Date: Fri, 20 Dec 2002 01:13:58 -0800 From: "Aaron Burke" <aburke@nullplusone.com> To: <freebsd-questions@freebsd.org> Subject: RE: Problems with a C application that changes users and run 'screen -x' Message-ID: <NGBBLCIHCLNJAIGIFFHJIEAPCPAA.aburke@nullplusone.com>
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> You're not running the executable as `root'. Since you are not the
> superuser, you do not have permissions to operate on the pseudo-tty
> that login attempts to work with, and this is why you get the
> following error message:
This is as I expected. And I dont know of a way to get around
it.
>
> > Cannot open your terminal '/dev/ttyp0' - please check.
>
> Three possibilities that you might wish to investigate further are:
>
> 1. Write a shell script that does the equivalent of the system() call
> you are using now. This should be fairly easy and will work fine
> if you execute the script from a root shell.
I dont think that this will work. The super-user has nothing to do
with the process that needs to be run. The user that logs in is not
privliged, and the account that he is becomming is not privlidged
either.
>
> 2. Fix your program by removing the bad use of `&'.
Done. Thanks for the comment on this. I noticed a warning from g++ about
this today.
>
> 3. Avoid using system() which I vaguely recall being described with a
> lot of bad words in various places and use fork(), exec(), _exit(),
> waitpid() and exit() instead.
How would I do this with exec. According to the man page for exec
I have only a few options.
int execl(const char *path, const char *arg, ...);
int execlp(const char *file, const char *arg, ...);
int execle(const char *path, const char *arg, ...);
int exect(const char *path, char *const argv[],
char *const envp[]);
int execv(const char *path, char *const argv[]);
int execvp(const char *file, char *const argv[]);
Can you point me to the right documentation to learn about
the exec functions provided by <unistd.h>?
Allthough I am not familiar with unistd.h at all, I did do
a little bit of expermentation.
Here is my new code:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int main(int argc, char* pszArgs[])
{
int result, result2;
result= execlp("/usr/bin/su", "ppp", "-m");
result2=execlp("/usr/local/bin/screen", "-x");
return result + result2;
}
bash-2.05$ g++ run-ppp.c
bash-2.05$ ./a.out
bash-2.05$
I am a little supprised that nothing appeared to have happened.
Perhaps I am running these improperly. Am I using the correct
exec command? Can you demonstrate how this should work?
What else could execlp(args) needs to say?
>
> - Giorgos
>
Thanks for your time.
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