detach.c

   1 #include <stdio.h>
   2 #include <stdlib.h>
   3 #include <sys/types.h>
   4 #include <unistd.h>
   5 #include <fcntl.h>
   6 #include <string.h>
   7
   8 #ifndef NULL
   9 #define NULL  ((void*) 0)
  10 #endif
  11
  12 static void replacefd(int fd, const char *filename, int flags, int mode) {
  13         int n;
  14         n = open(filename, flags, mode);
  15         if(n < 0) {
  16                 perror(filename);
  17                 exit(1);
  18         } else {
  19                 dup2(n, fd);
  20                 close(n);
  21         }
  22 }
  23
  24 int main(int argc, char **argv) {
  25         int do_fork = 1, command_start, i;
  26         char *infile = NULL, *outfile = NULL, *errfile = NULL, *pidfile = NULL;
  27         FILE *pidfh;
  28
  29         /* Parse command line */
  30         for(i = 1; i < argc; i++) {
  31                 if(!strcmp(argv[i], "-e")) errfile = argv[++i];
  32                 else if(!strcmp(argv[i], "-f")) do_fork = 0;
  33                 else if(!strcmp(argv[i], "-i")) infile = argv[++i];
  34                 else if(!strcmp(argv[i], "-o")) outfile = argv[++i];
  35                 else if(!strcmp(argv[i], "-p")) pidfile = argv[++i];
  36                 else if(!strcmp(argv[i], "--")) {
  37                         i++;
  38                         break;
  39                 } else if(argv[i][0] == '-') {
  40                         fprintf(stderr, "Invalid option: %s\n", argv[i]);
  41                         exit(0x80);
  42                 } else break;
  43         }
  44         command_start = i;
  45
  46         if(do_fork && fork()) return 0;
  47
  48         if(pidfile) {
  49                 pidfh = fopen(pidfile, "w");
  50                 if(!pidfh) {
  51                         perror(pidfile);
  52                         exit(1);
  53                 }
  54                 fprintf(pidfh, "%d\n", getpid());
  55                 fclose(pidfh);
  56         }
  57
  58         if(infile) replacefd(0, infile, O_RDONLY, 0666);
  59         else close(0);
  60         if(outfile) replacefd(1, outfile, O_WRONLY | O_CREAT | O_TRUNC, 0666);
  61         else close(1);
  62         if(errfile) replacefd(2, errfile, O_WRONLY | O_CREAT | O_TRUNC, 0666);
  63         else close(2);
  64         setsid();
  65
  66         execvp(argv[command_start], &argv[command_start]);
  67
  68         perror(argv[command_start]);
  69         return -1;
  70 }