diff --git a/kernel/buf.h b/kernel/buf.h
index ad2274e..319f8e1 100644
--- a/kernel/buf.h
+++ b/kernel/buf.h
@@ -1,9 +1,3 @@
-#pragma once
-
-#include "types.h"
-#include "sleeplock.h"
-#include "fs.h"
-
 struct buf {
   int              valid; // has data been read from disk?
   int              disk;  // does disk "own" buf?
diff --git a/kernel/defs.h b/kernel/defs.h
index a89c445..b7e0db8 100644
--- a/kernel/defs.h
+++ b/kernel/defs.h
@@ -1,8 +1,3 @@
-#pragma once
-
-#include "riscv.h"
-#include "types.h"
-
 struct buf;
 struct context;
 struct file;
diff --git a/kernel/elf.h b/kernel/elf.h
index acaa17f..a779868 100644
--- a/kernel/elf.h
+++ b/kernel/elf.h
@@ -1,7 +1,3 @@
-#pragma once
-
-#include "types.h"
-
 // Format of an ELF executable file
 
 #define ELF_MAGIC 0x464C457FU // "\x7FELF" in little endian
diff --git a/kernel/fcntl.h b/kernel/fcntl.h
index e19b010..1b57ebb 100644
--- a/kernel/fcntl.h
+++ b/kernel/fcntl.h
@@ -1,5 +1,3 @@
-#pragma once
-
 #define O_RDONLY 0x000
 #define O_WRONLY 0x001
 #define O_RDWR   0x002
diff --git a/kernel/file.h b/kernel/file.h
index d52bbe0..ddb6857 100644
--- a/kernel/file.h
+++ b/kernel/file.h
@@ -1,9 +1,3 @@
-#pragma once
-
-#include "types.h"
-#include "sleeplock.h"
-#include "fs.h"
-
 struct file {
   enum { FD_NONE, FD_PIPE, FD_INODE, FD_DEVICE } type;
   int           ref; // reference count
diff --git a/kernel/fs.h b/kernel/fs.h
index daea0d1..2a6d7bd 100644
--- a/kernel/fs.h
+++ b/kernel/fs.h
@@ -1,7 +1,3 @@
-#pragma once
-
-#include "types.h"
-
 // On-disk file system format.
 // Both the kernel and user programs use this header file.
 
diff --git a/kernel/memlayout.h b/kernel/memlayout.h
index 57c3839..59ff719 100644
--- a/kernel/memlayout.h
+++ b/kernel/memlayout.h
@@ -1,5 +1,3 @@
-#pragma once
-
 // Physical memory layout
 
 // qemu -machine virt is set up like this,
diff --git a/kernel/param.h b/kernel/param.h
index e2dc45a..25643ad 100644
--- a/kernel/param.h
+++ b/kernel/param.h
@@ -1,5 +1,3 @@
-#pragma once
-
 #define NPROC       64                // maximum number of processes
 #define NCPU        8                 // maximum number of CPUs
 #define NOFILE      16                // open files per process
diff --git a/kernel/proc.h b/kernel/proc.h
index d48fd3f..6aed367 100644
--- a/kernel/proc.h
+++ b/kernel/proc.h
@@ -1,10 +1,3 @@
-#pragma once
-
-#include "types.h"
-#include "param.h"
-#include "riscv.h"
-#include "spinlock.h"
-
 // Saved registers for kernel context switches.
 struct context {
   u64 ra;
@@ -111,5 +104,4 @@ struct proc {
   struct file      *ofile[NOFILE]; // Open files
   struct inode     *cwd;           // Current directory
   char              name[16];      // Process name (debugging)
-  int               mask;          // Process mask
 };
diff --git a/kernel/riscv.h b/kernel/riscv.h
index 8fbeadd..21c98cd 100644
--- a/kernel/riscv.h
+++ b/kernel/riscv.h
@@ -1,9 +1,5 @@
-#pragma once
-
 #ifndef __ASSEMBLER__
 
-#include "types.h"
-
 // which hart (core) is this?
 static inline u64
 r_mhartid()
diff --git a/kernel/sleeplock.h b/kernel/sleeplock.h
index b1d0267..7958192 100644
--- a/kernel/sleeplock.h
+++ b/kernel/sleeplock.h
@@ -1,8 +1,3 @@
-#pragma once
-
-#include "types.h"
-#include "spinlock.h"
-
 // Long-term locks for processes
 struct sleeplock {
   u32             locked; // Is the lock held?
diff --git a/kernel/spinlock.h b/kernel/spinlock.h
index dc21dd7..ad6f660 100644
--- a/kernel/spinlock.h
+++ b/kernel/spinlock.h
@@ -1,7 +1,3 @@
-#pragma once
-
-#include "types.h"
-
 // Mutual exclusion lock.
 struct spinlock {
   u32 locked; // Is the lock held?
diff --git a/kernel/stat.h b/kernel/stat.h
index 3b959f9..9bf0083 100644
--- a/kernel/stat.h
+++ b/kernel/stat.h
@@ -1,7 +1,3 @@
-#pragma once
-
-#include "types.h"
-
 #define T_DIR    1 // Directory
 #define T_FILE   2 // File
 #define T_DEVICE 3 // Device
diff --git a/kernel/syscall.c b/kernel/syscall.c
index 075fb36..910b207 100644
--- a/kernel/syscall.c
+++ b/kernel/syscall.c
@@ -101,17 +101,16 @@ extern u64 sys_unlink(void);
 extern u64 sys_link(void);
 extern u64 sys_mkdir(void);
 extern u64 sys_close(void);
-extern u64 sys_trace(void);
 
 // An array mapping syscall numbers from syscall.h
 // to the function that handles the system call.
 static u64 (*syscalls[])(void) = {
-  [SYS_fork] = sys_fork,   [SYS_exit] = sys_exit,     [SYS_wait] = sys_wait,     [SYS_pipe] = sys_pipe,
-  [SYS_read] = sys_read,   [SYS_kill] = sys_kill,     [SYS_exec] = sys_exec,     [SYS_fstat] = sys_fstat,
-  [SYS_chdir] = sys_chdir, [SYS_dup] = sys_dup,       [SYS_getpid] = sys_getpid, [SYS_sbrk] = sys_sbrk,
-  [SYS_sleep] = sys_sleep, [SYS_uptime] = sys_uptime, [SYS_open] = sys_open,     [SYS_write] = sys_write,
-  [SYS_mknod] = sys_mknod, [SYS_unlink] = sys_unlink, [SYS_link] = sys_link,     [SYS_mkdir] = sys_mkdir,
-  [SYS_close] = sys_close, [SYS_trace] = sys_trace,
+  [SYS_fork] sys_fork,   [SYS_exit] sys_exit,     [SYS_wait] sys_wait,     [SYS_pipe] sys_pipe,
+  [SYS_read] sys_read,   [SYS_kill] sys_kill,     [SYS_exec] sys_exec,     [SYS_fstat] sys_fstat,
+  [SYS_chdir] sys_chdir, [SYS_dup] sys_dup,       [SYS_getpid] sys_getpid, [SYS_sbrk] sys_sbrk,
+  [SYS_sleep] sys_sleep, [SYS_uptime] sys_uptime, [SYS_open] sys_open,     [SYS_write] sys_write,
+  [SYS_mknod] sys_mknod, [SYS_unlink] sys_unlink, [SYS_link] sys_link,     [SYS_mkdir] sys_mkdir,
+  [SYS_close] sys_close,
 };
 
 void
diff --git a/kernel/syscall.h b/kernel/syscall.h
index dfc9645..a378a8a 100644
--- a/kernel/syscall.h
+++ b/kernel/syscall.h
@@ -1,5 +1,3 @@
-#pragma once
-
 // System call numbers
 #define SYS_fork   1
 #define SYS_exit   2
@@ -22,4 +20,3 @@
 #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 5645c72..4274a9d 100644
--- a/kernel/sysproc.c
+++ b/kernel/sysproc.c
@@ -89,10 +89,3 @@ sys_uptime(void)
   release(&tickslock);
   return xticks;
 }
-
-u64
-sys_trace(void)
-{
-  /* TODO: Implement sys_trace */
-  return 0;
-}
diff --git a/kernel/types.h b/kernel/types.h
index 03410e3..6626c5e 100644
--- a/kernel/types.h
+++ b/kernel/types.h
@@ -1,5 +1,3 @@
-#pragma once
-
 typedef unsigned char  u8;
 typedef unsigned short u16;
 typedef unsigned int   u32;
diff --git a/kernel/virtio.h b/kernel/virtio.h
index c888436..8916e8a 100644
--- a/kernel/virtio.h
+++ b/kernel/virtio.h
@@ -1,7 +1,4 @@
-#pragma once
-
-#include "types.h"
-
+//
 // virtio device definitions.
 // for both the mmio interface, and virtio descriptors.
 // only tested with qemu.
diff --git a/user/user.h b/user/user.h
index 8b3a1b6..a27f3f1 100644
--- a/user/user.h
+++ b/user/user.h
@@ -1,7 +1,3 @@
-#pragma once
-
-#include "../kernel/types.h"
-
 struct stat;
 
 // system calls
@@ -26,7 +22,6 @@ 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 9c97b05..01e426e 100755
--- a/user/usys.pl
+++ b/user/usys.pl
@@ -36,4 +36,3 @@ entry("getpid");
 entry("sbrk");
 entry("sleep");
 entry("uptime");
-entry("trace");