Fix dup() -> dup2()

Author: Leedehai

CS110NotesCollection/Topic 2 Multiprocessing (3).md

@@ -194,7 +194,7 @@ subprocess_t subprocess(const char *command) {
 
       /* redirect the child's stdin FD to the pipe's reading end,
          and de-associate fd[0] from the reading end */
-      dup(fds[0], STDIN_FILENO); 
+      dup2(fds[0], STDIN_FILENO); 
       close(fds[0]);
 
       /* now, execute the intended program (/bin/sh) by execvp() */
@@ -216,4 +216,4 @@ subprocess_t subprocess(const char *command) {
 ```
 > Note that if `execvp()` succeeds, then the rest of the code is NOT executed, as the calling process is completely overwritten and rebooted by another program.
 
-###### EOF
+###### EOF