Question

When I login in Linux Suse10 machine and check for getlogin_r() through a C++ program, i get a proper result as my login name.

int main()
{
    char szUserName[64] = {0};

    int nGet = getlogin_r(szUserName, sizeof(szUserName)-1);
    if(0 != nGet)
        {
            printerr();
        }
    printf("%s\n", szUserName);
    char * szHome = getlogin();
    printf("%s\n", szHome);
    return 0;
}

But after using the su – name2
i have changed the login now.
But getlogin_r() still shows the older usename.

One solution is the use of geteuid(). But what is the reason of above problem

Answer 1

“after using su - name2 I have changed the login” – No, you haven’t. You’ve changed the user id, not the login.

The man page for su says this about the - option: “Provide an environment similar to what the user would expect had the user logged in directly.” Apparently “similar” is different than “identical to”. Specifically, su - does not store a login record in /var/run/utmp.