diff --git a/defs.h b/defs.h
index 292842834d897b8eca225da6c8703929f43ff8c0..18ff4f150cb83e3476e5ddca8f9667ef47aaf4d5 100644
--- a/defs.h
+++ b/defs.h
@@ -94,6 +94,7 @@ int fd_read(struct fd *fd, char *addr, int n);
 int fd_write(struct fd *fd, char *addr, int n);
 int fd_stat(struct fd *fd, struct stat *);
 void fd_incref(struct fd *fd);
+int fd_dup(struct fd *fd);
 
 // ide.c
 void ide_init(void);
diff --git a/fd.c b/fd.c
index e61cab2f216a8ab8b9ba62e4cb417e63a210c9db..7de4d551447d4ba5c850c49d499c17625bf75bae 100644
--- a/fd.c
+++ b/fd.c
@@ -149,3 +149,9 @@ fd_incref(struct fd *fd)
   fd->ref++;
   release(&fd_table_lock);
 }
+
+int
+fd_dup(struct fd *fd)
+{
+  return -1;
+}
diff --git a/syscall.c b/syscall.c
index 31b61892e543b110c2feca46bdf3a8b69909b2c2..5b857bd7eca5cb3b689d52e79fd31d35d03433e3 100644
--- a/syscall.c
+++ b/syscall.c
@@ -398,6 +398,23 @@ sys_fstat(void)
   return r;
 }
 
+int
+sys_dup(void)
+{
+  struct proc *cp = curproc[cpu()];
+  uint fd;
+  int r;
+  
+  if(fetcharg(0, &fd) < 0)
+    return -1;
+  if(fd < 0 || fd >= NOFILE)
+    return -1;
+  if(cp->fds[fd] == 0)
+    return -1;
+  r = fd_dup (cp->fds[fd]);
+  return r;
+}
+
 int
 sys_link(void)
 {
@@ -543,44 +560,6 @@ sys_exec(void)
   return 0;
 }
 
-int
-sys_block(void)
-{
-  int i, j;
-  struct buf *b;
-  struct inode *ip;
-
-  for (i = 0; i < 2; i++) {
-    cprintf ("issue read\n");
-    b = bread(1, i);
-
-    cprintf("disk 1 sector %d: ", i);
-    for (j = 0; j < 4; j++)
-      cprintf("%x ", b->data[j] & 0xff);
-    cprintf("\n");
-
-    brelse(b);
-  }
-
-  ip = iget(1, 1);
-  cprintf("iget 1: %d %d %d %d %d %d %d %d\n",
-          ip->dev, ip->inum, ip->count, ip->busy,
-          ip->type, ip->nlink, ip->size, ip->addrs[0]);
-  iput(ip);
-
-  ip = namei(".././//./../usertests", NAMEI_LOOKUP, 0);
-  if(ip){
-    cprintf("namei(usertests): %d %d %d %d %d %d %d %d\n",
-            ip->dev, ip->inum, ip->count, ip->busy,
-            ip->type, ip->nlink, ip->size, ip->addrs[0]);
-    iput(ip);
-  } else {
-    cprintf("namei(usertests) failed\n");
-  }
-
-  return 0;
-}
-
 void
 syscall(void)
 {
@@ -610,9 +589,6 @@ syscall(void)
   case SYS_close:
     ret = sys_close();
     break;
-  case SYS_block:
-    ret = sys_block();
-    break;
   case SYS_kill:
     ret = sys_kill();
     break;
@@ -640,6 +616,9 @@ syscall(void)
   case SYS_chdir:
     ret = sys_chdir();
     break;
+  case SYS_dup:
+    ret = sys_dup();
+    break;
   default:
     cprintf("unknown sys call %d\n", num);
     // XXX fault
diff --git a/syscall.h b/syscall.h
index 2209cf24090949748e9fae4bf490a35e03d1f0ce..c89d5a34d5a015a82c5442442272e87d708844ca 100644
--- a/syscall.h
+++ b/syscall.h
@@ -1,18 +1,18 @@
 #define SYS_fork 1
 #define SYS_exit 2
 #define SYS_wait 3
-#define SYS_pipe 5
-#define SYS_write 6
-#define SYS_read 7
-#define SYS_close 8
-#define SYS_block 9
-#define SYS_kill 10
-#define SYS_exec 13
-#define SYS_open 14
-#define SYS_mknod 15
-#define SYS_unlink 16
-#define SYS_fstat 17
-#define SYS_link 18
-#define SYS_mkdir 19
-#define SYS_chdir 20
+#define SYS_pipe 4
+#define SYS_write 5
+#define SYS_read 6
+#define SYS_close 7
+#define SYS_kill 9
+#define SYS_exec 10
+#define SYS_open 11
+#define SYS_mknod 12
+#define SYS_unlink 13
+#define SYS_fstat 14
+#define SYS_link 15
+#define SYS_mkdir 16
+#define SYS_chdir 17
+#define SYS_dup 18
 
diff --git a/user.h b/user.h
index 27f2cfb56b8f58d6d784ed830640da527a0118e5..26d984c95268f291197b446c5076757701c57b93 100644
--- a/user.h
+++ b/user.h
@@ -6,7 +6,6 @@ int pipe(int*);
 int write(int, void*, int);
 int read(int, void*, int);
 int close(int);
-int block(void);
 int kill(int);
 int panic(char*);
 int cons_puts(char*);
@@ -18,6 +17,7 @@ int fstat (int fd, struct stat *stat);
 int link(char *, char *);
 int mkdir(char *);
 int chdir(char *);
+int dup(int);
 
 int stat(char *, struct stat *stat);
 int puts(char*);
diff --git a/userfs.c b/userfs.c
index 5d0c8593c3cf4623c92b651ff2bdbca611de4c3c..25dfaf55950dbcc991f6a66990d4cb94934db385 100644
--- a/userfs.c
+++ b/userfs.c
@@ -20,8 +20,6 @@ main(void)
 
   printf(stdout, "userfs is running\n");
 
-  block();
-
   fd = open("echo", 0);
   if(fd >= 0){
     printf(stdout, "open echo ok\n");
diff --git a/usys.S b/usys.S
index 16d84e74a3a2b63111cb6ac8093e84ca7a9e8e23..c7a162ce6116dcccd63ce7136674aeb8256fe09f 100644
--- a/usys.S
+++ b/usys.S
@@ -15,7 +15,6 @@ STUB(pipe)
 STUB(read)
 STUB(write)
 STUB(close)
-STUB(block)
 STUB(kill)
 STUB(exec)
 STUB(open)
@@ -25,3 +24,4 @@ STUB(fstat)
 STUB(link)
 STUB(mkdir)
 STUB(chdir)
+STUB(dup)