detach.c

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