diff --git a/opam b/opam
index eb6c1a79f..91559e15f 100644
--- a/opam
+++ b/opam
@@ -33,7 +33,7 @@ depends: [
   "result"
   "tar-format" {= "0.6.1"}
   "ipaddr"
-  "lwt" { < "3.0.0" }
+  "lwt" { >= "2.7.0" }
   "uwt" { >= "0.0.4" }
   "tcpip" { >= "2.8.0" & < "3.0.0" }
   "pcap-format"
diff --git a/repo/darwin/packages/local/slirp.local/opam b/repo/darwin/packages/local/slirp.local/opam
index 95c96e461..b8f4febce 100644
--- a/repo/darwin/packages/local/slirp.local/opam
+++ b/repo/darwin/packages/local/slirp.local/opam
@@ -8,7 +8,7 @@ depends: [
   "result"
   "tar-format" {= "0.6.1"}
   "ipaddr"
-  "lwt" { < "3.0.0" }
+  "lwt" { >= "2.7.0" }
   "uwt" {>= "0.0.4"}
   "tcpip" { = "999" }
   "pcap-format"
diff --git a/src/bin/connect.ml b/src/bin/connect.ml
index 1af904e56..8e0c1f507 100644
--- a/src/bin/connect.ml
+++ b/src/bin/connect.ml
@@ -76,7 +76,6 @@ module Make_hvsock(Host: Sig.HOST) = struct
       let flow = F.connect fd in
       Lwt.return { idx; flow }
 
-  let getclientname _ = failwith "Hyper-V socket implementation lacks getsockname"
   let read_into t = F.read_into t.flow
   let read t = F.read t.flow
   let write t = F.write t.flow
diff --git a/src/bin/jbuild b/src/bin/jbuild
index 8c557d71c..b1812870e 100644
--- a/src/bin/jbuild
+++ b/src/bin/jbuild
@@ -5,4 +5,5 @@
      datakit-server.fs9p win-eventlog asl fd-send-recv
    ))
    (preprocess  no_preprocessing)
+   (flags (:standard -warn-error "+1..49-3" -w "A-4-41-42-44"))
 ))
diff --git a/src/bin/main.ml b/src/bin/main.ml
index 1df073341..7a318cf83 100644
--- a/src/bin/main.ml
+++ b/src/bin/main.ml
@@ -19,7 +19,7 @@ module Log = (val Logs.src_log src : Logs.LOG)
 let _ =
   Printexc.register_printer (function
     | Unix.Unix_error(e, _, _) -> Some (Unix.error_message e)
-    | e -> None
+    | _ -> None
   )
 
 let log_exception_continue description f =
@@ -30,8 +30,6 @@ let log_exception_continue description f =
        Lwt.return ()
     )
 
-let default d = function None -> d | Some x -> x
-
 let ethernet_serviceid = "30D48B34-7D27-4B0B-AAAF-BBBED334DD59"
 let ports_serviceid = "0B95756A-9985-48AD-9470-78E060895BE7"
 
@@ -194,7 +192,7 @@ let start_port_forwarding port_control_url max_connections vsock_path =
     );
     Lwt.return_unit
 
-let main_t socket_url port_control_url introspection_url diagnostics_url max_connections vsock_path db_path db_branch dns hosts pcap host_names debug =
+let main_t socket_url port_control_url introspection_url diagnostics_url max_connections vsock_path db_path db_branch dns hosts host_names debug =
   (* Write to stdout if expicitly requested [debug = true] or if the environment
      variable DEBUG is set *)
   let env_debug = try ignore @@ Unix.getenv "DEBUG"; true with Not_found -> false in
@@ -262,17 +260,15 @@ let main_t socket_url port_control_url introspection_url diagnostics_url max_con
   let host_names = List.map Dns.Name.of_string @@ Astring.String.cuts ~sep:"," host_names in
 
   let hardcoded_configuration =
-    let never, _ = Lwt.task () in
-    let pcap = match pcap with None -> None | Some filename -> Some (filename, None) in
     let server_macaddr = Slirp.default_server_macaddr in
     let peer_ip = Ipaddr.V4.of_string_exn "192.168.65.2" in
     let local_ip = Ipaddr.V4.of_string_exn "192.168.65.1" in
     let client_uuids : Slirp.uuid_table = {
-        mutex = Lwt_mutex.create ();
+        Slirp.mutex = Lwt_mutex.create ();
         table = Hashtbl.create 50;
     } in
     let global_arp_table : Slirp.arp_table = {
-        mutex = Lwt_mutex.create ();
+        Slirp.mutex = Lwt_mutex.create ();
         table = [(local_ip, server_macaddr)];
     } in
     {
@@ -353,16 +349,16 @@ let main_t socket_url port_control_url introspection_url diagnostics_url max_con
       | None -> () );
     Lwt.return_unit
 
-let main socket_url port_control_url introspection_url diagnostics_url max_connections vsock_path db_path db_branch dns hosts pcap host_names debug =
+let main socket_url port_control_url introspection_url diagnostics_url max_connections vsock_path db_path db_branch dns hosts host_names debug =
   Host.Main.run
-    (main_t socket_url port_control_url introspection_url diagnostics_url max_connections vsock_path db_path db_branch dns hosts pcap host_names debug)
+    (main_t socket_url port_control_url introspection_url diagnostics_url max_connections vsock_path db_path db_branch dns hosts host_names debug)
 end
 
-let main socket port_control introspection_url diagnostics_url max_connections vsock_path db_path db_branch dns hosts pcap host_names select debug =
+let main socket port_control introspection_url diagnostics_url max_connections vsock_path db_path db_branch dns hosts host_names select debug =
   let module Use_lwt_unix = Main(Host_lwt_unix) in
   let module Use_uwt = Main(Host_uwt) in
   (if select then Use_lwt_unix.main else Use_uwt.main)
-    socket port_control introspection_url diagnostics_url max_connections vsock_path db_path db_branch dns hosts pcap host_names debug
+    socket port_control introspection_url diagnostics_url max_connections vsock_path db_path db_branch dns hosts host_names debug
 
 open Cmdliner
 
@@ -465,13 +461,6 @@ let hosts =
   in
   Arg.(value & opt string Hosts.default_etc_hosts_path doc)
 
-let pcap=
-  let doc =
-    Arg.info ~doc:
-      "Filename to write packet capture data to" ["pcap"]
-  in
-  Arg.(value & opt (some string) None doc)
-
 let host_names =
   let doc =
     Arg.info ~doc:
@@ -495,7 +484,7 @@ let command =
      `P "Terminates TCP/IP and UDP/IP connections from a client and proxy the\
          flows via userspace sockets"]
   in
-  Term.(pure main $ socket $ port_control_path $ introspection_path $ diagnostics_path $ max_connections $ vsock_path $ db_path $ db_branch $ dns $ hosts $ pcap $ host_names $ select $ debug),
+  Term.(pure main $ socket $ port_control_path $ introspection_path $ diagnostics_path $ max_connections $ vsock_path $ db_path $ db_branch $ dns $ hosts  $ host_names $ select $ debug),
   Term.info (Filename.basename Sys.argv.(0)) ~version:Depends.version ~doc ~man
 
 let () =
diff --git a/src/hostnet/capture.ml b/src/hostnet/capture.ml
index 68becd49a..472bf82de 100644
--- a/src/hostnet/capture.ml
+++ b/src/hostnet/capture.ml
@@ -175,7 +175,7 @@ module Make(Input: Sig.VMNET) = struct
   let record t bufs =
     try
       Hashtbl.iter
-        (fun name rule ->
+        (fun _ rule ->
           match Frame.parse bufs with
           | Result.Ok f -> if rule.predicate f then push rule bufs
           | Result.Error (`Msg m) -> failwith m
@@ -232,9 +232,9 @@ module Make(Input: Sig.VMNET) = struct
   let stop_capture _ =
     failwith "Capture.stop_capture unimplemented"
 
-  let get_client_uuid t =
+  let get_client_uuid _ =
     failwith "Capture.get_client_uuid unimplemented"
 
-  let get_client_macaddr t =
+  let get_client_macaddr _ =
     failwith "Capture.get_client_macaddr unimplemented"
 end
diff --git a/src/hostnet/cstructs.ml b/src/hostnet/cstructs.ml
index 0e3b36ab5..7296624c8 100644
--- a/src/hostnet/cstructs.ml
+++ b/src/hostnet/cstructs.ml
@@ -33,7 +33,7 @@ let sub t off len =
   (* trim the length *)
   let rec trim acc ts remaining = match remaining, ts with
     | 0, _ -> List.rev acc
-    | n, [] -> err "invalid bounds in Cstructs.sub %a off=%d len=%d" pp_t t off len
+    | _, [] -> err "invalid bounds in Cstructs.sub %a off=%d len=%d" pp_t t off len
     | n, t :: ts ->
       let to_take = min (Cstruct.len t) n in
       (* either t is consumed and we only need ts, or t has data remaining in which
diff --git a/src/hostnet/dhcp.ml b/src/hostnet/dhcp.ml
index 110c71500..ab85940f2 100644
--- a/src/hostnet/dhcp.ml
+++ b/src/hostnet/dhcp.ml
@@ -30,7 +30,7 @@ module Make(Netif: V1_LWT.NETWORK) = struct
     | hd::tl -> List.fold_left (fun acc x -> if compare acc x > 0 then acc else x) hd tl
 
   (* given some MACs and IPs, construct a usable DHCP configuration *)
-  let make ~client_macaddr ~server_macaddr ~peer_ip ~highest_peer_ip ~local_ip ~extra_dns_ip
+  let make ~server_macaddr ~peer_ip ~highest_peer_ip ~local_ip ~extra_dns_ip
     ~get_domain_search ~get_domain_name netif =
     let open Dhcp_server.Config in
     (* FIXME: We need a DHCP range to make the DHCP server happy, even though we
diff --git a/src/hostnet/dhcp.mli b/src/hostnet/dhcp.mli
index b1bf1fd3e..ccbf604e9 100644
--- a/src/hostnet/dhcp.mli
+++ b/src/hostnet/dhcp.mli
@@ -4,7 +4,7 @@
 module Make(Netif: V1_LWT.NETWORK): sig
   type t
 
-  val make: client_macaddr:Macaddr.t -> server_macaddr:Macaddr.t
+  val make: server_macaddr:Macaddr.t
     -> peer_ip: Ipaddr.V4.t -> highest_peer_ip: Ipaddr.V4.t option -> local_ip:Ipaddr.V4.t
     -> extra_dns_ip:Ipaddr.V4.t list -> get_domain_search:(unit -> string list)
     -> get_domain_name:(unit -> string)
diff --git a/src/hostnet/error.ml b/src/hostnet/error.ml
index 001630b99..231acbbce 100644
--- a/src/hostnet/error.ml
+++ b/src/hostnet/error.ml
@@ -1,14 +1,3 @@
-open Lwt.Infix
-
 type 'a t = ('a, [ `Msg of string ]) Hostnet_lwt_result.t
 
-module FromFlowError(Flow: V1_LWT.FLOW) = struct
-  let (>>=) m f = m >>= function
-    | `Eof -> Lwt.return (Result.Error (`Msg "Unexpected end of file"))
-    | `Error e -> Lwt.return (Result.Error (`Msg (Flow.error_message e)))
-    | `Ok x -> f x
-end
-
-let errorf fmt = Printf.ksprintf (fun s -> Lwt.return (Result.Error (`Msg s))) fmt
-
 module Infix = Hostnet_lwt_result.Infix
diff --git a/src/hostnet/filter.ml b/src/hostnet/filter.ml
index dc8868f1e..739b4c9f1 100644
--- a/src/hostnet/filter.ml
+++ b/src/hostnet/filter.ml
@@ -107,10 +107,10 @@ module Make(Input: Sig.VMNET) = struct
   let of_fd ~client_macaddr_of_uuid:_ ~server_macaddr:_ ~mtu:_ =
     failwith "Filter.of_fd unimplemented"
 
-  let get_client_uuid t =
+  let get_client_uuid _ =
     failwith "Filter.get_client_uuid unimplemented"
 
-  let get_client_macaddr t =
+  let get_client_macaddr _ =
     failwith "Filter.get_client_macaddr unimplemented"
 
   let start_capture _ ?size_limit:_ _ =
diff --git a/src/hostnet/forward.ml b/src/hostnet/forward.ml
index 5dd5a0307..79f2b6994 100644
--- a/src/hostnet/forward.ml
+++ b/src/hostnet/forward.ml
@@ -31,26 +31,14 @@ module Result = struct
 end
 
 module Int16 = struct
-  module M = struct
-    type t = int
-    let compare (a: t) (b: t) = Pervasives.compare a b
-  end
-  include M
-  module Map = Map.Make(M)
-  module Set = Set.Make(M)
+  type t = int
 end
 
 module Port = struct
-  module M = struct
-    type t = [
-      | `Tcp of Ipaddr.t * Int16.t
-      | `Udp of Ipaddr.t * Int16.t
-    ]
-    let compare = compare
-  end
-  include M
-  module Map = Map.Make(M)
-  module Set = Set.Make(M)
+  type t = [
+    | `Tcp of Ipaddr.t * Int16.t
+    | `Udp of Ipaddr.t * Int16.t
+  ]
 
   let to_string = function
     | `Tcp (addr, port) -> Printf.sprintf "tcp:%s:%d" (Ipaddr.to_string addr) port
@@ -85,8 +73,6 @@ type key = Port.t
 
 let get_key t = t.local
 
-module Map = Port.Map
-
 type context = string
 
 let to_string t = Printf.sprintf "%s:%s" (Port.to_string t.local) (Port.to_string t.remote_port)
diff --git a/src/hostnet/host_lwt_unix.ml b/src/hostnet/host_lwt_unix.ml
index 5941f229b..89126f530 100644
--- a/src/hostnet/host_lwt_unix.ml
+++ b/src/hostnet/host_lwt_unix.ml
@@ -37,7 +37,7 @@ exception Too_many_connections
 let connection_table = Hashtbl.create 511
 let connections () =
   let xs = Hashtbl.fold (fun _ c acc -> c :: acc) connection_table [] in
-  Vfs.File.ro_of_string @@ String.concat "\n" xs
+  Vfs.File.ro_of_string (String.concat "\n" xs)
 let register_connection_no_limit description =
   let idx = next_connection_idx () in
   Hashtbl.replace connection_table idx description;
@@ -87,7 +87,8 @@ let unix_bind_one ?(description="") pf ty ip port =
   Lwt.catch
     (fun () ->
       Lwt_unix.setsockopt fd Lwt_unix.SO_REUSEADDR true;
-      Lwt_unix.bind fd addr;
+      Lwt_unix.Versioned.bind_2 fd addr
+      >>= fun () ->
       Lwt.return (idx, fd)
     ) (fun e ->
       Lwt_unix.close fd
@@ -168,7 +169,8 @@ module Datagram = struct
         | Ipaddr.V6 _ -> Lwt_unix.PF_INET6, Unix.inet6_addr_any in
       let fd = Lwt_unix.socket pf Lwt_unix.SOCK_DGRAM 0 in
       (* Win32 requires all sockets to be bound however macOS and Linux don't *)
-      (try Lwt_unix.bind fd (Lwt_unix.ADDR_INET(addr, 0)) with _ -> ());
+      Lwt.catch (fun () -> Lwt_unix.Versioned.bind_2 fd (Lwt_unix.ADDR_INET(addr, 0))) (fun _ -> Lwt.return_unit)
+      >>= fun () ->
       let sockaddr = sockaddr_of_address address in
       Lwt.return (Result.Ok (of_fd ~idx ~description ?read_buffer_size sockaddr address fd))
 
@@ -629,7 +631,8 @@ module Stream = struct
         let s = Lwt_unix.socket Lwt_unix.PF_UNIX Lwt_unix.SOCK_STREAM 0 in
         Lwt.catch
           (fun () ->
-            Lwt_unix.bind s (Lwt_unix.ADDR_UNIX path);
+            Lwt_unix.Versioned.bind_2 s (Lwt_unix.ADDR_UNIX path)
+            >>= fun () ->
             Lwt.return (make ~path [ idx, s ])
           ) (fun e ->
             Lwt_unix.close s
diff --git a/src/hostnet/host_uwt.ml b/src/hostnet/host_uwt.ml
index b31b1838a..6937baf0a 100644
--- a/src/hostnet/host_uwt.ml
+++ b/src/hostnet/host_uwt.ml
@@ -71,7 +71,7 @@ module Sockets = struct
   let connection_table = Hashtbl.create 511
   let connections () =
     let xs = Hashtbl.fold (fun _ c acc -> c :: acc) connection_table [] in
-    Vfs.File.ro_of_string @@ String.concat "\n" xs
+    Vfs.File.ro_of_string (String.concat "\n" xs)
   let register_connection_no_limit description =
     let idx = next_connection_idx () in
     Hashtbl.replace connection_table idx description;
diff --git a/src/hostnet/hostnet_dns.ml b/src/hostnet/hostnet_dns.ml
index daed52b9c..8dc86a7d2 100644
--- a/src/hostnet/hostnet_dns.ml
+++ b/src/hostnet/hostnet_dns.ml
@@ -31,7 +31,7 @@ module Policy(Files: Sig.FILES) = struct
   let config_of_ips ips =
     let open Dns_forward.Config in
     let servers = Server.Set.of_list (
-      List.map (fun (ip, port) ->
+      List.map (fun (ip, _) ->
         { Server.address = { Address.ip; port = 53 }; zones = Domain.Set.empty;
         timeout_ms = Some 2000; order = 0 }
       ) ips) in
@@ -162,11 +162,11 @@ module Make(Ip: V1_LWT.IPV4) (Udp:V1_LWT.UDPV4) (Tcp:V1_LWT.TCPV4) (Socket: Sig.
   let set_recorder r = recorder := Some r
 
   let destroy = function
-    | { resolver = Upstream { dns_tcp_resolver; dns_udp_resolver } } ->
+    | { resolver = Upstream { dns_tcp_resolver; dns_udp_resolver; _ }; _ } ->
       Dns_tcp_resolver.destroy dns_tcp_resolver
       >>= fun () ->
       Dns_udp_resolver.destroy dns_udp_resolver
-    | { resolver = Host } ->
+    | { resolver = Host; _ } ->
       Lwt.return_unit
 
   let record_udp ~source_ip ~source_port ~dest_ip ~dest_port bufs =
@@ -212,12 +212,6 @@ module Make(Ip: V1_LWT.IPV4) (Udp:V1_LWT.UDPV4) (Tcp:V1_LWT.TCPV4) (Socket: Sig.
     | None ->
       () (* nowhere to log packet *)
 
-  let try_host_resolver question =
-    D.resolve question
-    >>= function
-    | [] -> Lwt.return None
-    | x -> Lwt.return (Some x)
-
   let create ~local_address ~host_names =
     let local_ip = local_address.Dns_forward.Config.Address.ip in
     Log.info (fun f -> f "DNS names %s will map to local IP %s" (String.concat ", " @@ List.map Dns.Name.to_string host_names) (Ipaddr.to_string local_ip));
@@ -247,6 +241,7 @@ module Make(Ip: V1_LWT.IPV4) (Udp:V1_LWT.UDPV4) (Tcp:V1_LWT.TCPV4) (Socket: Sig.
       Lwt.return { local_ip; host_names; resolver = Host }
 
   let answer t is_tcp buffer =
+    let open Dns.Packet in
     let len = Cstruct.len buffer in
     let buf = Dns.Buf.of_cstruct buffer in
     match Dns.Protocol.Server.parse (Dns.Buf.sub buf 0 len) with
@@ -303,7 +298,7 @@ module Make(Ip: V1_LWT.IPV4) (Udp:V1_LWT.UDPV4) (Tcp:V1_LWT.TCPV4) (Socket: Sig.
     | None -> Printf.sprintf "Unparsable DNS packet length %d" len
     | Some request -> Dns.Packet.to_string request
 
-  let handle_udp ~t ~udp ~src ~dst ~src_port buf =
+  let handle_udp ~t ~udp ~src ~dst:_ ~src_port buf =
     answer t false buf
     >>= function
     | Result.Error (`Msg m) ->
@@ -314,7 +309,7 @@ module Make(Ip: V1_LWT.IPV4) (Udp:V1_LWT.UDPV4) (Tcp:V1_LWT.TCPV4) (Socket: Sig.
 
   let handle_tcp ~t =
     (* FIXME: need to record the upstream request *)
-    let listeners port =
+    let listeners _ =
       Log.debug (fun f -> f "DNS TCP handshake complete");
       Some (fun flow ->
         let packets = Dns_tcp_framing.connect flow in
diff --git a/src/hostnet/hosts.ml b/src/hostnet/hosts.ml
index fb681c930..7425a90ee 100644
--- a/src/hostnet/hosts.ml
+++ b/src/hostnet/hosts.ml
@@ -24,7 +24,7 @@ let of_string txt =
         if line = "" then acc else begin
           let line = match String.cut ~sep:"#" line with
             | None -> line
-            | Some (important, comment) -> important in
+            | Some (important, _) -> important in
           let whitespace = function
             | ' ' | '\n' | '\011' | '\012' | '\r' | '\t' -> true
             | _ -> false in
diff --git a/src/hostnet/jbuild b/src/hostnet/jbuild
index 583d0391d..448e93190 100644
--- a/src/hostnet/jbuild
+++ b/src/hostnet/jbuild
@@ -11,4 +11,5 @@
    ))
    (c_names (stubs_utils))
    (wrapped false)
+   (flags (:standard -warn-error "+1..49-3" -w "A-4-41-42-44"))
 ))
diff --git a/src/hostnet/mux.ml b/src/hostnet/mux.ml
index 4b71594eb..678ebc341 100644
--- a/src/hostnet/mux.ml
+++ b/src/hostnet/mux.ml
@@ -67,7 +67,7 @@ module Make(Netif: V1_LWT.NETWORK) = struct
         (fun ip t acc ->
           Printf.sprintf "%s last_active_time = %.1f" (Ipaddr.V4.to_string ip) t.last_active_time :: acc
         ) t.rules [] in
-    Vfs.File.ro_of_string @@ String.concat "\n" xs
+    Vfs.File.ro_of_string (String.concat "\n" xs)
 
   let remove t rule =
     Log.debug (fun f -> f "removing switch port for %s" (Ipaddr.V4.to_string rule));
@@ -77,7 +77,7 @@ module Make(Netif: V1_LWT.NETWORK) = struct
     (* Does the packet match any of our rules? *)
     let open Frame in
     match parse [ buf ] with
-    | Ok (Ethernet { payload = Ipv4 { dst } }) ->
+    | Ok (Ethernet { payload = Ipv4 { dst; _ }; _ }) ->
       if RuleMap.mem dst t.rules then begin
         let port = RuleMap.find dst t.rules in
         port.last_active_time <- Unix.gettimeofday ();
diff --git a/src/hostnet/slirp.ml b/src/hostnet/slirp.ml
index 6eb61dafc..eb6ea3194 100644
--- a/src/hostnet/slirp.ml
+++ b/src/hostnet/slirp.ml
@@ -196,7 +196,7 @@ module Make(Config: Active_config.S)(Vmnet: Sig.VMNET)(Dns_policy: Sig.DNS_POLIC
 
       let filesystem () =
         let flows = Id.Map.fold (fun _ t acc -> to_string t :: acc) !all [] in
-        Vfs.File.ro_of_string @@ String.concat "\n" flows
+        Vfs.File.ro_of_string (String.concat "\n" flows)
 
       let create id socket =
         let socket = Some socket in
@@ -526,7 +526,7 @@ module Make(Config: Active_config.S)(Vmnet: Sig.VMNET)(Dns_policy: Sig.DNS_POLIC
           (fun ip t acc ->
              Printf.sprintf "%s last_active_time = %.1f" (Ipaddr.V4.to_string ip) t.Endpoint.last_active_time :: acc
           ) t.endpoints [] in
-      Vfs.File.ro_of_string @@ String.concat "\n" xs in
+      Vfs.File.ro_of_string (String.concat "\n" xs) in
     Vfs.Dir.of_list
       (fun () ->
          Vfs.ok [
@@ -669,7 +669,7 @@ module Make(Config: Active_config.S)(Vmnet: Sig.VMNET)(Dns_policy: Sig.DNS_POLIC
             None (* just set smallest available prefix *)
         end
     in
-    let dhcp = Dhcp.make ~client_macaddr ~server_macaddr ~peer_ip ~highest_peer_ip ~local_ip
+    let dhcp = Dhcp.make ~server_macaddr ~peer_ip ~highest_peer_ip ~local_ip
       ~extra_dns_ip ~get_domain_search ~get_domain_name switch in
 
     let endpoints = IPMap.empty in
@@ -741,7 +741,7 @@ module Make(Config: Active_config.S)(Vmnet: Sig.VMNET)(Dns_policy: Sig.DNS_POLIC
       (fun buf ->
          let open Frame in
          match parse [ buf ] with
-         | Ok (Ethernet { src = eth_src ; dst = eth_dst ; payload }) when
+         | Ok (Ethernet { src = eth_src ; dst = eth_dst ; _ }) when
             (not (Macaddr.compare eth_dst client_macaddr = 0 ||
                   Macaddr.compare eth_dst server_macaddr = 0 ||
                   Macaddr.compare eth_dst Macaddr.broadcast = 0)) -> (* not to server, client or broadcast.. *)
@@ -1048,7 +1048,7 @@ module Make(Config: Active_config.S)(Vmnet: Sig.VMNET)(Dns_policy: Sig.DNS_POLIC
             let client_macaddr = (Vnet.mac l2_switch l2_client_id) in
 
             let used_ips =
-                Hashtbl.fold (fun k v l ->
+                Hashtbl.fold (fun _ v l ->
                     let ip, _ = v in
                     l @ [ip]) t.client_uuids.table []
             in
@@ -1072,7 +1072,7 @@ module Make(Config: Active_config.S)(Vmnet: Sig.VMNET)(Dns_policy: Sig.DNS_POLIC
                     if not (List.mem preferred_ip used_ips) then begin
                         Some preferred_ip
                     end else begin
-                        failwith "Preferred IP address %s not available" (Ipaddr.V4.to_string preferred_ip)
+                        failwith (Printf.sprintf "Preferred IP address %s not available" (Ipaddr.V4.to_string preferred_ip))
                     end
                 end else begin
                     None
diff --git a/src/hostnet/vmnet.ml b/src/hostnet/vmnet.ml
index 6096da2ab..6e03fac0c 100644
--- a/src/hostnet/vmnet.ml
+++ b/src/hostnet/vmnet.ml
@@ -1,7 +1,6 @@
 module Lwt_result = Hostnet_lwt_result (* remove when new Lwt is released *)
 
 open Lwt
-open Sexplib.Std
 
 let src =
   let src = Logs.Src.create "vmnet" ~doc:"vmnet" in
@@ -10,14 +9,6 @@ let src =
 
 module Log = (val Logs.src_log src : Logs.LOG)
 
-let log_exception_continue description f =
-  Lwt.catch
-    (fun () -> f ())
-    (fun e ->
-       Log.err (fun f -> f "%s: caught %s" description (Printexc.to_string e));
-       Lwt.return ()
-    )
-
 let ethernet_header_length = 14 (* no VLAN *)
 
 module Init = struct
@@ -215,10 +206,10 @@ let server_negotiate ~fd ~client_macaddr_of_uuid ~mtu =
       >>= fun (command, _) ->
       Log.info (fun f -> f "PPP.negotiate: received %s" (Command.to_string command));
       match command with
-      | Ethernet uuid -> begin
+      | Command.Ethernet uuid -> begin
           let open Lwt.Infix in
           client_macaddr_of_uuid uuid
-          >>= fun client_macaddr -> 
+          >>= fun client_macaddr ->
           let vif = Vif.create client_macaddr mtu () in
           let buf = Cstruct.create Vif.sizeof in
           let (_: Cstruct.t) = Vif.marshal vif buf in
@@ -229,7 +220,7 @@ let server_negotiate ~fd ~client_macaddr_of_uuid ~mtu =
           >>= fun () ->
           Lwt_result.return (uuid, client_macaddr)
         end
-      | Bind_ipv4 _ -> (raise (Failure "PPP.negotiate: unsupported command Bind_ipv4"))
+      | Command.Bind_ipv4 _ -> (raise (Failure "PPP.negotiate: unsupported command Bind_ipv4"))
     )
 
 let client_negotiate ~uuid ~fd =
@@ -341,9 +332,9 @@ let of_fd ~client_macaddr_of_uuid ~server_macaddr ~mtu flow =
 let client_of_fd ~uuid ~server_macaddr flow =
   let open Lwt_result.Infix in
   let channel = Channel.create flow in
-  client_negotiate ~uuid ~fd:channel 
+  client_negotiate ~uuid ~fd:channel
   >>= fun vif ->
-  let t = make vif.client_macaddr server_macaddr vif.mtu uuid channel in
+  let t = make ~client_macaddr:vif.Vif.client_macaddr ~server_macaddr:server_macaddr ~mtu:vif.Vif.mtu ~client_uuid:uuid channel in
   Lwt_result.return t
 
 let disconnect t = match t.fd with
@@ -540,5 +531,4 @@ let reset_stats_counters t =
   t.stats.rx_pkts <- 0l;
   t.stats.tx_pkts <- 0l
 
-let get_id _ = ()
 end
diff --git a/src/hostnet_test/forwarding.ml b/src/hostnet_test/forwarding.ml
index e84bdeaee..93ac20196 100644
--- a/src/hostnet_test/forwarding.ml
+++ b/src/hostnet_test/forwarding.ml
@@ -67,8 +67,6 @@ module ForwardServer = struct
 end
 
 module Forward = Forward.Make(struct
-  type port = Forward.Port.t
-
   include Host.Sockets.Stream.Tcp
 
   open Lwt.Infix
@@ -226,7 +224,7 @@ module ForwardControl = struct
         Lwt.return { t; fid; ip; port }
       | _ -> failwith ("failed to parse response: " ^ line)
     end else failwith response
-  let destroy { t; fid } =
+  let destroy { t; fid; _ } =
     Client.LowLevel.clunk t.ninep fid
     >>*= fun _clunk ->
     Lwt.return ()
diff --git a/src/hostnet_test/jbuild b/src/hostnet_test/jbuild
index ec5f5813e..201d5b7b2 100644
--- a/src/hostnet_test/jbuild
+++ b/src/hostnet_test/jbuild
@@ -5,4 +5,5 @@
      dns.mirage lwt.preemptive uwt.preemptive
    ))
    (preprocess  no_preprocessing)
+   (flags (:standard -warn-error "+1..49-3" -w "A-4-41-42-44"))
 ))
diff --git a/src/hostnet_test/main_lwt.ml b/src/hostnet_test/main_lwt.ml
index 33863f622..04a4d52ad 100644
--- a/src/hostnet_test/main_lwt.ml
+++ b/src/hostnet_test/main_lwt.ml
@@ -1,5 +1,3 @@
-open Lwt.Infix
-
 let src =
   let src = Logs.Src.create "test" ~doc:"Test the slirp stack" in
   Logs.Src.set_level src (Some Logs.Debug);
diff --git a/src/hostnet_test/main_uwt.ml b/src/hostnet_test/main_uwt.ml
index df86f9b99..0c240a649 100644
--- a/src/hostnet_test/main_uwt.ml
+++ b/src/hostnet_test/main_uwt.ml
@@ -1,5 +1,3 @@
-open Lwt.Infix
-
 let src =
   let src = Logs.Src.create "test" ~doc:"Test the slirp stack" in
   Logs.Src.set_level src (Some Logs.Debug);
diff --git a/src/hostnet_test/slirp_stack.ml b/src/hostnet_test/slirp_stack.ml
index 3e2a52a87..fab638b06 100644
--- a/src/hostnet_test/slirp_stack.ml
+++ b/src/hostnet_test/slirp_stack.ml
@@ -11,7 +11,7 @@ module Dns_policy = struct
   let config_of_ips ips =
     let open Dns_forward.Config in
     let servers = Server.Set.of_list (
-      List.map (fun (ip, port) ->
+      List.map (fun (ip, _) ->
         {
           Server.address = { Address.ip; port = 53 }; zones = Domain.Set.empty;
           timeout_ms = Some 2000; order = 0;
@@ -113,18 +113,17 @@ let peer_ip = Ipaddr.V4.of_string_exn "192.168.65.2"
 let local_ip = Ipaddr.V4.of_string_exn "192.168.65.1"
 let server_macaddr = Slirp.default_server_macaddr
 
-let global_arp_table : Slirp.arp_table = 
-  { mutex = Lwt_mutex.create (); 
-    table = [(local_ip, Slirp.default_server_macaddr)] 
+let global_arp_table : Slirp.arp_table =
+  { Slirp.mutex = Lwt_mutex.create ();
+    table = [(local_ip, Slirp.default_server_macaddr)]
   }
 
-let client_uuids : Slirp.uuid_table = 
-  { mutex = Lwt_mutex.create ();
+let client_uuids : Slirp.uuid_table =
+  { Slirp.mutex = Lwt_mutex.create ();
     table = Hashtbl.create 50;
   }
 
 let config_without_bridge =
-  let never, _ = Lwt.task () in
   {
     Slirp.peer_ip;
     local_ip;
@@ -182,7 +181,6 @@ let with_stack f =
   | Result.Ok flow ->
   Log.info (fun f -> f "Made a loopback connection");
   let client_macaddr = Slirp.default_client_macaddr in
-  let server_macaddr = Slirp.default_server_macaddr in
   let uuid = (match Uuidm.of_string "d1d9cd61-d0dc-4715-9bb3-4c11da7ad7a5" with
   | Some x -> x
   | None -> failwith "unable to parse test uuid") in
diff --git a/src/hostnet_test/suite.ml b/src/hostnet_test/suite.ml
index 700f92d00..5fdd2120f 100644
--- a/src/hostnet_test/suite.ml
+++ b/src/hostnet_test/suite.ml
@@ -77,11 +77,11 @@ let test_localhost_local_query server use_host () =
       (fun _ stack ->
         let resolver = DNS.create stack in
         Lwt_list.iter_s
-          (fun name ->
+          (fun _ ->
             let request =
               DNS.gethostbyname ~server resolver "localhost.local"
               >>= function
-              | (_ :: _) as ips ->
+              | _ :: _ ->
                 Log.err (fun f -> f "successfully resolved localhost.local: this shouldn't happen");
                 failwith "Successfully resolved localhost.local"
               | _ ->
@@ -139,7 +139,7 @@ let test_max_connections () =
               Host.Sockets.set_max_connections (Some 0);
               begin Client.TCPV4.create_connection (Client.tcpv4 stack) (ip, 80)
               >>= function
-              | `Ok flow ->
+              | `Ok _ ->
                 Log.err (fun f -> f "Connected to www.google.com, max_connections exceeded");
                 failwith "too many connections"
               | `Error _ ->
@@ -264,7 +264,7 @@ let rec count = function 0 -> [] | n -> () :: (count (n - 1))
 let test_stream_data connections length () =
   let t =
     DevNullServer.with_server
-      (fun { DevNullServer.local_port } ->
+      (fun { DevNullServer.local_port; _ } ->
         with_stack
           (fun _ stack ->
             Lwt_list.iter_p
diff --git a/src/hostnet_test/test_nat.ml b/src/hostnet_test/test_nat.ml
index 1ac8df475..0922d3040 100644
--- a/src/hostnet_test/test_nat.ml
+++ b/src/hostnet_test/test_nat.ml
@@ -80,7 +80,7 @@ module Make(Host: Sig.HOST) = struct
       let seen_source_ports = PortSet.empty in
       let t = { port; highest; seen_source_ports; c } in
       Client.listen_udpv4 stack ~port
-        (fun ~src ~dst ~src_port buffer ->
+        (fun ~src:_ ~dst:_ ~src_port buffer ->
            t.highest <- max t.highest (Cstruct.get_uint8 buffer 0);
            t.seen_source_ports <- PortSet.add src_port t.seen_source_ports;
            Log.debug (fun f -> f "Received UDP %d -> %d highest %d" src_port port t.highest);
@@ -88,13 +88,13 @@ module Make(Host: Sig.HOST) = struct
            Lwt.return_unit
         );
       t
-    let rec wait_for_data ~timeout ~highest t =
+    let wait_for_data ~highest t =
       if t.highest < highest then begin
         Lwt.pick [ Lwt_condition.wait t.c; Host.Time.sleep 1. ]
         >>= fun () ->
         Lwt.return (t.highest >= highest)
       end else Lwt.return true
-    let rec wait_for_ports ~timeout ~num t =
+    let wait_for_ports ~num t =
       if PortSet.cardinal t.seen_source_ports < num then begin
         Lwt.pick [ Lwt_condition.wait t.c; Host.Time.sleep 1. ]
         >>= fun () ->
@@ -106,7 +106,7 @@ module Make(Host: Sig.HOST) = struct
   let test_udp () =
     let t =
       EchoServer.with_server
-        (fun { EchoServer.local_port } ->
+        (fun { EchoServer.local_port; _ } ->
            with_stack
              (fun _ stack ->
                 let buffer = Cstruct.create 1024 in
@@ -121,7 +121,7 @@ module Make(Host: Sig.HOST) = struct
                   Log.debug (fun f -> f "Sending %d -> %d value %d" virtual_port local_port (Cstruct.get_uint8 buffer 0));
                   Client.UDPV4.write ~source_port:virtual_port ~dest_ip:Ipaddr.V4.localhost ~dest_port:local_port udpv4 buffer
                   >>= fun () ->
-                  UdpServer.wait_for_data ~timeout:1. ~highest:1 server
+                  UdpServer.wait_for_data ~highest:1 server
                   >>= function
                   | true -> Lwt.return_unit
                   | false -> loop (remaining - 1) in
@@ -136,7 +136,7 @@ module Make(Host: Sig.HOST) = struct
   let test_udp_2 () =
     let t =
       EchoServer.with_server
-        (fun { EchoServer.local_port } ->
+        (fun { EchoServer.local_port; _ } ->
            with_stack
              (fun _ stack ->
                 let buffer = Cstruct.create 1024 in
@@ -153,7 +153,7 @@ module Make(Host: Sig.HOST) = struct
                   Log.debug (fun f -> f "Sending %d -> %d value %d" virtual_port1 local_port (Cstruct.get_uint8 buffer 0));
                   Client.UDPV4.write ~source_port:virtual_port1 ~dest_ip:Ipaddr.V4.localhost ~dest_port:local_port udpv4 buffer
                   >>= fun () ->
-                  UdpServer.wait_for_data ~timeout:1. ~highest:1 server1
+                  UdpServer.wait_for_data ~highest:1 server1
                   >>= function
                   | true -> Lwt.return_unit
                   | false -> loop (remaining - 1) in
@@ -169,10 +169,10 @@ module Make(Host: Sig.HOST) = struct
                   Log.debug (fun f -> f "Sending %d -> %d value %d" virtual_port2 local_port (Cstruct.get_uint8 buffer 0));
                   Client.UDPV4.write ~source_port:virtual_port2 ~dest_ip:Ipaddr.V4.localhost ~dest_port:local_port udpv4 buffer
                   >>= fun () ->
-                  UdpServer.wait_for_data ~timeout:1. ~highest:2 server2
+                  UdpServer.wait_for_data ~highest:2 server2
                   >>= fun ok2 ->
                   (* The server should "multicast" the packet to the original "connection" *)
-                  UdpServer.wait_for_data ~timeout:1. ~highest:2 server1
+                  UdpServer.wait_for_data ~highest:2 server1
                   >>= fun ok1 ->
                   if ok1 && ok2 then Lwt.return_unit else loop (remaining - 1) in
                 loop 5
@@ -204,7 +204,7 @@ module Make(Host: Sig.HOST) = struct
                   Log.debug (fun f -> f "Sending %d -> %d value %d" virtual_port1 dest_port (Cstruct.get_uint8 buffer 0));
                   Client.UDPV4.write ~source_port:virtual_port1 ~dest_ip:Ipaddr.V4.localhost ~dest_port udpv4 buffer
                   >>= fun () ->
-                  UdpServer.wait_for_data ~timeout:1. ~highest:1 server1
+                  UdpServer.wait_for_data ~highest:1 server1
                   >>= function
                   | true -> Lwt.return_unit
                   | false -> loop (remaining - 1) in
@@ -225,7 +225,7 @@ module Make(Host: Sig.HOST) = struct
                   Log.debug (fun f -> f "Sending %d -> %d value %d" source_port dest_port (Cstruct.get_uint8 buffer 0));
                   Host.Sockets.Datagram.Udp.sendto client address buffer
                   >>= fun () ->
-                  UdpServer.wait_for_data ~timeout:1. ~highest:2 server1
+                  UdpServer.wait_for_data ~highest:2 server1
                   >>= function
                   | true -> Lwt.return_unit
                   | false -> loop (remaining - 1) in
@@ -240,7 +240,7 @@ module Make(Host: Sig.HOST) = struct
   let test_shared_nat_rule () =
     let t =
       EchoServer.with_server
-        (fun { EchoServer.local_port } ->
+        (fun { EchoServer.local_port; _ } ->
            with_stack
              (fun slirp_server stack ->
                 let buffer = Cstruct.create 1024 in
@@ -256,7 +256,7 @@ module Make(Host: Sig.HOST) = struct
                   Log.debug (fun f -> f "Sending %d -> %d value %d" virtual_port local_port (Cstruct.get_uint8 buffer 0));
                   Client.UDPV4.write ~source_port:virtual_port ~dest_ip:Ipaddr.V4.localhost ~dest_port:local_port udpv4 buffer
                   >>= fun () ->
-                  UdpServer.wait_for_data ~timeout:1. ~highest:1 server
+                  UdpServer.wait_for_data ~highest:1 server
                   >>= function
                   | true -> Lwt.return_unit
                   | false -> loop (remaining - 1) in
@@ -268,13 +268,13 @@ module Make(Host: Sig.HOST) = struct
                 (* Create another physical server and send traffic from the same
                    virtual address *)
                 EchoServer.with_server
-                  (fun { EchoServer.local_port } ->
+                  (fun { EchoServer.local_port; _ } ->
                      let rec loop remaining =
                        if remaining = 0 then failwith "Timed-out before UDP response arrived";
                        Log.debug (fun f -> f "Sending %d -> %d value %d" virtual_port local_port (Cstruct.get_uint8 buffer 0));
                        Client.UDPV4.write ~source_port:virtual_port ~dest_ip:Ipaddr.V4.localhost ~dest_port:local_port udpv4 buffer
                        >>= fun () ->
-                       UdpServer.wait_for_data ~timeout:1. ~highest:2 server
+                       UdpServer.wait_for_data ~highest:2 server
                        >>= function
                        | true -> Lwt.return_unit
                        | false -> loop (remaining - 1) in
@@ -292,9 +292,9 @@ module Make(Host: Sig.HOST) = struct
   let test_source_ports () =
     let t =
       EchoServer.with_server
-        (fun { EchoServer.local_port = local_port1 } ->
+        (fun { EchoServer.local_port = local_port1; _ } ->
           EchoServer.with_server
-            (fun { EchoServer.local_port = local_port2 } ->
+            (fun { EchoServer.local_port = local_port2; _ } ->
                with_stack
                  (fun _ stack ->
                     let buffer = Cstruct.create 1024 in
@@ -311,7 +311,7 @@ module Make(Host: Sig.HOST) = struct
                       Log.debug (fun f -> f "Sending %d -> %d value %d" virtual_port local_port2 (Cstruct.get_uint8 buffer 0));
                       Client.UDPV4.write ~source_port:virtual_port ~dest_ip:Ipaddr.V4.localhost ~dest_port:local_port2 udpv4 buffer
                       >>= fun () ->
-                      UdpServer.wait_for_ports ~timeout:1. ~num:2 server
+                      UdpServer.wait_for_ports ~num:2 server
                       >>= function
                       | true -> Lwt.return_unit
                       | false -> loop (remaining - 1) in
diff --git a/src/ofs/active_list.ml b/src/ofs/active_list.ml
index 699d76e00..d44920b4f 100644
--- a/src/ofs/active_list.ml
+++ b/src/ofs/active_list.ml
@@ -151,6 +151,8 @@ The directory will be deleted and replaced with a file of the same name.
     connection.fids := Types.Fid.Map.add fid Root !(connection.fids);
     return { Response.Attach.qid = root_qid }
 
+  exception Enoent
+
   let walk connection ~cancel:_ { Request.Walk.fid; newfid; wnames } =
     try
       let from = Types.Fid.Map.find fid !(connection.fids) in
@@ -168,19 +170,18 @@ The directory will be deleted and replaced with a file of the same name.
                 | Some _ -> []
               ) in
               (Entry entry, qid), qid :: qids
-            end else failwith "ENOENT"
+            end else raise Enoent
           | "ctl", Entry entry ->
             let qid = next_qid [] in
             (ControlFile entry, qid), qid :: qids
-          | _, _ -> failwith "ENOENT"
+          | _, _ -> raise Enoent
         ) ((from, next_qid []), []) wnames in
       connection.fids := Types.Fid.Map.add newfid (fst from) !(connection.fids);
       let wqids = List.rev wqids in
       return { Response.Walk.wqids }
     with
     | Not_found -> Error.badfid
-    | Failure "ENOENT" -> Error.enoent
-    | Failure "BADWALK" -> Error.badwalk
+    | Enoent -> Error.enoent
 
   let free_resource = function
     | ControlFile entry ->
diff --git a/src/ofs/jbuild b/src/ofs/jbuild
index eec317b76..70f955203 100644
--- a/src/ofs/jbuild
+++ b/src/ofs/jbuild
@@ -6,5 +6,6 @@
     mirage-types.lwt astring named-pipe.lwt
    ))
    (wrapped false)
+   (flags (:standard -warn-error "+1..49-3" -w "A-4-41-42-44"))
 ))