RE: Problems with a C application that changes users and run 'screen-x'
On Dec 20 Paul Everlund wrote: > On Fri, 20 Dec 2002, Paul Everlund wrote: > > Found an error in my reply... > > > On Fri, 20 Dec 2002, Aaron Burke wrote: > > > [big snip] > > > I think execlp is writing over your current process. So first your > > process is exchanged with ppp, then ppp is exchanged with screen. You > > have to make a copy of your current process, a.out, by using fork, and > > then exchange the process image in this copy using execlp. > > Correction... Your a.out process is replaced with ppp, then nothing > else happens, as screen never is called du to the replacement. the process image replaced with "su" and the second execlp() newer called if the first execlp() call succeeds... (which won't) else replaced with "screen" if the second execlp() call succeeds (which won't)... (if exec??() returns, then an error has occured) Here is some code for the OP to start with: #include #include #include #include #include int main(void) { pid_t pid; int s; switch (pid = fork()) { case -1: perror("fork"); exit(EX_OSERR); case 0: /* I'm the child. */ execlp("/usr/bin/su", "/usr/bin/su", "arg1", "arg2", "argn", NULL); /* kaboom */ /* perror("execlp"); */ exit(EX_SOFTWARE); default: /* I'm the parent */ waitpid(pid, &s, 0); break; } return WEXITSTATUS(s); } -andrew To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-questions" in the body of the message
RE: Problems with a C application that changes users and run 'screen-x'
On Fri, 20 Dec 2002, Paul Everlund wrote: Found an error in my reply... > On Fri, 20 Dec 2002, Aaron Burke wrote: > [big snip] > I think execlp is writing over your current process. So first your > process is exchanged with ppp, then ppp is exchanged with screen. You > have to make a copy of your current process, a.out, by using fork, and > then exchange the process image in this copy using execlp. Correction... Your a.out process is replaced with ppp, then nothing else happens, as screen never is called du to the replacement. > Best regards, > Paul Best regards, Paul To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-questions" in the body of the message
RE: Problems with a C application that changes users and run 'screen-x'
On Fri, 20 Dec 2002, Aaron Burke wrote: > > 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 ? > > Allthough I am not familiar with unistd.h at all, I did do > a little bit of expermentation. > > Here is my new code: > > #include > #include > #include > > 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. I think execlp is writing over your current process. So first your process is exchanged with ppp, then ppp is exchanged with screen. You have to make a copy of your current process, a.out, by using fork, and then exchange the process image in this copy using execlp. I suggest you read more about those functions Giorgos mentioned: fork, execlp, waitpid, and exit. Best regards, Paul To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-questions" in the body of the message
RE: Problems with a C application that changes users and run 'screen -x'
> 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 ? Allthough I am not familiar with unistd.h at all, I did do a little bit of expermentation. Here is my new code: #include #include #include 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. To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-questions" in the body of the message
Re: Problems with a C application that changes users and run 'screen -x'
On 2002-12-19 02:50, Aaron Burke <[EMAIL PROTECTED]> wrote: > I have an application that simply logs in as another user and runs > "screen -x". The problem I am having with the followin code is that > the results of execution is a message from (I am guessing the shell) > saying that I dont have access to the "/dev/ttyp?" where ? is the > current virtual terminal that I am running on. > > Here is my application: > > #include > int main(int argc, char* pszArgs[]) > { > int result; > result= system("/usr/bin/su ppp -m --login -c " & > "/usr/local/bin/screen -x"); > return result; > } You are using the & operator in a very strange manner here. It most certainly doesn't work the way you might think it does. You should also avoid using system, if possible. > And here is the output: > bash-2.05$ ./a.out 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: > 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. 2. Fix your program by removing the bad use of `&'. 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. - Giorgos To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-questions" in the body of the message