diff --git a/Makefile b/Makefile
index f0beb51..1c07efd 100644
--- a/Makefile
+++ b/Makefile
@@ -149,6 +149,7 @@ UPROGS=\
 	$U/_grind\
 	$U/_wc\
 	$U/_zombie\
+	$U/_trace\
 
 
 
diff --git a/kernel/proc.c b/kernel/proc.c
index 6afafa1..3de92aa 100644
--- a/kernel/proc.c
+++ b/kernel/proc.c
@@ -274,6 +274,7 @@ fork(void)
     return -1;
   }
   np->sz = p->sz;
+  np->mask = p->mask;
 
   np->parent = p;
 
diff --git a/kernel/proc.h b/kernel/proc.h
index 9c16ea7..872eb38 100644
--- a/kernel/proc.h
+++ b/kernel/proc.h
@@ -93,6 +93,7 @@ struct proc {
   int killed;                  // If non-zero, have been killed
   int xstate;                  // Exit status to be returned to parent's wait
   int pid;                     // Process ID
+  int mask;                    // Tracing mask
 
   // these are private to the process, so p->lock need not be held.
   uint64 kstack;               // Virtual address of kernel stack
diff --git a/kernel/syscall.c b/kernel/syscall.c
index c1b3670..d554c45 100644
--- a/kernel/syscall.c
+++ b/kernel/syscall.c
@@ -104,6 +104,7 @@ extern uint64 sys_unlink(void);
 extern uint64 sys_wait(void);
 extern uint64 sys_write(void);
 extern uint64 sys_uptime(void);
+extern uint64 sys_trace(void);
 
 static uint64 (*syscalls[])(void) = {
 [SYS_fork]    sys_fork,
@@ -127,6 +128,13 @@ static uint64 (*syscalls[])(void) = {
 [SYS_link]    sys_link,
 [SYS_mkdir]   sys_mkdir,
 [SYS_close]   sys_close,
+[SYS_trace]   sys_trace,
+};
+
+static char *syscall_list[23] = {
+  "none",  "fork",  "exit",   "wait",   "pipe",  "read",  "kill",   "exec",
+  "fstat", "chdir", "dup",    "getpid", "sbrk",  "sleep", "uptime", "open",
+  "write", "mknod", "unlink", "link",   "mkdir", "close", "trace"
 };
 
 void
@@ -138,6 +146,9 @@ syscall(void)
   num = p->trapframe->a7;
   if(num > 0 && num < NELEM(syscalls) && syscalls[num]) {
     p->trapframe->a0 = syscalls[num]();
+    if (p->mask & (1 << num))
+      printf("%d: syscall %s -> %d\n", p->pid, syscall_list[num],
+             p->trapframe->a0);
   } else {
     printf("%d %s: unknown sys call %d\n",
             p->pid, p->name, num);
diff --git a/kernel/syscall.h b/kernel/syscall.h
index bc5f356..cc112b9 100644
--- a/kernel/syscall.h
+++ b/kernel/syscall.h
@@ -20,3 +20,4 @@
 #define SYS_link   19
 #define SYS_mkdir  20
 #define SYS_close  21
+#define SYS_trace  22
diff --git a/kernel/sysproc.c b/kernel/sysproc.c
index e8bcda9..8de6712 100644
--- a/kernel/sysproc.c
+++ b/kernel/sysproc.c
@@ -95,3 +95,16 @@ sys_uptime(void)
   release(&tickslock);
   return xticks;
 }
+
+uint64
+sys_trace(void)
+{
+  int mask;
+
+  if (argint(0, &mask) < 0)
+    return -1;
+
+  myproc()->mask = mask;
+
+  return 0;
+}
diff --git a/user/user.h b/user/user.h
index b71ecda..fdeeefc 100644
--- a/user/user.h
+++ b/user/user.h
@@ -23,6 +23,7 @@ int getpid(void);
 char* sbrk(int);
 int sleep(int);
 int uptime(void);
+int trace(int);
 
 // ulib.c
 int stat(const char*, struct stat*);
diff --git a/user/usys.pl b/user/usys.pl
index 01e426e..9c97b05 100755
--- a/user/usys.pl
+++ b/user/usys.pl
@@ -36,3 +36,4 @@ sub entry {
 entry("sbrk");
 entry("sleep");
 entry("uptime");
+entry("trace");