xv6

port of xv6 to x86-64
git clone http://frotz.net/git/xv6.git
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init.c (649B)

      1 // init: The initial user-level program
      2 
      3 #include "types.h"
      4 #include "stat.h"
      5 #include "user.h"
      6 #include "fcntl.h"
      7 
      8 char *argv[] = { "sh", 0 };
      9 
     10 int
     11 main(void)
     12 {
     13   int pid, wpid;
     14 
     15   if(open("console", O_RDWR) < 0){
     16     mknod("console", 1, 1);
     17     open("console", O_RDWR);
     18   }
     19   dup(0);  // stdout
     20   dup(0);  // stderr
     21 
     22   for(;;){
     23     printf(1, "init: starting sh\n");
     24     pid = fork();
     25     if(pid < 0){
     26       printf(1, "init: fork failed\n");
     27       exit();
     28     }
     29     if(pid == 0){
     30       exec("sh", argv);
     31       printf(1, "init: exec sh failed\n");
     32       exit();
     33     }
     34     while((wpid=wait()) >= 0 && wpid != pid)
     35       printf(1, "zombie!\n");
     36   }
     37 }