Programming

if(fork() == 0) {// childprocess
     chmod(someProgram, 00777);
     exec(someProgram);
} else { // assume it never fails and this is the parent
     chmod(someProgram, 00000); // should be executed as soon as possible after the exec call of the child
}

[john]$ echo 'int main(){printf("hi\n");}' | gcc -x c -o program -
<stdin>: In function ‘main':
<stdin>:1: warning: incompatible implicit declaration of built-in function ‘printf'

[john]$ ls
total 8.0K
-rwxr-xr-x 1 john john 7.0K 2011-04-05 10:47 program*

[john]$ ./program 
hi

[john]$ chmod -x program 

[john]$ ./program
bash: ./program: Permission denied

[john]$ readelf -a program | grep interpreter
      [Requesting program interpreter: /lib/ld-linux.so.2]

[john]$ /lib/ld-linux.so.2 ./program 
hi

[chris@myhost Test]$ ./hw
Hallo welt
[chris@myhost Test]$ ls -l hw
-rwxr-xr-x 1 chris users 5432 Apr  1 14:44 hw
[chris@myhost Test]$ chmod -x hw
[chris@myhost Test]$ ./hw
bash: ./hw: Permission denied
[chris@myhost Test]$ /lib/ld-linux.so.2 ./hw
Hallo welt
[chris@myhost Test]$ chmod -r hw
[chris@myhost Test]$ /lib/ld-linux.so.2 ./hw
./hw: error while loading shared libraries: ./hw: cannot open shared object file: Permission denied
[chris@myhost Test]$ chmod +x hw
[chris@myhost Test]$ ./hw
Hallo welt
[chris@myhost Test]$ /lib/ld-linux.so.2 ./hw
./hw: error while loading shared libraries: ./hw: cannot open shared object file: Permission denied

switch(pid = fork())
{
case -1: perror("fork error");
break;

case 0 : chmod(); //do the process with the file
break;

default :wait(); //wait for the child to finish. claim child's              // resources
             chmod() //change back the permission

break;
}
return 0;
}