diff --git a/lwt/awa_lwt.ml b/lwt/awa_lwt.ml
index 33035b6..a23665f 100644
--- a/lwt/awa_lwt.ml
+++ b/lwt/awa_lwt.ml
@@ -29,23 +29,28 @@ type sshin_msg = [
 ]
 
 type channel = {
-  cmd         : string;
+  cmd         : string option;
   id          : int32;
   sshin_mbox  : sshin_msg Lwt_mvar.t;
   exec_thread : unit Lwt.t;
 }
 
 type exec_callback =
-  string ->                     (* cmd *)
+  ?cmd:string ->                (* cmd *)
   (unit -> sshin_msg Lwt.t) ->  (* sshin *)
   (Cstruct.t -> unit Lwt.t) ->  (* sshout *)
   (Cstruct.t -> unit Lwt.t) ->  (* ssherr *)
   unit Lwt.t
 
+type set_env = string -> string -> unit Lwt.t
+type set_window = term:string -> w:int32 -> h:int32 -> maxw:int32 -> maxh:int32 -> unit Lwt.t
+
 type t = {
   exec_callback  : exec_callback;       (* callback to run on exec *)
   channels       : channel list;        (* Opened channels *)
   nexus_mbox     : nexus_msg Lwt_mvar.t;(* Nexus mailbox *)
+  env            : set_env option;      (* Environment *)
+  window         : set_window option;   (* Window *)
 }
 
 let wrapr = function
@@ -144,6 +149,16 @@ let rec nexus t fd server input_buffer =
        | None -> Lwt.return_unit)
       >>= fun () ->
       nexus t fd server input_buffer
+    | Some Awa.Server.Set_env (k, v) ->
+      ( match t.env with
+      | Some set_env -> set_env k v
+      | None -> Lwt.return_unit ) >>= fun () -> 
+      nexus t fd server input_buffer
+    | Some Awa.Server.Pty (term, w, h, maxw, maxh, _modes) ->
+      ( match t.window with
+      | Some set_window -> set_window ~term ~w ~h ~maxw ~maxh
+      | None -> Lwt.return_unit ) >>= fun () ->
+      nexus t fd server input_buffer
     | Some Awa.Server.Channel_subsystem (id, cmd) (* same as exec *)
     | Some Awa.Server.Channel_exec (id, cmd) ->
       (* Create an input box *)
@@ -153,15 +168,27 @@ let rec nexus t fd server input_buffer =
       let sshout id buf = Lwt_mvar.put t.nexus_mbox (Sshout (id, buf)) in
       let ssherr id buf = Lwt_mvar.put t.nexus_mbox (Ssherr (id, buf)) in
       (* Create the execution thread *)
-      let exec_thread = t.exec_callback cmd sshin (sshout id) (ssherr id) in
-      let c = { cmd; id; sshin_mbox; exec_thread } in
+      let exec_thread = t.exec_callback ~cmd sshin (sshout id) (ssherr id) in
+      let c = { cmd= Some cmd; id; sshin_mbox; exec_thread } in
+      let t = { t with channels = c :: t.channels } in
+      nexus t fd server input_buffer
+    | Some (Awa.Server.Start_shell id) ->
+      (* Create an input box *)
+      let sshin_mbox = Lwt_mvar.create_empty () in
+      (* Create a callback for each mbox *)
+      let sshin () = Lwt_mvar.take sshin_mbox in
+      let sshout id buf = Lwt_mvar.put t.nexus_mbox (Sshout (id, buf)) in
+      let ssherr id buf = Lwt_mvar.put t.nexus_mbox (Ssherr (id, buf)) in
+      (* Create the execution thread *)
+      let exec_thread = t.exec_callback sshin (sshout id) (ssherr id) in
+      let c = { cmd= None; id; sshin_mbox; exec_thread } in
       let t = { t with channels = c :: t.channels } in
       nexus t fd server input_buffer
-    | _ -> nexus t fd server input_buffer
 
-let spawn_server server msgs fd exec_callback =
+let spawn_server ?env ?window server msgs fd exec_callback =
   let t = { exec_callback;
             channels = [];
+            env; window;
             nexus_mbox = Lwt_mvar.create_empty () }
   in
   send_msgs fd server msgs >>= fun server ->
diff --git a/test/awa_lwt_server.ml b/test/awa_lwt_server.ml
index 71da2f9..6a99aac 100644
--- a/test/awa_lwt_server.ml
+++ b/test/awa_lwt_server.ml
@@ -27,21 +27,26 @@ let user_db =
   let awa = Awa.Auth.make_user "awa" [ key ] in
   [ foo; awa ]
 
-let exec addr cmd sshin sshout _ssherror =
+let exec addr ?cmd sshin sshout _ssherror =
   let rec echo () =
     sshin () >>= function
     | `Eof -> Lwt.return_unit
     | `Data input -> sshout input >>= fun () -> echo ()
   in
   let ping () = sshout (Cstruct.of_string "pong\n") in
-  let badcmd () =
+  let badcmd cmd =
     sshout (Cstruct.of_string (Printf.sprintf "Bad command `%s`\n" cmd))
   in
-  Lwt_io.printf "[%s] executing `%s`\n%!" addr cmd >>= fun () ->
-  (match cmd with "echo" -> echo () | "ping" -> ping () | _ -> badcmd ())
-  >>= fun () ->
-  Lwt_io.printf "[%s] execution of `%s` finished\n%!" addr cmd
-  (* XXX Awa_lwt must close the channel when exec returns ! *)
+  match cmd with
+  | None ->
+    Lwt_io.printf "[%s] impossible to execute a shell\n%!" addr >>= fun () ->
+    sshout (Cstruct.of_string (Printf.sprintf "No shell available"))
+  | Some cmd ->
+    Lwt_io.printf "[%s] executing `%s`\n%!" addr cmd >>= fun () ->
+    (match cmd with "echo" -> echo () | "ping" -> ping () | _ -> badcmd cmd)
+    >>= fun () ->
+    Lwt_io.printf "[%s] execution of `%s` finished\n%!" addr cmd
+    (* XXX Awa_lwt must close the channel when exec returns ! *)
 
 let serve rsa fd addr =
   Lwt_io.printf "[%s] connected\n%!" addr >>= fun () ->