drivers, services, Security Accounts Manager, and user interfaces can all use the registry. The registry also allows access to counters for profiling system performance.

Virtual DOS machines (VDM) refer to a technology that allows running 16-bit/32-bit DOS and 16-bit Windows programs when there is already another operating system running and controlling the hardware.

<span class="mw-page-title-main">Architecture of Windows NT</span> Overview of the architecture of the Microsoft Windows NT line of operating systems

The architecture of Windows NT, a line of operating systems produced and sold by Microsoft, is a layered design that consists of two main components, user mode and kernel mode. It is a preemptive, reentrant multitasking operating system, which has been designed to work with uniprocessor and symmetrical multiprocessor (SMP)-based computers. To process input/output (I/O) requests, it uses packet-driven I/O, which utilizes I/O request packets (IRPs) and asynchronous I/O. Starting with Windows XP, Microsoft began making 64-bit versions of Windows available; before this, there were only 32-bit versions of these operating systems.

<span class="mw-page-title-main">Winlogon</span> Component of Microsoft Windows operating systems

Winlogon is the component of Microsoft Windows operating systems that is responsible for handling the secure attention sequence, loading the user profile on logon, creates the desktops for the window station, and optionally locking the computer when a screensaver is running. In Windows Vista and later operating systems, the roles and responsibilities of Winlogon have changed significantly.

The Local Inter-Process Communication is an internal, undocumented inter-process communication facility provided by the Microsoft Windows NT kernel for lightweight IPC between processes on the same computer. As of Windows Vista, LPC has been rewritten as Asynchronous Local Inter-Process Communication in order to provide a high-speed scalable communication mechanism required to efficiently implement User-Mode Driver Framework (UMDF), whose user-mode parts require an efficient communication channel with UMDF's components in the executive.

The Native API is a lightweight application programming interface (API) used by Windows NT and user mode applications. This API is used in the early stages of Windows NT startup process, when other components and APIs are still unavailable. Therefore, a few Windows components, such as the Client/Server Runtime Subsystem (CSRSS), are implemented using the Native API. The Native API is also used by subroutines such as those in kernel32.dll that implement the Windows API, the API based on which most of the Windows components are created.

ntoskrnl.exe, also known as the kernel image, contains the kernel and executive layers of the Microsoft Windows NT kernel, and is responsible for hardware abstraction, process handling, and memory management. In addition to the kernel and executive layers, it contains the cache manager, security reference monitor, memory manager, scheduler (Dispatcher), and blue screen of death.

A hybrid kernel is an operating system kernel architecture that attempts to combine aspects and benefits of microkernel and monolithic kernel architectures used in operating systems.

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.

The Microsoft Windows operating system supports a form of shared libraries known as "dynamic-link libraries", which are code libraries that can be used by multiple processes while only one copy is loaded into memory. This article provides an overview of the core libraries that are included with every modern Windows installation, on top of which most Windows applications are built.

windows.h is a Windows-specific header file for the C and C++ programming languages which contains declarations for all of the functions in the Windows API, all the common macros used by Windows programmers, and all the data types used by the various functions and subsystems. It defines a very large number of Windows specific functions that can be used in C. The Win32 API can be added to a C programming project by including the <windows.h> header file and linking to the appropriate libraries. To use functions in xxxx.dll, the program must be linked to xxxx.lib. Some headers are not associated with a .dll but with a static library.

The booting process of Microsoft Windows varies between different releases.

Windows Vista has many significant new features compared with previous Microsoft Windows versions, covering most aspects of the operating system.

<span class="mw-page-title-main">Microsoft POSIX subsystem</span> Subsystem shipped with the first versions of Windows NT

Microsoft POSIX subsystem is one of four subsystems shipped with the first versions of Windows NT, the other three being the Win32 subsystem which provided the primary API for Windows NT, plus the OS/2 and security subsystems.

In computing on Microsoft platforms, WoW64 is a subsystem of the Windows operating system capable of running 32-bit applications on 64-bit Windows. It is included in all 64-bit versions of Windows, except in Windows Server Server Core where it is an optional component, and Windows Nano Server where it is not included. WoW64 aims to take care of many of the differences between 32-bit Windows and 64-bit Windows, particularly involving structural changes to Windows itself.

In computing the Process Environment Block is a data structure in the Windows NT operating system family. It is an opaque data structure that is used by the operating system internally, most of whose fields are not intended for use by anything other than the operating system. Microsoft notes, in its MSDN Library documentation — which documents only a few of the fields — that the structure "may be altered in future versions of Windows". The PEB contains data structures that apply across a whole process, including global context, startup parameters, data structures for the program image loader, the program image base address, and synchronization objects used to provide mutual exclusion for process-wide data structures.

References

  1. ↑ "The Windows NT 4.0 Kernel mode change". MS Windows NT Kernel-mode User and GDI White Paper. Microsoft. Retrieved 2009-01-19.
  2. ↑ "Inside the Windows Vista Kernel – Startup Processes". Inside the Windows Vista Kernel – Startup Processes. Microsoft. Retrieved 2010-10-01.
  3. ↑ "Detailed implementation of a system service in Windows NT". Undocumented Windows NT. Archived from the original on 2011-07-17. Retrieved 2010-06-10.
  4. ↑ Russinovich, Mark (2009). Windows Internals, 5th Edition. Microsoft Press. p. 54.
  5. ↑ "How to troubleshoot a "STOP 0xC000021A" error in Windows XP or Windows Server 2003". support.microsoft.com. Retrieved 2020-03-15.
  6. ↑ Cimpanu, Catalin (Jan 22, 2016). "Symantec Disavows Business Partner Caught Running a Tech Support Scam". Softpedia . Retrieved July 29, 2016.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.