'How to create a process that is not a child of it's creating process?

I have two processes, A and B. At some point A creates B. After B is created, if A's process tree is killed, I want B to still be around.

I am using CreateProcess() to create B, and I can't seem to find any way to make it create the process without it being a child. Same thing with ShellExecuteEx(), but I am probably missing some flag.

Does anyone know what I could use to do this?

EDIT: I forgot to mention that both processes need a HANDLE or process ID to the other

Solution 1:^[1]

You can set the paramaeter dwcreationflags as DETACHED_PROCESS in the createprocess API.

Solution 2:^[2]

When calling kernel32!CreateProcess() you can specify a different parent by using a process attribute. Here is a function that does just that.

bool CreateProcessWithParent(DWORD parentId, PWSTR commandline) {
    auto hProcess = ::OpenProcess(PROCESS_CREATE_PROCESS, FALSE, parentId);
    if (!hProcess)
        return false;
 
    SIZE_T size;
    //
    // call InitializeProcThreadAttributeList twice
    // first, get required size
    //
    ::InitializeProcThreadAttributeList(nullptr, 1, 0, &size);
 
    //
    // now allocate a buffer with the required size and call again
    //
    auto buffer = std::make_unique<BYTE[]>(size);
    auto attributes = reinterpret_cast<PPROC_THREAD_ATTRIBUTE_LIST>(buffer.get());
    ::InitializeProcThreadAttributeList(attributes, 1, 0, &size);
 
    //
    // add the parent attribute
    //
    ::UpdateProcThreadAttribute(attributes, 0, 
        PROC_THREAD_ATTRIBUTE_PARENT_PROCESS, 
        &hProcess, sizeof(hProcess), nullptr, nullptr);
 
    STARTUPINFOEX si = { sizeof(si) };
    //
    // set the attribute list
    //
    si.lpAttributeList = attributes;
    PROCESS_INFORMATION pi;
 
    //
    // create the process
    //
    BOOL created = ::CreateProcess(nullptr, commandline, nullptr, nullptr, 
        FALSE, EXTENDED_STARTUPINFO_PRESENT, nullptr, nullptr, 
        (STARTUPINFO*)&si, &pi);
 
    //
    // cleanup
    //
    ::CloseHandle(hProcess);
    ::DeleteProcThreadAttributeList(attributes);
 
    return created;
}

Source code taken from https://scorpiosoftware.net/2021/01/10/parent-process-vs-creator-process/

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution	Source
Solution 1	Muthukumar Palaniappan
Solution 2

'How to create a process that is not a child of it's creating process?

Solution 1:[1]

Solution 2:[2]

Sources

Related Questions

Solution 1:^[1]

Solution 2:^[2]