diff --git a/kernel/interrupt/guard.h b/kernel/interrupt/guard.h
index 16c20fc..021b737 100644
--- a/kernel/interrupt/guard.h
+++ b/kernel/interrupt/guard.h
@@ -20,7 +20,9 @@ struct Vault {
 	Bellringer bellringer;
 	BBuffer<Key, 16> keys;
 	Semaphore keys_sem;
+static constexpr int MAX_SEMS =32;
 
+  Semaphore sems[MAX_SEMS];
 	// Ignore this for now, this is for a bonus task
 	Graphics graphics;
 
diff --git a/kernel/sync/semaphore.h b/kernel/sync/semaphore.h
index cb0a9bd..17b3655 100644
--- a/kernel/sync/semaphore.h
+++ b/kernel/sync/semaphore.h
@@ -25,7 +25,6 @@ class Semaphore {
 	// Prevent copies and assignments
 	Semaphore(const Semaphore&) = delete;
 	Semaphore& operator=(const Semaphore&) = delete;
-	unsigned counter;
 	Queue<Thread> waiting;
 
    public:
@@ -33,7 +32,8 @@ class Semaphore {
 	 *  \param c Initial counter value
 	 */
 	explicit Semaphore(unsigned c = 0) : counter(c) {}
-
+	unsigned counter;
+  bool used;
 	/*! \brief Wait for access to the critical area.
 	 *
 	 *  Enter/decrement/wait operation: If the counter is greater than 0, then
diff --git a/kernel/syscall/handler.cc b/kernel/syscall/handler.cc
index fdf609f..f55febb 100644
--- a/kernel/syscall/handler.cc
+++ b/kernel/syscall/handler.cc
@@ -50,7 +50,20 @@ extern "C" size_t syscall_handler(size_t sysnum, size_t p1, size_t p2,
         case Syscall::ID::READ:
             ;
             break;
-    }
+        case Syscall::ID::SEM_INIT:
+            Syscall::Skeleton::sem_init(Guard::enter().vault(), p1, p2);
+            break;
+        case Syscall::ID::SEM_DESTROY:
+            Syscall::Skeleton::sem_destroy(Guard::enter().vault(), p1);
+            break;
+         case Syscall::ID::SEM_WAIT:
+            Syscall::Skeleton::sem_wait(Guard::enter().vault(), p1);
+            break;
+         case Syscall::ID::SEM_SIGNAL:
+            Syscall::Skeleton::sem_signal(Guard::enter().vault(), p1);
+            break;
+ 
+     }
 
 	return static_cast<size_t>(-1);
 }
diff --git a/kernel/syscall/skeleton.cc b/kernel/syscall/skeleton.cc
index 5f7acf8..04694e1 100644
--- a/kernel/syscall/skeleton.cc
+++ b/kernel/syscall/skeleton.cc
@@ -46,25 +46,39 @@ void sleep(Vault &vault, size_t ms) {
 }
 
 bool sem_init(Vault &vault, size_t id, uint32_t value) {
-	(void)vault;
-	(void)id;
-	(void)value;
-	return false;
+  if (id >= vault.MAX_SEMS) {
+    return false;             // out‐of‐range id
+  }
+  if (vault.sems[id].used==1){
+    return false;  //already in use
+  }
+
+  vault.sems[id].counter=value;
+	return true;
 }
 
-void sem_destroy(Vault &vault, size_t id) {
-	(void)vault;
-	(void)id;
+bool sem_destroy(Vault &vault, size_t id) {
+  if (id >= vault.MAX_SEMS) {
+    return false;             // out‐of‐range id
+  }
+  if (vault.sems[id].used==0){
+    return false;  //already in free
+  }
+
+  vault.sems[id].used=0;
+  vault.sems[id].counter=0;
+	return true;
 }
 
-void sem_signal(Vault &vault, size_t id) {
-	(void)vault;
-	(void)id;
+bool sem_signal(Vault &vault, size_t id) {
+  vault.sems[id].v(vault);
+
+  return true;
 }
 
-void sem_wait(Vault &vault, size_t id) {
-	(void)vault;
-	(void)id;
+bool sem_wait(Vault &vault, size_t id) {
+  vault.sems[id].p(vault);
+  return true;
 }
 
 void exit(Vault &vault) { (void)vault; }
diff --git a/kernel/syscall/skeleton.h b/kernel/syscall/skeleton.h
index 5f9f831..7ab0464 100644
--- a/kernel/syscall/skeleton.h
+++ b/kernel/syscall/skeleton.h
@@ -18,9 +18,9 @@ size_t write(Vault &vault, uint32_t id, const void *buffer, size_t size);
 size_t read(Vault &vault, uint32_t id);
 void sleep(Vault &vault, size_t ms);
 bool sem_init(Vault &vault, size_t id, uint32_t value);
-void sem_destroy(Vault &vault, size_t id);
-void sem_signal(Vault &vault, size_t id);
-void sem_wait(Vault &vault, size_t id);
+bool sem_destroy(Vault &vault, size_t id);
+bool sem_signal(Vault &vault, size_t id);
+bool sem_wait(Vault &vault, size_t id);
 void exit(Vault &vault);
 void kill(Vault &vault, size_t pid);
 
diff --git a/kernel/syscall/stub.h b/kernel/syscall/stub.h
index 379ec7d..8661b48 100644
--- a/kernel/syscall/stub.h
+++ b/kernel/syscall/stub.h
@@ -9,6 +9,14 @@ enum class ID : size_t {
 	TEST = 0,
 	WRITE = 1,
 	READ = 2,
+  //SLEEP =3,
+  SEM_INIT=4,
+  SEM_DESTROY=5,
+  SEM_WAIT=6,
+  SEM_SIGNAL=7,
+  //SYS_GETPID=8,
+  //SYS_EXIT= 9,
+  //SYS_KILL=10
 };
 }  // namespace Syscall
 
@@ -26,9 +34,24 @@ extern "C" ssize_t sys_safe_call(Syscall::ID id, size_t p1, size_t p2,
 }
 
 [[gnu::always_inline]] static inline int write(int fd, const void *buf, size_t len, int x = -1, int y = -1) {
-	return sys_call(Syscall::ID::WRITE, fd, (size_t)buf, len, x, y);
+  return sys_call(Syscall::ID::WRITE, fd, (size_t)buf, len, x, y);
 }
 
 [[gnu::always_inline]] static inline int read(int fd, void *buf, size_t len){
 	return sys_call(Syscall::ID::READ, fd, (size_t)buf, len, 0, 0);
 }
+
+[[gnu::always_inline]] static inline int sem_init(int fd, int semid, int value) {
+  return sys_call(Syscall::ID::SEM_INIT, fd, semid, value, 0,0);
+}
+[[gnu::always_inline]] static inline int sem_destroy(int fd, int semid) {
+  return sys_call(Syscall::ID::SEM_DESTROY, fd, semid,0,0,0);
+}
+[[gnu::always_inline]] static inline int sem_wait(int fd, int semid) {
+  return sys_call(Syscall::ID::SEM_WAIT, fd,  semid,0,0,0);
+}
+
+[[gnu::always_inline]] static inline int sem_signal(int fd, int semid) {
+  return sys_call(Syscall::ID::SEM_SIGNAL, fd, semid,0,0,0);
+}
+