1 #include <sys/types.h>
   2 #include <unistd.h>
   3 #include <stdlib.h>
   4 #include <signal.h>
   5 #include <stdio.h>
   6 #include <errno.h>
   7 #include <string.h>
   8 
   9 int main(int argc, char *argv[])
  10 {
  11     const pid_t parent = getpid();
  12     int timeout;
  13 
  14     if (argc < 3) {
  15         fprintf(stderr, "Usage: %s TIMEOUT COMMAND [ARG]...\n", argv[0]);
  16         return 2;
  17     }
  18     timeout = strtol(argv[1], NULL, 10);
  19     if (timeout <= 0) {
  20         fprintf(stderr, "%s: %s: Invalid argument\n", argv[0], argv[1]);
  21         return 2;
  22     }
  23 
  24     switch (fork()) {
  25         case -1: { // fork failed
  26             fprintf(stderr, "%s: %s\n", argv[0], strerror(errno));
  27             return 126;
  28         }
  29         case 0: { // this is the child, a parricidal watchdog
  30             int seconds;
  31             fclose(stdin);
  32             fclose(stdout);
  33             fclose(stderr);
  34             for (seconds = 0; seconds < timeout; seconds++) {
  35                 sleep(1);
  36                 if (kill(parent, 0) == -1) // has the parent already finished?
  37                     return 0; // okay, there's nothing left to do
  38             }
  39             kill(parent, SIGTERM);
  40             sleep(5);
  41             kill(parent, SIGKILL);
  42             return 0;
  43         }
  44         default: { // this is the parent
  45             execvp(argv[2], &argv[2]);
  46             // upon success, execvp will not return here
  47             if (errno == 2) {
  48                 fprintf(stderr, "%s: %s: Command not found\n", argv[0], argv[2]);
  49                 return 127; // not found
  50             } else {
  51                 fprintf(stderr, "%s: %s: %s\n", argv[0], argv[2], strerror(errno));
  52                 return 126; // not executable
  53             }
  54         }
  55     }
  56 }