diff --git a/sys/TODO.md b/sys/TODO.md
index fdf188d..7bf787a 100644
--- a/sys/TODO.md
+++ b/sys/TODO.md
@@ -2,8 +2,6 @@
 
 ## Yellowstone
 
-- Add registration to the base yellowstone yunq service
-  - Requires: Adding ability to pass capabilities in endpoint calls.
 - Store registered services in a hashmap.
   - Requires: Adding hashmap to Glacier.
 - Start the next service from a configuration file.
diff --git a/sys/denali/denali.cpp b/sys/denali/denali.cpp
index d4aa72c..2811e6f 100644
--- a/sys/denali/denali.cpp
+++ b/sys/denali/denali.cpp
@@ -29,16 +29,13 @@ uint64_t main(uint64_t init_port_cap) {
   ASSIGN_OR_RETURN(glcr::UniquePtr<EndpointClient> client,
                    server->CreateClient());
 
-  RegisterInfo reg;
-  Empty empty2;
-  check(stub.GetRegister(empty2, reg));
-
-  PortClient register_port = PortClient::AdoptPort(reg.register_port());
-
-  check(register_port.WriteString("denali", client->GetCap()));
-
   Thread server_thread = server->RunServer();
 
+  RegisterEndpointRequest req;
+  req.set_endpoint_name("denali");
+  req.set_endpoint_capability(client->GetCap());
+  check(stub.RegisterEndpoint(req, empty));
+
   check(server_thread.Join());
   return 0;
 }
diff --git a/sys/yellowstone/include/yellowstone/yellowstone.yunq b/sys/yellowstone/include/yellowstone/yellowstone.yunq
index 530c3f1..9c2b134 100644
--- a/sys/yellowstone/include/yellowstone/yellowstone.yunq
+++ b/sys/yellowstone/include/yellowstone/yellowstone.yunq
@@ -1,17 +1,18 @@
 interface Yellowstone {
-  method GetRegister(Empty) -> (RegisterInfo);
+  method RegisterEndpoint(RegisterEndpointRequest) -> (Empty);
   method GetAhciInfo(Empty) -> (AhciInfo);
   method GetDenali(Empty) -> (DenaliInfo);
 }
 
+message RegisterEndpointRequest {
+  string endpoint_name;
+  capability endpoint_capability;
+  }
+
 message Empty {
 
 }
 
-message RegisterInfo {
-  capability register_port;
-}
-
 message AhciInfo {
   capability ahci_region;
   u64 region_length;
diff --git a/sys/yellowstone/include/yellowstone/yellowstone.yunq.client.cpp b/sys/yellowstone/include/yellowstone/yellowstone.yunq.client.cpp
index 2b47570..fa0ec17 100644
--- a/sys/yellowstone/include/yellowstone/yellowstone.yunq.client.cpp
+++ b/sys/yellowstone/include/yellowstone/yellowstone.yunq.client.cpp
@@ -8,7 +8,7 @@
 
 
 
-glcr::ErrorCode YellowstoneClient::GetRegister(const Empty& request, RegisterInfo& response) {
+glcr::ErrorCode YellowstoneClient::RegisterEndpoint(const RegisterEndpointRequest& request, Empty& response) {
   uint64_t buffer_size = kBufferSize;
   uint64_t cap_size = kCapBufferSize;
 
@@ -16,7 +16,7 @@ glcr::ErrorCode YellowstoneClient::GetRegister(const Empty& request, RegisterInf
   buffer_.WriteAt<uint32_t>(0, kSentinel);
   buffer_.WriteAt<uint64_t>(8, 0);
 
-  // FIXME: We need to reset the cap buffer here.
+  cap_buffer_.Reset();
   uint64_t length = request.SerializeToBytes(buffer_, /*offset=*/16, cap_buffer_);
   buffer_.WriteAt<uint32_t>(4, 16 + length);
 
@@ -48,7 +48,7 @@ glcr::ErrorCode YellowstoneClient::GetAhciInfo(const Empty& request, AhciInfo& r
   buffer_.WriteAt<uint32_t>(0, kSentinel);
   buffer_.WriteAt<uint64_t>(8, 1);
 
-  // FIXME: We need to reset the cap buffer here.
+  cap_buffer_.Reset();
   uint64_t length = request.SerializeToBytes(buffer_, /*offset=*/16, cap_buffer_);
   buffer_.WriteAt<uint32_t>(4, 16 + length);
 
@@ -80,7 +80,7 @@ glcr::ErrorCode YellowstoneClient::GetDenali(const Empty& request, DenaliInfo& r
   buffer_.WriteAt<uint32_t>(0, kSentinel);
   buffer_.WriteAt<uint64_t>(8, 2);
 
-  // FIXME: We need to reset the cap buffer here.
+  cap_buffer_.Reset();
   uint64_t length = request.SerializeToBytes(buffer_, /*offset=*/16, cap_buffer_);
   buffer_.WriteAt<uint32_t>(4, 16 + length);
 
diff --git a/sys/yellowstone/include/yellowstone/yellowstone.yunq.client.h b/sys/yellowstone/include/yellowstone/yellowstone.yunq.client.h
index 225b351..56ca541 100644
--- a/sys/yellowstone/include/yellowstone/yellowstone.yunq.client.h
+++ b/sys/yellowstone/include/yellowstone/yellowstone.yunq.client.h
@@ -17,7 +17,7 @@ class YellowstoneClient {
   z_cap_t Capability() { return endpoint_; }
 
 
-  [[nodiscard]] glcr::ErrorCode GetRegister(const Empty& request, RegisterInfo& response);
+  [[nodiscard]] glcr::ErrorCode RegisterEndpoint(const RegisterEndpointRequest& request, Empty& response);
 
   [[nodiscard]] glcr::ErrorCode GetAhciInfo(const Empty& request, AhciInfo& response);
 
diff --git a/sys/yellowstone/include/yellowstone/yellowstone.yunq.cpp b/sys/yellowstone/include/yellowstone/yellowstone.yunq.cpp
index 41dacd1..c2e8e26 100644
--- a/sys/yellowstone/include/yellowstone/yellowstone.yunq.cpp
+++ b/sys/yellowstone/include/yellowstone/yellowstone.yunq.cpp
@@ -27,6 +27,77 @@ void WriteHeader(glcr::ByteBuffer& bytes, uint64_t offset, uint32_t core_size, u
 }
 
 }  // namespace
+void RegisterEndpointRequest::ParseFromBytes(const glcr::ByteBuffer& bytes, uint64_t offset) {
+  CheckHeader(bytes);
+  // Parse endpoint_name.
+  auto endpoint_name_pointer = bytes.At<ExtPointer>(offset + header_size + (8 * 0));
+
+  set_endpoint_name(bytes.StringAt(offset + endpoint_name_pointer.offset, endpoint_name_pointer.length));
+  // Parse endpoint_capability.
+  // FIXME: Implement in-buffer capabilities for inprocess serialization.
+  set_endpoint_capability(0);
+}
+
+void RegisterEndpointRequest::ParseFromBytes(const glcr::ByteBuffer& bytes, uint64_t offset, const glcr::CapBuffer& caps) {
+  CheckHeader(bytes);
+  // Parse endpoint_name.
+  auto endpoint_name_pointer = bytes.At<ExtPointer>(offset + header_size + (8 * 0));
+
+  set_endpoint_name(bytes.StringAt(offset + endpoint_name_pointer.offset, endpoint_name_pointer.length));
+  // Parse endpoint_capability.
+  uint64_t endpoint_capability_ptr = bytes.At<uint64_t>(offset + header_size + (8 * 1));
+
+  set_endpoint_capability(caps.At(endpoint_capability_ptr));
+}
+
+uint64_t RegisterEndpointRequest::SerializeToBytes(glcr::ByteBuffer& bytes, uint64_t offset) const {
+  uint32_t next_extension = header_size + 8 * 2;
+  const uint32_t core_size = next_extension;
+  // Write endpoint_name.
+  ExtPointer endpoint_name_ptr{
+    .offset = next_extension,
+    // FIXME: Check downcast of str length.
+    .length = (uint32_t)endpoint_name().length(),
+  };
+
+  bytes.WriteStringAt(offset + next_extension, endpoint_name());
+  next_extension += endpoint_name_ptr.length;
+
+  bytes.WriteAt<ExtPointer>(offset + header_size + (8 * 0), endpoint_name_ptr);
+  // Write endpoint_capability.
+  // FIXME: Implement inbuffer capabilities.
+  bytes.WriteAt<uint64_t>(offset + header_size + (8 * 1), 0);
+
+  // The next extension pointer is the length of the message. 
+  WriteHeader(bytes, offset, core_size, next_extension);
+
+  return next_extension;
+}
+
+uint64_t RegisterEndpointRequest::SerializeToBytes(glcr::ByteBuffer& bytes, uint64_t offset, glcr::CapBuffer& caps) const {
+  uint32_t next_extension = header_size + 8 * 2;
+  const uint32_t core_size = next_extension;
+  uint64_t next_cap = 0;
+  // Write endpoint_name.
+  ExtPointer endpoint_name_ptr{
+    .offset = next_extension,
+    // FIXME: Check downcast of str length.
+    .length = (uint32_t)endpoint_name().length(),
+  };
+
+  bytes.WriteStringAt(offset + next_extension, endpoint_name());
+  next_extension += endpoint_name_ptr.length;
+
+  bytes.WriteAt<ExtPointer>(offset + header_size + (8 * 0), endpoint_name_ptr);
+  // Write endpoint_capability.
+  caps.WriteAt(next_cap, endpoint_capability());
+  bytes.WriteAt<uint64_t>(offset + header_size + (8 * 1), next_cap++);
+
+  // The next extension pointer is the length of the message. 
+  WriteHeader(bytes, offset, core_size, next_extension);
+
+  return next_extension;
+}
 void Empty::ParseFromBytes(const glcr::ByteBuffer& bytes, uint64_t offset) {
   CheckHeader(bytes);
 }
@@ -55,47 +126,6 @@ uint64_t Empty::SerializeToBytes(glcr::ByteBuffer& bytes, uint64_t offset, glcr:
 
   return next_extension;
 }
-void RegisterInfo::ParseFromBytes(const glcr::ByteBuffer& bytes, uint64_t offset) {
-  CheckHeader(bytes);
-  // Parse register_port.
-  // FIXME: Implement in-buffer capabilities for inprocess serialization.
-  set_register_port(0);
-}
-
-void RegisterInfo::ParseFromBytes(const glcr::ByteBuffer& bytes, uint64_t offset, const glcr::CapBuffer& caps) {
-  CheckHeader(bytes);
-  // Parse register_port.
-  uint64_t register_port_ptr = bytes.At<uint64_t>(offset + header_size + (8 * 0));
-
-  set_register_port(caps.At(register_port_ptr));
-}
-
-uint64_t RegisterInfo::SerializeToBytes(glcr::ByteBuffer& bytes, uint64_t offset) const {
-  uint32_t next_extension = header_size + 8 * 1;
-  const uint32_t core_size = next_extension;
-  // Write register_port.
-  // FIXME: Implement inbuffer capabilities.
-  bytes.WriteAt<uint64_t>(offset + header_size + (8 * 0), 0);
-
-  // The next extension pointer is the length of the message. 
-  WriteHeader(bytes, offset, core_size, next_extension);
-
-  return next_extension;
-}
-
-uint64_t RegisterInfo::SerializeToBytes(glcr::ByteBuffer& bytes, uint64_t offset, glcr::CapBuffer& caps) const {
-  uint32_t next_extension = header_size + 8 * 1;
-  const uint32_t core_size = next_extension;
-  uint64_t next_cap = 0;
-  // Write register_port.
-  caps.WriteAt(next_cap, register_port());
-  bytes.WriteAt<uint64_t>(offset + header_size + (8 * 0), next_cap++);
-
-  // The next extension pointer is the length of the message. 
-  WriteHeader(bytes, offset, core_size, next_extension);
-
-  return next_extension;
-}
 void AhciInfo::ParseFromBytes(const glcr::ByteBuffer& bytes, uint64_t offset) {
   CheckHeader(bytes);
   // Parse ahci_region.
diff --git a/sys/yellowstone/include/yellowstone/yellowstone.yunq.h b/sys/yellowstone/include/yellowstone/yellowstone.yunq.h
index b66b35f..ffea85e 100644
--- a/sys/yellowstone/include/yellowstone/yellowstone.yunq.h
+++ b/sys/yellowstone/include/yellowstone/yellowstone.yunq.h
@@ -5,6 +5,27 @@
 #include <glacier/buffer/cap_buffer.h>
 #include <glacier/string/string.h>
 #include <ztypes.h>
+class RegisterEndpointRequest {
+ public:
+  RegisterEndpointRequest() {}
+  // Delete copy and move until implemented.
+  RegisterEndpointRequest(const RegisterEndpointRequest&) = delete;
+  RegisterEndpointRequest(RegisterEndpointRequest&&) = delete;
+
+  void ParseFromBytes(const glcr::ByteBuffer&, uint64_t offset); 
+  void ParseFromBytes(const glcr::ByteBuffer&, uint64_t offset, const glcr::CapBuffer&);
+  uint64_t SerializeToBytes(glcr::ByteBuffer&, uint64_t offset) const;
+  uint64_t SerializeToBytes(glcr::ByteBuffer&, uint64_t offset, glcr::CapBuffer&) const;
+  glcr::String endpoint_name() const { return endpoint_name_; }
+  void set_endpoint_name(const glcr::String& value) { endpoint_name_ = value; }
+  z_cap_t endpoint_capability() const { return endpoint_capability_; }
+  void set_endpoint_capability(const z_cap_t& value) { endpoint_capability_ = value; }
+
+ private:
+  glcr::String endpoint_name_;
+  z_cap_t endpoint_capability_;
+
+};
 class Empty {
  public:
   Empty() {}
@@ -19,24 +40,6 @@ class Empty {
 
  private:
 
-};
-class RegisterInfo {
- public:
-  RegisterInfo() {}
-  // Delete copy and move until implemented.
-  RegisterInfo(const RegisterInfo&) = delete;
-  RegisterInfo(RegisterInfo&&) = delete;
-
-  void ParseFromBytes(const glcr::ByteBuffer&, uint64_t offset); 
-  void ParseFromBytes(const glcr::ByteBuffer&, uint64_t offset, const glcr::CapBuffer&);
-  uint64_t SerializeToBytes(glcr::ByteBuffer&, uint64_t offset) const;
-  uint64_t SerializeToBytes(glcr::ByteBuffer&, uint64_t offset, glcr::CapBuffer&) const;
-  z_cap_t register_port() const { return register_port_; }
-  void set_register_port(const z_cap_t& value) { register_port_ = value; }
-
- private:
-  z_cap_t register_port_;
-
 };
 class AhciInfo {
  public:
diff --git a/sys/yellowstone/include/yellowstone/yellowstone.yunq.server.cpp b/sys/yellowstone/include/yellowstone/yellowstone.yunq.server.cpp
index ea98ce0..c9660fe 100644
--- a/sys/yellowstone/include/yellowstone/yellowstone.yunq.server.cpp
+++ b/sys/yellowstone/include/yellowstone/yellowstone.yunq.server.cpp
@@ -86,12 +86,12 @@ glcr::ErrorCode YellowstoneServerBase::HandleRequest(const glcr::ByteBuffer& req
 
   switch(method_select) {
     case 0: {
-      Empty yunq_request;
-      RegisterInfo yunq_response;
+      RegisterEndpointRequest yunq_request;
+      Empty yunq_response;
 
       yunq_request.ParseFromBytes(request, kHeaderSize, req_caps);
 
-      RET_ERR(HandleGetRegister(yunq_request, yunq_response));
+      RET_ERR(HandleRegisterEndpoint(yunq_request, yunq_response));
 
       resp_length = yunq_response.SerializeToBytes(response, kHeaderSize, resp_caps);
       break;
diff --git a/sys/yellowstone/include/yellowstone/yellowstone.yunq.server.h b/sys/yellowstone/include/yellowstone/yellowstone.yunq.server.h
index 0d49ef2..13c3da3 100644
--- a/sys/yellowstone/include/yellowstone/yellowstone.yunq.server.h
+++ b/sys/yellowstone/include/yellowstone/yellowstone.yunq.server.h
@@ -21,7 +21,7 @@ class YellowstoneServerBase {
   [[nodiscard]] Thread RunServer();
 
 
-  [[nodiscard]] virtual glcr::ErrorCode HandleGetRegister(const Empty&, RegisterInfo&) = 0;
+  [[nodiscard]] virtual glcr::ErrorCode HandleRegisterEndpoint(const RegisterEndpointRequest&, Empty&) = 0;
 
   [[nodiscard]] virtual glcr::ErrorCode HandleGetAhciInfo(const Empty&, AhciInfo&) = 0;
 
diff --git a/sys/yellowstone/yellowstone.cpp b/sys/yellowstone/yellowstone.cpp
index e367359..5a2f34e 100644
--- a/sys/yellowstone/yellowstone.cpp
+++ b/sys/yellowstone/yellowstone.cpp
@@ -13,7 +13,6 @@ uint64_t main(uint64_t port_cap) {
   check(ParseInitPort(port_cap));
 
   ASSIGN_OR_RETURN(auto server, YellowstoneServer::Create());
-  Thread registration_thread = server->RunRegistration();
   Thread server_thread = server->RunServer();
 
   uint64_t vaddr;
@@ -22,7 +21,6 @@ uint64_t main(uint64_t port_cap) {
   check(SpawnProcessFromElfRegion(vaddr, client.Capability()));
 
   check(server_thread.Join());
-  check(registration_thread.Join());
   dbgln("Yellowstone Finished Successfully.");
   return 0;
 }
diff --git a/sys/yellowstone/yellowstone_server.cpp b/sys/yellowstone/yellowstone_server.cpp
index 133c38e..cfa02a9 100644
--- a/sys/yellowstone/yellowstone_server.cpp
+++ b/sys/yellowstone/yellowstone_server.cpp
@@ -13,11 +13,6 @@
 
 namespace {
 
-void RegistrationThreadBootstrap(void* yellowstone) {
-  dbgln("Yellowstone registration starting");
-  static_cast<YellowstoneServer*>(yellowstone)->RegistrationThread();
-}
-
 struct PartitionInfo {
   uint64_t device_id;
   uint64_t partition_lba;
@@ -38,16 +33,11 @@ glcr::ErrorOr<PartitionInfo> HandleDenaliRegistration(z_cap_t endpoint_cap) {
 glcr::ErrorOr<glcr::UniquePtr<YellowstoneServer>> YellowstoneServer::Create() {
   z_cap_t cap;
   RET_ERR(ZEndpointCreate(&cap));
-  ASSIGN_OR_RETURN(PortServer port, PortServer::Create());
-  return glcr::UniquePtr<YellowstoneServer>(new YellowstoneServer(cap, port));
+  return glcr::UniquePtr<YellowstoneServer>(new YellowstoneServer(cap));
 }
 
-YellowstoneServer::YellowstoneServer(z_cap_t endpoint_cap, PortServer port)
-    : YellowstoneServerBase(endpoint_cap), register_port_(port) {}
-
-Thread YellowstoneServer::RunRegistration() {
-  return Thread(RegistrationThreadBootstrap, this);
-}
+YellowstoneServer::YellowstoneServer(z_cap_t endpoint_cap)
+    : YellowstoneServerBase(endpoint_cap) {}
 
 glcr::ErrorCode YellowstoneServer::HandleGetAhciInfo(const Empty&,
                                                      AhciInfo& info) {
@@ -65,51 +55,30 @@ glcr::ErrorCode YellowstoneServer::HandleGetDenali(const Empty&,
   info.set_lba_offset(lba_offset_);
   return glcr::OK;
 }
-glcr::ErrorCode YellowstoneServer::HandleGetRegister(const Empty&,
-                                                     RegisterInfo& info) {
-  auto client_or = register_port_.CreateClient();
-  if (!client_or.ok()) {
-    dbgln("Error creating register client: %u", client_or.error());
-    return glcr::INTERNAL;
+
+glcr::ErrorCode YellowstoneServer::HandleRegisterEndpoint(
+    const RegisterEndpointRequest& req, Empty&) {
+  dbgln("Registering.");
+  if (req.endpoint_name() == "denali") {
+    denali_cap_ = req.endpoint_capability();
+    auto part_info_or = HandleDenaliRegistration(denali_cap_);
+    if (!part_info_or.ok()) {
+      check(part_info_or.error());
+    }
+    device_id_ = part_info_or.value().device_id;
+    lba_offset_ = part_info_or.value().partition_lba;
+
+    uint64_t vaddr;
+    check(ZAddressSpaceMap(gSelfVmasCap, 0, gBootVictoriaFallsVmmoCap, &vaddr));
+    auto client_or = CreateClient();
+    if (!client_or.ok()) {
+      check(client_or.error());
+    }
+    check(SpawnProcessFromElfRegion(vaddr, client_or.value().Capability()));
+  } else if (req.endpoint_name() == "victoriafalls") {
+    victoria_falls_cap_ = req.endpoint_capability();
+  } else {
+    dbgln("[WARN] Got endpoint cap type: %s", req.endpoint_name().cstr());
   }
-  info.set_register_port(client_or.value().cap());
   return glcr::OK;
 }
-
-void YellowstoneServer::RegistrationThread() {
-  while (true) {
-    uint64_t num_bytes = kBufferSize;
-    z_cap_t endpoint_cap;
-    // FIXME: Better error handling here.
-    check(register_port_.RecvCap(&num_bytes, registration_buffer_,
-                                 &endpoint_cap));
-    glcr::String name(registration_buffer_);
-    if (name == "denali") {
-      denali_cap_ = endpoint_cap;
-      auto part_info_or = HandleDenaliRegistration(denali_cap_);
-      if (!part_info_or.ok()) {
-        check(part_info_or.error());
-      }
-      device_id_ = part_info_or.value().device_id;
-      lba_offset_ = part_info_or.value().partition_lba;
-
-      uint64_t vaddr;
-      check(
-          ZAddressSpaceMap(gSelfVmasCap, 0, gBootVictoriaFallsVmmoCap, &vaddr));
-      auto client_or = CreateClient();
-      if (!client_or.ok()) {
-        check(client_or.error());
-      }
-      check(SpawnProcessFromElfRegion(vaddr, client_or.value().Capability()));
-      continue;
-    }
-
-    if (name == "victoriafalls") {
-      victoria_falls_cap_ = endpoint_cap;
-      continue;
-    }
-
-    dbgln("[WARN] Got endpoint cap type:");
-    dbgln(name.cstr());
-  }
-}
diff --git a/sys/yellowstone/yellowstone_server.h b/sys/yellowstone/yellowstone_server.h
index afe0113..633ab2d 100644
--- a/sys/yellowstone/yellowstone_server.h
+++ b/sys/yellowstone/yellowstone_server.h
@@ -13,22 +13,12 @@ class YellowstoneServer : public YellowstoneServerBase {
  public:
   static glcr::ErrorOr<glcr::UniquePtr<YellowstoneServer>> Create();
 
-  Thread RunRegistration();
-
-  void RegistrationThread();
-
   glcr::ErrorCode HandleGetAhciInfo(const Empty&, AhciInfo&) override;
   glcr::ErrorCode HandleGetDenali(const Empty&, DenaliInfo&) override;
-  glcr::ErrorCode HandleGetRegister(const Empty&, RegisterInfo&) override;
+  glcr::ErrorCode HandleRegisterEndpoint(const RegisterEndpointRequest&,
+                                         Empty&) override;
 
  private:
-  // FIXME: Separate this to its own service.
-  PortServer register_port_;
-
-  static const uint64_t kBufferSize = 128;
-  uint8_t server_buffer_[kBufferSize];
-  char registration_buffer_[kBufferSize];
-
   // TODO: Store these in a data structure.
   z_cap_t denali_cap_ = 0;
   uint64_t device_id_ = 0;
@@ -37,5 +27,5 @@ class YellowstoneServer : public YellowstoneServerBase {
 
   PciReader pci_reader_;
 
-  YellowstoneServer(z_cap_t endpoint_cap, PortServer port);
+  YellowstoneServer(z_cap_t endpoint_cap);
 };
diff --git a/zion/TODO.md b/zion/TODO.md
index ba4a384..6ceda09 100644
--- a/zion/TODO.md
+++ b/zion/TODO.md
@@ -38,6 +38,7 @@
 ## Capabilities
 
 - Add syscalls for inspecting capabilities.
+- Add syscalls for restricting capabilities' permissions.
 - Randomize/obfuscate capability numbers passed to user space.
 - Remove ReplyPort capabilities once the response is sent.