Setting primary group in c# on Linux

Question

In Linux, I am logged in as bj:bj as non root user:group.

bj@pc-bj:~$ id
uid=1000(bj) gid=1000(bj) groups=1000(bj),5(tty),20(dialout),24(cdrom),25(floppy),29(audio),1006(internetallowed)

I want to temporary change my primary group to another group "internetallowed" to which I belong. In bash I can do this successfully by the newgrp command:

bj@pc-bj:~$ newgrp internetallowed
bj@pc-bj:~$ id
uid=1000(bj) gid=1006(internetallowed) groups=1006(internetallowed),5(tty),20(dialout),24(cdrom),25(floppy),29(audio),1000(bj)

Now I want to do this also in C# / DotNet 7.0. I've found out that newgrp uses the setgid() function from libc. So I tried this:

public static class LinuxAPI
{
    [DllImport ("libc", SetLastError = true)]
    public static extern int setgid (UInt32 gid);
    public static int GetLastError()
    {
        return Marshal.GetLastSystemError();
    }
}

static void Main(string[] args)
{
    var result = LinuxAPI.setgid(1006);  // returns -1 (error)
    var error = LinuxAPI.GetLastError();  // returns 1 (Operation not permitted)
}

setgid() fails with errno 1 (Operation not permitted). What am I doing wrong?

FSO931s · Accepted Answer · 2023-11-17 21:59:26Z

0

Try replacing

public static int GetLastError()
{
    return Marshal.GetLastSystemError();
}

with

public static int GetLastError()
{
     return Marshal.GetLastWin32Error();
}

answered Nov 17, 2023 at 21:59

FSO931s

1634 silver badges14 bronze badges

Sign up to request clarification or add additional context in comments.

7 Comments

Bigjim Over a year ago

On Linux systems GetLastSystemError() should be used, according to the .net manuals. Even if i use GetLastWin32Error this won't fix the error.

FSO931s Over a year ago

Which version of the .net framework are you using?

Bigjim Over a year ago

using .NET 7.0.403

FSO931s Over a year ago

stackoverflow.com/questions/70479269/… See if this helps any

Bigjim Over a year ago

My issue is not with GetLastError. The function setgid() fails as it returns -1. GetLastError is just to have a clue.

|

Collectives™ on Stack Overflow

Setting primary group in c# on Linux

1 Answer 1

7 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

7 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related