diff --git a/src/irmin-cli/cli.ml b/src/irmin-cli/cli.ml
index 5ef2a3cbe7..90c3cdcc06 100644
--- a/src/irmin-cli/cli.ml
+++ b/src/irmin-cli/cli.ml
@@ -19,6 +19,8 @@ open Cmdliner
 open Resolver
 module Graphql = Irmin_graphql_unix
 
+type eio = Import.eio
+
 let deprecated_info = (Term.info [@alert "-deprecated"])
 let deprecated_man_format = (Term.man_format [@alert "-deprecated"])
 let deprecated_eval_choice = (Term.eval_choice [@alert "-deprecated"])
@@ -53,7 +55,7 @@ let term_info title ~doc ~man =
   deprecated_info ~sdocs:global_option_section ~docs:global_option_section ~doc
     ~man title
 
-type command = (unit Term.t * Term.info[@alert "-deprecated"])
+type command = env:eio -> (unit Term.t * Term.info[@alert "-deprecated"])
 
 type sub = {
   name : string;
@@ -62,7 +64,8 @@ type sub = {
   term : unit Term.t;
 }
 
-let create_command c =
+let create_command c ~env =
+  let c = c ~env in
   let man = [ `S "DESCRIPTION"; `P c.doc ] @ c.man in
   (c.term, term_info c.name ~doc:c.doc ~man)
 
@@ -113,14 +116,14 @@ let run t = try t () with err -> print_exc err
 let mk (fn : 'a) : 'a Term.t = Term.(const (fun () -> fn) $ setup_log)
 
 (* INIT *)
-let init =
+let init ~env =
   {
     name = "init";
     doc = "Initialize a store.";
     man = [];
     term =
       (let init (S (_, _store, _)) = () in
-       Term.(mk init $ store ()));
+       Term.(mk init $ store ~env));
   }
 
 let print fmt = Fmt.kstr print_endline fmt
@@ -136,7 +139,7 @@ let branch f x = get "branch" f x
 let commit f x = get "commit" f x
 
 (* GET *)
-let get =
+let get ~env =
   {
     name = "get";
     doc = "Read the value associated with a key.";
@@ -152,11 +155,11 @@ let get =
              exit 1
          | Some v -> print "%a" (Irmin.Type.pp S.Contents.t) v
        in
-       Term.(mk get $ store () $ path));
+       Term.(mk get $ store ~env $ path));
   }
 
 (* LIST *)
-let list =
+let list ~env =
   {
     name = "list";
     doc = "List subdirectories.";
@@ -180,11 +183,11 @@ let list =
          in
          List.iter (print "%a" pp) paths
        in
-       Term.(mk list $ store () $ path_or_empty));
+       Term.(mk list $ store ~env $ path_or_empty));
   }
 
 (* TREE *)
-let tree =
+let tree ~env =
   {
     name = "tree";
     doc = "List the store contents.";
@@ -236,7 +239,7 @@ let tree =
              print "%s%s%s" k dots v)
            all
        in
-       Term.(mk tree $ store ()));
+       Term.(mk tree $ store ~env));
   }
 
 let author =
@@ -248,7 +251,7 @@ let message =
   Arg.(value & opt (some string) None & doc)
 
 (* SET *)
-let set =
+let set ~env =
   {
     name = "set";
     doc = "Update the value associated with a key.";
@@ -267,11 +270,11 @@ let set =
          let value = value S.Contents.t v in
          S.set_exn t ~info:(info (module S) ?author "%s" message) path value
        in
-       Term.(mk set $ store () $ author $ message $ path $ v));
+       Term.(mk set $ store ~env $ author $ message $ path $ v));
   }
 
 (* REMOVE *)
-let remove =
+let remove ~env =
   {
     name = "remove";
     doc = "Delete a key.";
@@ -288,7 +291,7 @@ let remove =
            ~info:(info (module S) ?author "%s" message)
            (key S.Path.t path)
        in
-       Term.(mk remove $ store () $ author $ message $ path));
+       Term.(mk remove $ store ~env $ author $ message $ path));
   }
 
 let apply e f =
@@ -298,7 +301,7 @@ let apply e f =
   | r, _ -> r
 
 (* CLONE *)
-let clone =
+let clone ~env =
   {
     name = "clone";
     doc = "Copy a remote respository to a local store";
@@ -316,11 +319,11 @@ let clone =
          | Ok `Empty -> ()
          | Error (`Msg e) -> failwith e
        in
-       Term.(mk clone $ Resolver.remote () $ depth));
+       Term.(mk clone $ Resolver.remote ~env $ depth));
   }
 
 (* FETCH *)
-let fetch =
+let fetch ~env =
   {
     name = "fetch";
     doc = "Download objects and refs from another repository.";
@@ -338,11 +341,11 @@ let fetch =
          let _ = Sync.pull_exn t x `Set in
          ()
        in
-       Term.(mk fetch $ Resolver.remote ()));
+       Term.(mk fetch $ Resolver.remote ~env));
   }
 
 (* MERGE *)
-let merge =
+let merge ~env =
   {
     name = "merge";
     doc = "Merge branches.";
@@ -371,11 +374,11 @@ let merge =
          let doc = Arg.info ~docv:"BRANCH" ~doc:"Branch to merge from." [] in
          Arg.(required & pos 0 (some string) None & doc)
        in
-       Term.(mk merge $ store () $ author $ message $ branch_name));
+       Term.(mk merge $ store ~env $ author $ message $ branch_name));
   }
 
 (* PULL *)
-let pull =
+let pull ~env =
   {
     name = "pull";
     doc = "Fetch and merge with another repository.";
@@ -394,11 +397,11 @@ let pull =
          in
          ()
        in
-       Term.(mk pull $ remote () $ author $ message));
+       Term.(mk pull $ remote ~env $ author $ message));
   }
 
 (* PUSH *)
-let push =
+let push ~env =
   {
     name = "push";
     doc = "Update remote references along with associated objects.";
@@ -414,11 +417,11 @@ let push =
          let _ = Sync.push_exn t x in
          ()
        in
-       Term.(mk push $ remote ()));
+       Term.(mk push $ remote ~env));
   }
 
 (* SNAPSHOT *)
-let snapshot =
+let snapshot ~env =
   {
     name = "snapshot";
     doc = "Return a snapshot for the current state of the database.";
@@ -432,11 +435,11 @@ let snapshot =
          print "%a" S.Commit.pp_hash k;
          ()
        in
-       Term.(mk snapshot $ store ()));
+       Term.(mk snapshot $ store ~env));
   }
 
 (* REVERT *)
-let revert =
+let revert ~env =
   {
     name = "revert";
     doc = "Revert the contents of the store to a previous state.";
@@ -457,7 +460,7 @@ let revert =
          | Some s -> S.Head.set t s
          | None -> failwith "invalid commit"
        in
-       Term.(mk revert $ store () $ snapshot));
+       Term.(mk revert $ store ~env $ snapshot));
   }
 
 (* WATCH *)
@@ -543,7 +546,7 @@ let handle_diff (type a b)
        and type Schema.Metadata.t = S.metadata)
     diff command proc
 
-let watch =
+let watch ~env =
   {
     name = "watch";
     doc = "Get notifications when values change.";
@@ -573,11 +576,11 @@ let watch =
          let doc = Arg.info ~docv:"COMMAND" ~doc:"Command to execute" [] in
          Arg.(value & pos_right 0 string [] & doc)
        in
-       Term.(mk watch $ store () $ path $ command));
+       Term.(mk watch $ store ~env $ path $ command));
   }
 
 (* DOT *)
-let dot =
+let dot ~env =
   {
     name = "dot";
     doc = "Dump the contents of the store as a Graphviz file.";
@@ -639,7 +642,7 @@ let dot =
            in
            if i <> 0 then [%logs.err "The %s.dot is corrupted" basename])
        in
-       Term.(mk dot $ store () $ basename $ depth $ no_dot_call $ full));
+       Term.(mk dot $ store ~env $ basename $ depth $ no_dot_call $ full));
   }
 
 let config_man =
@@ -676,7 +679,7 @@ let config_man =
     @ help_sections )
 
 (* HELP *)
-let help =
+let help ~env:_ =
   {
     name = "help";
     doc = "Display help about Irmin and Irmin commands.";
@@ -710,7 +713,7 @@ let help =
   }
 
 (* GRAPHQL *)
-let graphql =
+let graphql ~env =
   {
     name = "graphql";
     doc = "Run a graphql server.";
@@ -748,19 +751,19 @@ let graphql =
            ~mode:(`TCP (`Port port))
            server
        in
-       Term.(mk graphql $ store () $ port $ addr));
+       Term.(mk graphql $ store ~env $ port $ addr));
   }
 
 (* SERVER *)
-let server =
+let server ~env =
   {
     name = "server";
     doc = "Run irmin-server.";
     man = [];
-    term = Server.main_term;
+    term = Server.main_term ~env;
   }
 
-let options =
+let options ~env =
   {
     name = "options";
     doc = "Get information about backend specific configuration options.";
@@ -768,26 +771,22 @@ let options =
     term =
       (let options (store, hash, contents) =
          let module Conf = Irmin.Backend.Conf in
-         let store, _ = Resolver.load_config ?store ?hash ?contents () in
+         let store, _ = Resolver.load_config ~env ?store ?hash ?contents () in
          let spec = Store.spec store in
          Seq.iter
            (fun (Conf.K k) ->
              let name = Conf.name k in
              if name = "root" || name = "uri" then ()
              else
-               let ty = Conf.ty k in
+               let ty = Conf.typename k in
                let doc = Conf.doc k |> Option.value ~default:"" in
-               let ty =
-                 Fmt.str "%a" Irmin.Type.pp_ty ty
-                 |> Astring.String.filter (fun c -> c <> '\n')
-               in
                Fmt.pr "%s: %s\n\t%s\n" name ty doc)
            (Conf.Spec.keys spec)
        in
        Term.(mk options $ Store.term ()));
   }
 
-let branches =
+let branches ~env =
   {
     name = "branches";
     doc = "List branches";
@@ -800,7 +799,7 @@ let branches =
          let branches = S.Branch.list (S.repo t) in
          List.iter (Fmt.pr "%a\n" (Irmin.Type.pp S.branch_t)) branches
        in
-       Term.(mk branches $ store ()));
+       Term.(mk branches $ store ~env));
   }
 
 let weekday Unix.{ tm_wday; _ } =
@@ -830,7 +829,7 @@ let month Unix.{ tm_mon; _ } =
   | 11 -> "Dec"
   | _ -> assert false
 
-let log =
+let log ~env =
   {
     name = "log";
     doc = "List commits";
@@ -911,10 +910,59 @@ let log =
              ()
            with Sys_error s when String.equal s "Broken pipe" -> ()
        in
-       Term.(mk commits $ store () $ plain $ pager $ num $ skip $ reverse));
+       Term.(mk commits $ store ~env $ plain $ pager $ num $ skip $ reverse));
   }
 
-let default =
+let commands : (env:eio -> sub) list =
+  [
+    help;
+    init;
+    get;
+    set;
+    remove;
+    list;
+    tree;
+    clone;
+    fetch;
+    merge;
+    pull;
+    push;
+    snapshot;
+    revert;
+    watch;
+    dot;
+    graphql;
+    server;
+    options;
+    branches;
+    log;
+  ]
+
+let common_commands =
+  [
+    init;
+    get;
+    set;
+    remove;
+    list;
+    tree;
+    clone;
+    fetch;
+    merge;
+    pull;
+    push;
+    snapshot;
+    revert;
+    watch;
+    dot;
+    graphql;
+    server;
+    options;
+    branches;
+    log;
+  ]
+
+let default ~env =
   let doc = "Irmin, the database that never forgets." in
   let man =
     [
@@ -933,66 +981,28 @@ let default =
       "usage: irmin [--version]\n\
       \             [--help]\n\
       \             <command> [<args>]\n\n\
-       The most commonly used subcommands are:\n\
-      \    init        %s\n\
-      \    get         %s\n\
-      \    set         %s\n\
-      \    remove      %s\n\
-      \    list        %s\n\
-      \    tree        %s\n\
-      \    clone       %s\n\
-      \    fetch       %s\n\
-      \    merge       %s\n\
-      \    pull        %s\n\
-      \    push        %s\n\
-      \    snapshot    %s\n\
-      \    revert      %s\n\
-      \    watch       %s\n\
-      \    dot         %s\n\
-      \    graphql     %s\n\
-      \    server      %s\n\
-      \    options     %s\n\
-      \    branches    %s\n\
-      \    log         %s\n\n\
-       See `irmin help <command>` for more information on a specific command.\n\
-       %!"
-      init.doc get.doc set.doc remove.doc list.doc tree.doc clone.doc fetch.doc
-      merge.doc pull.doc push.doc snapshot.doc revert.doc watch.doc dot.doc
-      graphql.doc server.doc options.doc branches.doc log.doc
+       The most commonly used subcommands are:\n";
+    List.iter
+      (fun cmd ->
+        let cmd = cmd ~env in
+        Fmt.pr "    %-11s %s\n" cmd.name cmd.doc)
+      common_commands;
+    Fmt.pr
+      "\n\
+       See `irmin help <command>` for more information on a specific command.@."
   in
   ( Term.(mk usage $ const ()),
     deprecated_info "irmin" ~version:Irmin.version ~sdocs:global_option_section
       ~doc ~man )
 
-let commands =
-  List.map create_command
-    [
-      help;
-      init;
-      get;
-      set;
-      remove;
-      list;
-      tree;
-      clone;
-      fetch;
-      merge;
-      pull;
-      push;
-      snapshot;
-      revert;
-      watch;
-      dot;
-      graphql;
-      server;
-      options;
-      branches;
-      log;
-    ]
+let commands = List.map create_command commands
 
 let run ~default:x y =
   Eio_main.run @@ fun env ->
-  Irmin_fs.run env#fs @@ fun () ->
   Lwt_eio.with_event_loop ~clock:env#clock @@ fun _ ->
   Irmin.Backend.Watch.set_listen_dir_hook Irmin_watcher.hook;
-  match deprecated_eval_choice x y with `Error _ -> exit 1 | _ -> ()
+  let env = (env :> eio) in
+  let run cmd = cmd ~env in
+  match deprecated_eval_choice (run x) (List.map run y) with
+  | `Error _ -> exit 1
+  | _ -> ()
diff --git a/src/irmin-cli/cli.mli b/src/irmin-cli/cli.mli
index 6141f56afa..70a4f45b95 100644
--- a/src/irmin-cli/cli.mli
+++ b/src/irmin-cli/cli.mli
@@ -16,7 +16,10 @@
 
 (** CLI commands. *)
 
-type command = (unit Cmdliner.Term.t * Cmdliner.Term.info[@alert "-deprecated"])
+type eio = Import.eio
+
+type command =
+  env:eio -> (unit Cmdliner.Term.t * Cmdliner.Term.info[@alert "-deprecated"])
 (** [Cmdliner] commands. *)
 
 val default : command
@@ -38,5 +41,5 @@ type sub = {
 }
 (** Subcommand. *)
 
-val create_command : sub -> command
+val create_command : (env:eio -> sub) -> command
 (** Build a subcommand. *)
diff --git a/src/irmin-cli/dune b/src/irmin-cli/dune
index 8496c072ab..53ba1c313d 100644
--- a/src/irmin-cli/dune
+++ b/src/irmin-cli/dune
@@ -19,6 +19,7 @@
   cohttp-lwt-unix
   unix
   yaml
+  eio
   eio_main
   lwt_eio)
  (preprocess
diff --git a/src/irmin-cli/import.ml b/src/irmin-cli/import.ml
index fff6d09bdb..bb36eaba59 100644
--- a/src/irmin-cli/import.ml
+++ b/src/irmin-cli/import.ml
@@ -15,3 +15,7 @@
  *)
 
 include Irmin.Export_for_backends
+
+type eio =
+  < cwd : Eio.Fs.dir_ty Eio.Path.t
+  ; clock : float Eio.Time.clock_ty Eio.Time.clock >
diff --git a/src/irmin-cli/resolver.ml b/src/irmin-cli/resolver.ml
index 4d2106ef08..5c9dea5ced 100644
--- a/src/irmin-cli/resolver.ml
+++ b/src/irmin-cli/resolver.ml
@@ -23,21 +23,23 @@ let global_option_section = "COMMON OPTIONS"
 
 module Conf = Irmin.Backend.Conf
 
-let try_parse ty v =
-  match Irmin.Type.of_string ty v with
+let try_parse of_string v =
+  match of_string v with
   | Error e -> (
       let x = Format.sprintf "{\"some\": %s}" v in
-      match Irmin.Type.of_string ty x with
+      match of_string x with
       | Error _ ->
           let y = Format.sprintf "{\"some\": \"%s\"}" v in
-          Irmin.Type.of_string ty y |> Result.map_error (fun _ -> e)
+          of_string y |> Result.map_error (fun _ -> e)
       | v -> v)
   | v -> v
 
 let pconv t =
   let pp = Irmin.Type.pp t in
   let parse s =
-    match try_parse t s with Ok x -> `Ok x | Error (`Msg e) -> `Error e
+    match try_parse (Irmin.Type.of_string t) s with
+    | Ok x -> `Ok x
+    | Error (`Msg e) -> `Error e
   in
   (parse, pp)
 
@@ -296,7 +298,14 @@ module Store = struct
     v spec (module S)
 
   let mem = create Irmin_mem.Conf.spec (module Irmin_mem)
-  let fs = create Irmin_fs.Conf.spec (module Irmin_fs_unix)
+
+  let fs env =
+    let spec =
+      Irmin_fs_unix.spec ~path:(Eio.Stdenv.cwd env)
+        ~clock:(Eio.Stdenv.clock env)
+    in
+    create spec (module Irmin_fs_unix)
+
   let git (module C : Irmin.Contents.S) = v_git (module Xgit.FS.KV (C))
   let git_mem (module C : Irmin.Contents.S) = v_git (module Xgit.Mem.KV (C))
 
@@ -324,23 +333,24 @@ module Store = struct
   let all =
     ref
       [
-        ("git", Fixed_hash git);
-        ("git-mem", Fixed_hash git_mem);
-        ("fs", Variable_hash fs);
-        ("mem", Variable_hash mem);
-        ("pack", Variable_hash pack);
-        ("tezos", Fixed tezos);
+        ("git", fun _ -> Fixed_hash git);
+        ("git-mem", fun _ -> Fixed_hash git_mem);
+        ("fs", fun env -> Variable_hash (fs env));
+        ("mem", fun _ -> Variable_hash mem);
+        ("pack", fun _ -> Variable_hash pack);
+        ("tezos", fun _ -> Fixed tezos);
       ]
 
   let default = "git" |> fun n -> ref (n, List.assoc n !all)
 
   let add name ?default:(x = false) m =
+    let m (_ : eio) = m in
     all := (name, m) :: !all;
     if x then default := (name, m)
 
-  let find name =
+  let find name env =
     match List.assoc_opt (String.Ascii.lowercase name) !all with
-    | Some s -> s
+    | Some s -> s env
     | None ->
         let valid = String.concat ~sep:", " (List.split !all |> fst) in
         let msg =
@@ -456,10 +466,10 @@ let parse_config ?root y spec =
         | Some (Irmin.Backend.Conf.K k), Some v ->
             let v = json_of_yaml v |> Yojson.Basic.to_string in
             let v =
-              match Irmin.Type.of_json_string (Conf.ty k) v with
+              match Conf.of_json_string k v with
               | Error _ ->
                   let v = Format.sprintf "{\"some\": %s}" v in
-                  Irmin.Type.of_json_string (Conf.ty k) v |> Result.get_ok
+                  Conf.of_json_string k v |> Result.get_ok
               | Ok v -> v
             in
             Conf.add config k v
@@ -475,7 +485,7 @@ let parse_config ?root y spec =
   let config =
     match (root, Conf.Spec.find_key spec "root") with
     | Some root, Some (K r) ->
-        let v = Irmin.Type.of_string (Conf.ty r) root |> Result.get_ok in
+        let v = Conf.of_string r root |> Result.get_ok in
         Conf.add config r v
     | _ -> config
   in
@@ -489,7 +499,7 @@ let load_plugin ?plugin config =
       | Ok (Some v) -> Dynlink.loadfile_private (Yaml.Util.to_string_exn v)
       | _ -> ())
 
-let get_store ?plugin config (store, hash, contents) =
+let get_store ~env ?plugin config (store, hash, contents) =
   let () = load_plugin ?plugin config in
   let store =
     match store with
@@ -500,6 +510,7 @@ let get_store ?plugin config (store, hash, contents) =
             match store with Some s -> Store.find s | None -> Store.find s)
         | _ -> snd !Store.default)
   in
+  let store = store env in
   let contents =
     match contents with
     | Some s -> Contents.find s
@@ -532,9 +543,9 @@ let get_store ?plugin config (store, hash, contents) =
       | _ ->
           Fmt.failwith "Cannot customize the hash function for the given store")
 
-let load_config ?plugin ?root ?config_path ?store ?hash ?contents () =
+let load_config ~env ?plugin ?root ?config_path ?store ?hash ?contents () =
   let y = read_config_file config_path in
-  let store = get_store ?plugin y (store, hash, contents) in
+  let store = get_store ~env ?plugin y (store, hash, contents) in
   let spec = Store.spec store in
   let config = parse_config ?root y spec in
   (store, config)
@@ -564,10 +575,10 @@ let get_commit (type a b)
   | None -> of_string (find_key config "commit")
   | Some t -> of_string (Some t)
 
-let build_irmin_config config root opts (store, hash, contents) branch commit
-    plugin : store =
+let build_irmin_config ~env config root opts (store, hash, contents) branch
+    commit plugin : store =
   let (T { impl; spec; remote }) =
-    get_store ?plugin config (store, hash, contents)
+    get_store ~env ?plugin config (store, hash, contents)
   in
   let (module S) = Store.Impl.generic_keyed impl in
   let branch = get_branch (module S) config branch in
@@ -586,8 +597,7 @@ let build_irmin_config config root opts (store, hash, contents) branch commit
             | Some x -> x
             | None -> invalid_arg ("opt: " ^ k)
         in
-        let ty = Conf.ty key in
-        let v = try_parse ty v |> Result.get_ok in
+        let v = try_parse (Conf.of_string key) v |> Result.get_ok in
         let config = Conf.add config key v in
         config)
       config (List.flatten opts)
@@ -626,10 +636,10 @@ let plugin =
   let doc = "Register new contents, store or hash types" in
   Arg.(value & opt (some string) None & info ~doc [ "plugin" ])
 
-let store () =
+let store ~env =
   let create plugin store (root, config_path, opts) branch commit =
     let y = read_config_file config_path in
-    build_irmin_config y root opts store branch commit plugin
+    build_irmin_config ~env y root opts store branch commit plugin
   in
   Term.(const create $ plugin $ Store.term () $ config_term $ branch $ commit)
 
@@ -653,7 +663,7 @@ type Irmin.remote += R of Cohttp.Header.t option * string
 (* FIXME: this is a very crude heuristic to choose the remote
    kind. Would be better to read the config file and look for remote
    alias. *)
-let infer_remote hash contents branch headers str =
+let infer_remote ~env hash contents branch headers str =
   let hash = match hash with None -> snd !Hash.default | Some c -> c in
   let contents =
     match contents with
@@ -664,7 +674,7 @@ let infer_remote hash contents branch headers str =
     let r =
       if Sys.file_exists (str / ".git") then Store.git contents
       else if Sys.file_exists (str / "store.dict") then Store.pack hash contents
-      else Store.fs hash contents
+      else Store.fs env hash contents
     in
     match r with
     | Store.T { impl; spec; _ } ->
@@ -673,7 +683,7 @@ let infer_remote hash contents branch headers str =
         let config =
           match Conf.Spec.find_key spec "root" with
           | Some (K r) ->
-              let v = Irmin.Type.of_string (Conf.ty r) str |> Result.get_ok in
+              let v = Conf.of_string r str |> Result.get_ok in
               Conf.add config r v
           | _ -> config
         in
@@ -691,7 +701,7 @@ let infer_remote hash contents branch headers str =
     in
     R (headers, str)
 
-let remote () =
+let remote ~env =
   let repo =
     let doc =
       Arg.info ~docv:"REMOTE"
@@ -703,9 +713,10 @@ let remote () =
       headers str =
     let y = read_config_file config_path in
     let store =
-      build_irmin_config y root opts (store, hash, contents) branch commit None
+      build_irmin_config ~env y root opts (store, hash, contents) branch commit
+        None
     in
-    let remote () = infer_remote hash contents branch headers str in
+    let remote () = infer_remote ~env hash contents branch headers str in
     (store, remote)
   in
   Term.(
diff --git a/src/irmin-cli/resolver.mli b/src/irmin-cli/resolver.mli
index 9fbc8f637f..fc90d466f2 100644
--- a/src/irmin-cli/resolver.mli
+++ b/src/irmin-cli/resolver.mli
@@ -43,6 +43,8 @@ type contents = Contents.t
 
 (** {1 Global Configuration} *)
 
+type eio := Import.eio
+
 module Store : sig
   module Impl : sig
     (** The type of {i implementations} of an Irmin store.
@@ -86,10 +88,10 @@ module Store : sig
     t
 
   val mem : hash -> contents -> t
-  val fs : hash -> contents -> t
+  val fs : eio -> hash -> contents -> t
   val git : contents -> t
   val pack : hash -> contents -> t
-  val find : string -> store_functor
+  val find : string -> eio -> store_functor
   val add : string -> ?default:bool -> store_functor -> unit
   val spec : t -> Irmin.Backend.Conf.Spec.t
   val generic_keyed : t -> (module Irmin.Generic_key.S)
@@ -103,6 +105,7 @@ end
 (** {1 Stores} *)
 
 val load_config :
+  env:eio ->
   ?plugin:string ->
   ?root:string ->
   ?config_path:string ->
@@ -126,10 +129,10 @@ val load_config :
 type store =
   | S : 'a Store.Impl.t * (unit -> 'a) * Store.remote_fn option -> store
 
-val store : unit -> store Cmdliner.Term.t
+val store : env:eio -> store Cmdliner.Term.t
 (** Parse the command-line arguments and then the config file. *)
 
 type Irmin.remote += R of Cohttp.Header.t option * string
 
-val remote : unit -> (store * (unit -> Irmin.remote)) Cmdliner.Term.t
+val remote : env:eio -> (store * (unit -> Irmin.remote)) Cmdliner.Term.t
 (** Parse a remote store location. *)
diff --git a/src/irmin-cli/server.ml b/src/irmin-cli/server.ml
index 380615d2a6..20471e2ca6 100644
--- a/src/irmin-cli/server.ml
+++ b/src/irmin-cli/server.ml
@@ -29,10 +29,11 @@ let setup_log =
   Cmdliner.Term.(
     const setup_log $ Fmt_cli.style_renderer () $ Logs_cli.level ())
 
-let main ~readonly ~root ~uri ~tls ~store ~contents ~hash ~dashboard
+let main ~env ~readonly ~root ~uri ~tls ~store ~contents ~hash ~dashboard
     ~config_path (module Codec : Conn.Codec.S) fingerprint =
+  Lwt_eio.run_lwt @@ fun () ->
   let store, config =
-    Resolver.load_config ?root ?config_path ?store ?hash ?contents ()
+    Resolver.load_config ~env ?root ?config_path ?store ?hash ?contents ()
   in
   let config = Irmin_server.Cli.Conf.v config uri in
   let (module Store : Irmin.Generic_key.S) =
@@ -61,16 +62,15 @@ let main ~readonly ~root ~uri ~tls ~store ~contents ~hash ~dashboard
     Logs.app (fun l -> l "Listening on %a, store: %s" Uri.pp_hum uri root);
     Server.serve server
 
-let main readonly root uri tls (store, hash, contents) codec config_path
+let main ~env readonly root uri tls (store, hash, contents) codec config_path
     dashboard fingerprint () =
   let codec =
     match codec with
     | `Bin -> (module Conn.Codec.Bin : Conn.Codec.S)
     | `Json -> (module Conn.Codec.Json)
   in
-  Lwt_main.run
-  @@ main ~readonly ~root ~uri ~tls ~store ~contents ~hash ~config_path
-       ~dashboard codec fingerprint
+  main ~env ~readonly ~root ~uri ~tls ~store ~contents ~hash ~config_path
+    ~dashboard codec fingerprint
 
 open Cmdliner
 
@@ -107,9 +107,9 @@ let dashboard =
   in
   Arg.(value @@ opt (some int) None doc)
 
-let main_term =
+let main_term ~env =
   Term.(
-    const main
+    const (main ~env)
     $ readonly
     $ root
     $ Irmin_server.Cli.uri
diff --git a/src/irmin-client/unix/bin/client.ml b/src/irmin-client/unix/bin/client.ml
index 8ac3c90651..63bd18f250 100644
--- a/src/irmin-client/unix/bin/client.ml
+++ b/src/irmin-client/unix/bin/client.ml
@@ -260,7 +260,7 @@ let iterations =
   in
   Arg.(value @@ opt int 1 doc)
 
-let config =
+let config ~env =
   let create uri (branch : string option) tls (store, hash, contents) codec
       config_path () =
     let codec =
@@ -270,7 +270,7 @@ let config =
     in
     let (module Codec) = codec in
     let store, config =
-      Irmin_cli.Resolver.load_config ?config_path ?store ?hash ?contents ()
+      Irmin_cli.Resolver.load_config ~env ?config_path ?store ?hash ?contents ()
     in
     let config = Irmin_server.Cli.Conf.v config uri in
     let (module Store : Irmin.Generic_key.S) =
@@ -298,6 +298,8 @@ let help =
     (Term.info "irmin-client" [@alert "-deprecated"]) )
 
 let[@alert "-deprecated"] () =
+  Eio_main.run @@ fun env ->
+  let config = config ~env:(env :> Irmin_cli.eio) in
   Term.exit
   @@ Term.eval_choice help
        [
diff --git a/src/irmin-fs/irmin_fs.ml b/src/irmin-fs/irmin_fs.ml
index c08c50353e..4fdc93759f 100644
--- a/src/irmin-fs/irmin_fs.ml
+++ b/src/irmin-fs/irmin_fs.ml
@@ -15,43 +15,49 @@
  *)
 
 open! Import
-open Eio
 open Astring
 
 let src = Logs.Src.create "irmin.fs" ~doc:"Irmin disk persistence"
 
 module Log = (val Logs.src_log src : Logs.LOG)
 
-let ( / ) = Path.( / )
+let ( / ) = Filename.concat
 
 module type Config = sig
-  val dir : Fs.dir_ty Path.t -> Fs.dir_ty Path.t
+  val dir : string -> string
   val file_of_key : string -> string
   val key_of_file : string -> string
 end
 
 module type IO = sig
-  type path = Fs.dir_ty Path.t
+  type io
 
-  val rec_files : path -> path list
-  val file_exists : path -> bool
-  val read_file : path -> string option
-  val mkdir : path -> unit
+  val io_of_config : Irmin.config -> io
+
+  type path = string
+
+  val rec_files : io:io -> path -> path list
+  val file_exists : io:io -> path -> bool
+  val read_file : io:io -> path -> string option
+  val mkdir : io:io -> path -> unit
 
   type lock
 
-  val lock_file : path -> lock
-  val write_file : ?temp_dir:path -> ?lock:lock -> path -> string -> unit
+  val lock_file : io:io -> path -> lock
+
+  val write_file :
+    io:io -> temp_dir:path -> ?lock:lock -> path -> string -> unit
 
   val test_and_set_file :
-    ?temp_dir:path ->
+    io:io ->
+    temp_dir:path ->
     lock:lock ->
     path ->
     test:string option ->
     set:string option ->
     bool
 
-  val remove_file : ?lock:lock -> path -> unit
+  val remove_file : io:io -> ?lock:lock -> path -> unit
 end
 
 (* ~path *)
@@ -76,15 +82,15 @@ module Read_only_ext
 struct
   type key = K.t
   type value = V.t
-  type 'a t = { path : Fs.dir_ty Path.t }
+  type 'a t = { path : string; io : IO.io }
 
   let get_path config = Option.value Conf.(find_root config) ~default:"."
 
   let v config =
-    let fs = Irmin.Backend.Conf.Env.fs () in
-    let path = Path.(fs / get_path config) in
-    IO.mkdir path;
-    { path }
+    let io = IO.io_of_config config in
+    let path = get_path config in
+    IO.mkdir ~io path;
+    { path; io }
 
   let close _ = ()
   let cast t = (t :> read_write t)
@@ -93,12 +99,13 @@ struct
   let file_of_key { path; _ } key =
     path / S.file_of_key (Irmin.Type.to_string K.t key)
 
-  let lock_of_key { path; _ } key =
-    IO.lock_file (path / "lock" / S.file_of_key (Irmin.Type.to_string K.t key))
+  let lock_of_key { io; path } key =
+    IO.lock_file ~io
+      (path / "lock" / S.file_of_key (Irmin.Type.to_string K.t key))
 
   let mem t key =
     let file = file_of_key t key in
-    IO.file_exists file
+    IO.file_exists ~io:t.io file
 
   let of_bin_string = Irmin.Type.(unstage (of_bin_string V.t))
 
@@ -113,17 +120,17 @@ struct
 
   let find t key =
     [%log.debug "find %a" pp_key key];
-    match IO.read_file (file_of_key t key) with
+    match IO.read_file ~io:t.io (file_of_key t key) with
     | None -> None
     | Some x -> value x
 
-  let list t =
+  let list { path; io } =
     [%log.debug "list"];
-    let files = IO.rec_files (S.dir t.path) in
+    let files = IO.rec_files ~io (S.dir path) in
     let files =
-      let p = String.length (snd t.path) in
+      let p = String.length path in
       List.fold_left
-        (fun acc (_, file) ->
+        (fun acc file ->
           let n = String.length file in
           if n <= p + 1 then acc
           else
@@ -156,11 +163,11 @@ struct
     [%log.debug "add %a" pp_key key];
     let file = file_of_key t key in
     let temp_dir = temp_dir t in
-    match IO.file_exists file with
+    match IO.file_exists ~io:t.io file with
     | true -> ()
     | false ->
         let str = to_bin_string value in
-        IO.write_file ~temp_dir file str
+        IO.write_file ~io:t.io ~temp_dir file str
 end
 
 module Atomic_write_ext
@@ -217,7 +224,7 @@ struct
           [%log.err "listen_dir: %s" e];
           None
     in
-    W.listen_dir t.w (snd dir) ~key ~value:(RO.find t.t)
+    W.listen_dir t.w dir ~key ~value:(RO.find t.t)
 
   let watch_key t key ?init f =
     let stop = listen_dir t in
@@ -240,14 +247,14 @@ struct
     let temp_dir = temp_dir t in
     let file = RO.file_of_key t.t key in
     let lock = RO.lock_of_key t.t key in
-    IO.write_file ~temp_dir file ~lock (raw_value value);
+    IO.write_file ~io:t.t.io ~temp_dir file ~lock (raw_value value);
     W.notify t.w key (Some value)
 
   let remove t key =
     [%log.debug "remove %a" RO.pp_key key];
     let file = RO.file_of_key t.t key in
     let lock = RO.lock_of_key t.t key in
-    let () = IO.remove_file ~lock file in
+    let () = IO.remove_file ~io:t.t.io ~lock file in
     W.notify t.w key None
 
   let test_and_set t key ~test ~set =
@@ -257,8 +264,8 @@ struct
     let lock = RO.lock_of_key t.t key in
     let raw_value = function None -> None | Some v -> Some (raw_value v) in
     let b =
-      IO.test_and_set_file file ~temp_dir ~lock ~test:(raw_value test)
-        ~set:(raw_value set)
+      IO.test_and_set_file ~io:t.t.io file ~temp_dir ~lock
+        ~test:(raw_value test) ~set:(raw_value set)
     in
     let () = if b then W.notify t.w key set in
     b
@@ -266,7 +273,8 @@ struct
   let clear t =
     [%log.debug "clear"];
     let remove_file key () =
-      IO.remove_file ~lock:(RO.lock_of_key t.t key) (RO.file_of_key t.t key)
+      IO.remove_file ~io:t.t.io ~lock:(RO.lock_of_key t.t key)
+        (RO.file_of_key t.t key)
     in
     list t |> fun keys -> Eio.Fiber.all (List.map remove_file keys)
 end
@@ -330,26 +338,31 @@ module KV (IO : IO) = struct
 end
 
 module IO_mem = struct
+  type io = unit
+
+  let io_of_config _ = ()
+
+  type path = string
+
   type t = {
     watches : (string, string -> unit) Hashtbl.t;
-    files : (Fs.dir_ty Path.t, string) Hashtbl.t;
+    files : (path, string) Hashtbl.t;
   }
 
   let t = { watches = Hashtbl.create 3; files = Hashtbl.create 13 }
 
-  type path = Fs.dir_ty Path.t
   type lock = Eio.Mutex.t
 
   let locks = Hashtbl.create 10
 
-  let lock_file (_, file) =
+  let lock_file ~io:() file =
     try Hashtbl.find locks file
     with Not_found ->
       let l = Eio.Mutex.create () in
       Hashtbl.add locks file l;
       l
 
-  let with_lock l f =
+  let with_lock ~io:() l f =
     match l with None -> f () | Some l -> Eio.Mutex.use_rw ~protect:false l f
 
   let set_listen_hook () =
@@ -363,29 +376,28 @@ module IO_mem = struct
     Hashtbl.iter
       (fun dir f -> if String.is_prefix ~affix:dir file then f file)
       t.watches
-  (* |> Eio.Fiber.all *)
 
-  let mkdir _ = ()
+  let mkdir ~io:() _ = ()
 
-  let remove_file ?lock file =
-    with_lock lock (fun () -> Hashtbl.remove t.files file)
+  let remove_file ~io ?lock file =
+    with_lock ~io lock (fun () -> Hashtbl.remove t.files file)
 
-  let rec_files (_, dir) =
+  let rec_files ~io:() dir =
     Hashtbl.fold
-      (fun ((_, k) as v) _ acc ->
-        if String.is_prefix ~affix:dir k then v :: acc else acc)
+      (fun file _ acc ->
+        if String.is_prefix ~affix:dir file then file :: acc else acc)
       t.files []
 
-  let file_exists file = Hashtbl.mem t.files file
+  let file_exists ~io:() file = Hashtbl.mem t.files file
 
-  let read_file file =
+  let read_file ~io:() file =
     try
       let buf = Hashtbl.find t.files file in
       Some buf
     with Not_found -> None
 
-  let write_file ?temp_dir:_ ?lock ((_, file) as f) v =
-    let () = with_lock lock (fun () -> Hashtbl.replace t.files f v) in
+  let write_file ~io ~temp_dir:_ ?(lock : lock option) file v =
+    let () = with_lock ~io lock (fun () -> Hashtbl.replace t.files file v) in
     notify file
 
   let equal x y =
@@ -394,7 +406,7 @@ module IO_mem = struct
     | Some x, Some y -> String.equal x y
     | _ -> false
 
-  let test_and_set_file ?temp_dir:_ ~lock file ~test ~set =
+  let test_and_set_file ~io ~temp_dir:_ ~lock file ~test ~set =
     let f () =
       let old = try Some (Hashtbl.find t.files file) with Not_found -> None in
       let b =
@@ -408,10 +420,10 @@ module IO_mem = struct
               Hashtbl.replace t.files file v;
               true
       in
-      let () = if b then notify (snd file) in
+      let () = if b then notify file in
       b
     in
-    with_lock (Some lock) f
+    with_lock ~io (Some lock) f
 
   let clear () =
     Hashtbl.clear t.files;
@@ -423,17 +435,3 @@ module Maker_is_a_maker : Irmin.Maker = Maker (IO_mem)
 
 (* Enforce that {!KV} is a sub-type of {!Irmin.KV_maker}. *)
 module KV_is_a_KV : Irmin.KV_maker = KV (IO_mem)
-
-let run (fs : Fs.dir_ty Path.t) fn =
-  Switch.run @@ fun sw ->
-  Irmin.Backend.Watch.set_watch_switch sw;
-  let open Effect.Deep in
-  try_with fn ()
-    {
-      effc =
-        (fun (type a) (e : a Effect.t) ->
-          match e with
-          | Irmin.Backend.Conf.Env.Fs ->
-              Some (fun (k : (a, _) continuation) -> continue k fs)
-          | _ -> None);
-    }
diff --git a/src/irmin-fs/irmin_fs.mli b/src/irmin-fs/irmin_fs.mli
index a463246c6b..da2242530a 100644
--- a/src/irmin-fs/irmin_fs.mli
+++ b/src/irmin-fs/irmin_fs.mli
@@ -33,37 +33,43 @@ val config : string -> Irmin.config
 module type IO = sig
   (** {1 File-system abstractions} *)
 
-  type path = Eio.Fs.dir_ty Eio.Path.t
+  type io
+
+  val io_of_config : Irmin.config -> io
+
+  type path = string
   (** The type for paths. *)
 
   (** {2 Read operations} *)
 
-  val rec_files : path -> path list
+  val rec_files : io:io -> path -> path list
   (** [rec_files dir] is the list of files recursively present in [dir] and all
       of its sub-directories. Return filenames prefixed by [dir]. *)
 
-  val file_exists : path -> bool
+  val file_exists : io:io -> path -> bool
   (** [file_exist f] is true if [f] exists. *)
 
-  val read_file : path -> string option
+  val read_file : io:io -> path -> string option
   (** Read the contents of a file using mmap. *)
 
   (** {2 Write Operations} *)
 
-  val mkdir : path -> unit
+  val mkdir : io:io -> path -> unit
   (** Create a directory. *)
 
   type lock
   (** The type for file locks. *)
 
-  val lock_file : path -> lock
+  val lock_file : io:io -> path -> lock
   (** [lock_file f] is the lock associated to the file [f]. *)
 
-  val write_file : ?temp_dir:path -> ?lock:lock -> path -> string -> unit
+  val write_file :
+    io:io -> temp_dir:path -> ?lock:lock -> path -> string -> unit
   (** Atomic writes. *)
 
   val test_and_set_file :
-    ?temp_dir:path ->
+    io:io ->
+    temp_dir:path ->
     lock:lock ->
     path ->
     test:string option ->
@@ -71,7 +77,7 @@ module type IO = sig
     bool
   (** Test and set. *)
 
-  val remove_file : ?lock:lock -> path -> unit
+  val remove_file : io:io -> ?lock:lock -> path -> unit
   (** Remove a file or directory (even if non-empty). *)
 end
 
@@ -83,10 +89,9 @@ module KV (IO : IO) : Irmin.KV_maker with type info = Irmin.Info.default
 (** {2 Advanced configuration} *)
 
 module type Config = sig
-  open Eio
   (** Same as [Config] but gives more control on the file hierarchy. *)
 
-  val dir : Fs.dir_ty Path.t -> Fs.dir_ty Path.t
+  val dir : string -> string
   (** [dir root] is the sub-directory to look for the keys. *)
 
   val file_of_key : string -> string
@@ -108,5 +113,3 @@ module IO_mem : sig
   val clear : unit -> unit
   val set_listen_hook : unit -> unit
 end
-
-val run : Eio.Fs.dir_ty Eio.Path.t -> (unit -> 'a) -> 'a
diff --git a/src/irmin-fs/unix/dune b/src/irmin-fs/unix/dune
index b8cb6dd1d8..324d06cd44 100644
--- a/src/irmin-fs/unix/dune
+++ b/src/irmin-fs/unix/dune
@@ -1,7 +1,7 @@
 (library
  (public_name irmin-fs.unix)
  (name irmin_fs_unix)
- (libraries irmin-fs irmin.unix lwt eio eio.unix)
+ (libraries irmin-fs irmin.unix eio eio.unix)
  (preprocess
   (pps ppx_irmin.internal))
  (instrumentation
diff --git a/src/irmin-fs/unix/eio_pool.ml b/src/irmin-fs/unix/eio_pool.ml
index e32c122638..1c0b75cdab 100644
--- a/src/irmin-fs/unix/eio_pool.ml
+++ b/src/irmin-fs/unix/eio_pool.ml
@@ -103,8 +103,7 @@ let acquire p =
       (* Limit reached: wait for a free one. *)
       let promise, resolver = Promise.create () in
       Stream.add p.waiters resolver;
-      validate_and_return p (Promise.await_exn promise)
-      (* (Lwt.add_task_r [@ocaml.warning "-3"]) p.waiters >>= validate_and_return p *))
+      validate_and_return p (Promise.await_exn promise))
   else
     (* Take the first free member and validate it. *)
     let c = Queue.take p.list in
diff --git a/src/irmin-fs/unix/irmin_fs_unix.ml b/src/irmin-fs/unix/irmin_fs_unix.ml
index ef7253ad7b..9e19cde381 100644
--- a/src/irmin-fs/unix/irmin_fs_unix.ml
+++ b/src/irmin-fs/unix/irmin_fs_unix.ml
@@ -14,6 +14,7 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  *)
 
+module Conf = Irmin.Backend.Conf
 include Irmin.Export_for_backends
 open Eio
 
@@ -21,9 +22,51 @@ let src = Logs.Src.create "fs.unix" ~doc:"logs fs unix events"
 
 module Log = (val Logs.src_log src : Logs.LOG)
 
+type fs = Eio.Fs.dir_ty Eio.Path.t
+type clock = float Eio.Time.clock_ty Eio.Time.clock
+type io = { fs : fs; clock : clock }
+
+let fs_typ : fs Conf.Typ.t = Conf.Typ.create ()
+let clock_typ : clock Conf.Typ.t = Conf.Typ.create ()
+
+let spec ~path:fs ~clock =
+  let spec = Conf.Spec.v "irmin-fs.unix" in
+  let fs = (fs :> fs) in
+  let _fs_key =
+    let to_string fs = Eio.Path.native_exn fs in
+    let of_string str = Ok Eio.Path.(fs / str) in
+    let of_json_string str =
+      match Irmin.Type.(of_json_string string) str with
+      | Ok str -> Ok Eio.Path.(fs / str)
+      | Error e -> Error e
+    in
+    Conf.key' ~typ:fs_typ ~spec ~typename:"_ Eio.Path.t" ~to_string ~of_string
+      ~of_json_string "fs" fs
+  in
+  let clock = (clock :> clock) in
+  let _clock_key =
+    let to_string _ = "Eio.Time.clock" in
+    let of_string _ = Ok clock in
+    let of_json_string _ = Ok clock in
+    Conf.key' ~typ:clock_typ ~spec ~typename:"_ Eio.Time.clock" ~to_string
+      ~of_string ~of_json_string "clock" clock
+  in
+  spec
+
+let conf ~path ~clock = Conf.empty (spec ~path ~clock)
+
 module IO = struct
+  type nonrec io = io
+
+  let io_of_config conf =
+    {
+      fs = Conf.find_key conf "fs" fs_typ;
+      clock = Conf.find_key conf "clock" clock_typ;
+    }
+
+  type path = string
+
   let mkdir_pool = Eio_pool.create 1 (fun () -> ())
-  let mmap_threshold = 4096
 
   (* Files smaller than this are loaded using [read].  Use of mmap is
      necessary to handle packfiles efficiently. Since these are stored
@@ -37,66 +80,41 @@ module IO = struct
   (* Pool of opened files *)
   let openfile_pool = Eio_pool.create 200 (fun () -> ())
 
-  let protect_unix_exn = function
-    | Unix.Unix_error _ as e -> raise (Failure (Printexc.to_string e))
-    | e -> raise e
-
-  let ignore_enoent = function
-    | Unix.Unix_error (Unix.ENOENT, _, _) -> ()
-    | e -> raise e
-
-  let protect f x = try f x with exn -> protect_unix_exn exn
-  let safe f x = try f x with exn -> ignore_enoent exn
-
   let mkdir dirname =
-    let rec aux ((_, path) as dir) =
-      if Sys.file_exists path && Sys.is_directory path then ()
-      else (
-        if Sys.file_exists path then (
-          [%log.debug "%s already exists but is a file, removing." path];
-          safe Path.unlink dir);
-        let parent = (fst dir, Filename.dirname @@ snd dir) in
-        aux parent;
-        [%log.debug "mkdir %s" path];
-        protect (Path.mkdir ~perm:0o755) dir)
-    in
-    (* TODO: Pool *)
-    Eio_pool.use mkdir_pool (fun () -> aux dirname)
+    Eio_pool.use mkdir_pool (fun () ->
+        Eio.Path.mkdirs ~exists_ok:true ~perm:0o755 dirname)
 
-  let file_exists (_, f) =
-    try Sys.file_exists f with
-    (* See https://github.com/ocsigen/lwt/issues/316 *)
-    | Unix.Unix_error (Unix.ENOTDIR, _, _) -> false
-    | e -> raise e
+  let mkdir_parent file =
+    match Eio.Path.split file with
+    | None -> ()
+    | Some (parent, _) -> mkdir parent
+
+  let file_exists ~io:{ fs; _ } filename = Eio.Path.(is_file (fs / filename))
 
   module Lock = struct
-    let is_stale max_age file =
+    let is_stale ~io:{ clock; _ } max_age file =
       try
-        let s = Eio_unix.run_in_systhread (fun () -> Unix.stat file) in
-        if s.Unix.st_mtime < 1.0 (* ??? *) then false
-        else Unix.gettimeofday () -. s.Unix.st_mtime > max_age
-      with
-      | Unix.Unix_error (Unix.ENOENT, _, _) -> false
-      | e -> raise e
+        let { Eio.File.Stat.mtime; _ } = Eio.Path.stat ~follow:false file in
+        if mtime < 1.0 (* ??? *) then false
+        else Eio.Time.now clock -. mtime > max_age
+      with Eio.Io (Eio.Fs.E (Not_found _), _) -> false
 
     let unlock file = Path.unlink file
 
-    let lock ?(max_age = 10. *. 60. (* 10 minutes *)) ?(sleep = 0.001)
-        ((_, file) as fcap) =
+    let lock ~io ?(max_age = 10. *. 60. (* 10 minutes *)) ?(sleep = 0.001) file
+        =
       let rec aux i =
-        [%log.debug "lock %s %d" file i];
-        let is_stale = is_stale max_age file in
-        if is_stale then (
-          [%log.err "%s is stale, removing it." file];
-          unlock fcap;
+        [%log.debug "lock %a %d" Eio.Path.pp file i];
+        if is_stale ~io max_age file then (
+          [%log.err "%a is stale, removing it." Eio.Path.pp file];
+          unlock file;
           aux 1)
         else
           let create () =
             let pid = Unix.getpid () in
-            let parent = (fst fcap, Filename.dirname file) in
-            mkdir parent;
+            mkdir_parent file;
             Switch.run @@ fun sw ->
-            let flow = Path.open_out ~sw fcap ~create:(`Exclusive 0o600) in
+            let flow = Path.open_out ~sw file ~create:(`Exclusive 0o600) in
             Flow.copy_string (string_of_int pid) flow
           in
           try create () with
@@ -107,180 +125,131 @@ module IO = struct
                      (let i = float i in
                       i *. i)
               in
-              Eio_unix.sleep (sleep *. backoff);
+              Eio.Time.sleep io.clock (sleep *. backoff);
               aux (i + 1)
           | e -> raise e
       in
       aux 1
 
-    let with_lock file fn =
+    let with_lock ~io file fn =
       match file with
       | None -> fn ()
       | Some f ->
-          lock f;
+          lock ~io f;
           Fun.protect fn ~finally:(fun () -> unlock f)
   end
 
-  type path = Eio.Fs.dir_ty Eio.Path.t
-
   (* we use file locking *)
-  type lock = path
+  type lock = Eio.Fs.dir_ty Eio.Path.t
 
-  let lock_file x = x
-  let file_exists = file_exists
+  let lock_file ~io:{ fs; _ } x = Path.(fs / x)
 
-  let list_files kind ((_, dir) as v) =
-    if Sys.file_exists dir && Sys.is_directory dir then
-      let d = Path.read_dir v in
-      let d = List.sort String.compare d in
-      let d = List.map (Path.( / ) v) d in
+  let list_files kind dir =
+    if Eio.Path.is_directory dir then
+      let d = Path.read_dir dir in
+      let d = List.map (Path.( / ) dir) d in
       let d = List.filter kind d in
       d
     else []
 
-  let directories dir =
-    list_files
-      (fun (_, f) -> try Sys.is_directory f with Sys_error _ -> false)
-      dir
-
-  let files dir =
-    list_files
-      (fun (_, f) -> try not (Sys.is_directory f) with Sys_error _ -> false)
-      dir
+  let directories dir = list_files Eio.Path.is_directory dir
+  let files dir = list_files Eio.Path.is_file dir
 
   let write_string fd b =
     match String.length b with 0 -> () | _len -> Flow.copy_string b fd
 
   let _delays = Array.init 20 (fun i -> 0.1 *. (float i ** 2.))
+  let remove_dir dir = Eio.Path.rmtree dir
 
-  let command fmt =
-    Printf.ksprintf
-      (fun str ->
-        [%log.debug "[exec] %s" str];
-        let i = Sys.command str in
-        if i <> 0 then [%log.debug "[exec] error %d" i])
-      fmt
-
-  let remove_dir dir =
-    if Sys.os_type = "Win32" then command "cmd /d /v:off /c rd /s /q %S" dir
-    else command "rm -rf %S" dir
-
-  let remove_file ?lock ((_, file) as f) =
-    Lock.with_lock lock (fun () ->
-        try Path.unlink f with
-        (* On Windows, [EACCES] can also occur in an attempt to
-           rename a file or directory or to remove an existing
-           directory. *)
-        | Unix.Unix_error (Unix.EACCES, _, _)
-        | Unix.Unix_error (Unix.EISDIR, _, _)
-        | Eio.Io (Eio.Exn.X (Eio_unix.Unix_error (Unix.EACCES, _, _)), _)
-        | Eio.Io (Eio.Exn.X (Eio_unix.Unix_error (Unix.EISDIR, _, _)), _) ->
-            remove_dir file
-        | Unix.Unix_error (Unix.ENOENT, _, _)
-        | Eio.Io (Eio.Fs.E (Fs.Not_found _), _) ->
-            ()
-        | e -> raise e)
-
-  let rename tmp file = Path.rename tmp file
-
-  let with_write_file ?temp_dir file fn =
-    let () = match temp_dir with None -> () | Some d -> mkdir d in
-    let dir = (fst file, Filename.dirname @@ snd file) in
-    mkdir dir;
-    let temp_dir_path = Option.get temp_dir in
-    let temp_dir = snd temp_dir_path in
-    let file_f = snd file in
-    let tmp_f =
-      Filename.temp_file ~temp_dir (Filename.basename file_f) "write"
+  let remove_file ~io ?lock file =
+    Lock.with_lock ~io lock (fun () ->
+        let file = Path.(io.fs / file) in
+        if Path.is_directory file then remove_dir file
+        else
+          try Path.unlink file
+          with Eio.Io (Eio.Fs.E (Fs.Not_found _), _) -> ())
+
+  let temp_file ~temp_dir file suffix =
+    let basename =
+      match Eio.Path.split file with
+      | None -> "tmp"
+      | Some (_, basename) -> basename
+    in
+    let rec go i =
+      let tmp = Eio.Path.(temp_dir / (basename ^ string_of_int i ^ suffix)) in
+      if Eio.Path.kind ~follow:false tmp = `Not_found then tmp else go (i + 1)
     in
-    let tmp_name = Filename.basename tmp_f in
+    go 0
+
+  let with_write_file ~temp_dir file fn =
+    mkdir temp_dir;
+    mkdir_parent file;
+    let tmp_file = temp_file ~temp_dir file "write" in
     Eio_pool.use openfile_pool (fun () ->
-        [%log.debug
-          "Writing %s (%s) %s %s" file_f tmp_f (snd temp_dir_path) (snd file)];
-        Path.(
-          with_open_out ~create:(`Or_truncate 0o644) (temp_dir_path / tmp_name)
-            fn);
-        rename Path.(temp_dir_path / tmp_name) file)
+        [%log.debug "Writing %a (%a)" Eio.Path.pp file Eio.Path.pp tmp_file];
+        Path.(with_open_out ~create:(`Or_truncate 0o644) tmp_file fn);
+        Path.rename tmp_file file)
 
   let read_file_with_read file size =
-    (* let chunk_size = max 4096 (min size 0x100000) in *)
     let buf = Cstruct.create size in
-    (* let flags = [ Unix.O_RDONLY ] in
-       let perm = 0o0 in *)
-    (* let* fd = Lwt_unix.openfile file flags perm in *)
     Path.with_open_in file @@ fun flow ->
-    try
-      Flow.read_exact flow buf;
-      Cstruct.to_string buf
-    with End_of_file -> Cstruct.to_string buf
-
-  let read_file_with_mmap file =
-    let open Bigarray in
-    let fd = Unix.(openfile file [ O_RDONLY; O_NONBLOCK ] 0o644) in
-    let ba =
-      Unix.map_file fd char c_layout false [| -1 |]
-      |> Bigarray.array1_of_genarray
-    in
-    Unix.close fd;
+    Flow.read_exact flow buf;
+    Cstruct.to_string buf
 
-    (* XXX(samoht): ideally we should not do a copy here. *)
-    Bigstringaf.to_string ba
-
-  let read_file file =
-    let file_f = snd file in
+  let read_file ~io:{ fs; _ } file =
     try
+      let file = Path.(fs / file) in
       Eio_pool.use openfile_pool (fun () ->
-          [%log.debug "Reading %s" file_f];
-          let stats = Unix.stat file_f in
-          let size = stats.Unix.st_size in
-          let buf =
-            if size >= mmap_threshold then read_file_with_mmap file_f
-            else read_file_with_read file size
-          in
+          [%log.debug "Reading %a" Eio.Path.pp file];
+          let { Eio.File.Stat.size; _ } = Eio.Path.stat ~follow:false file in
+          let size = Optint.Int63.to_int size in
+          let buf = read_file_with_read file size in
           Some buf)
-    with
-    | Unix.Unix_error _ | Sys_error _ -> None
-    | e -> raise e
+    with Eio.Io _ -> None
 
-  let write_file ?temp_dir ?lock file b =
+  let write_file ~io ~temp_dir ?(lock : lock option) file b =
+    let file = Path.(io.fs / file) in
+    let temp_dir = Path.(io.fs / temp_dir) in
     let write () =
-      with_write_file file ?temp_dir (fun fd -> write_string fd b)
+      with_write_file file ~temp_dir (fun fd -> write_string fd b)
     in
-    Lock.with_lock lock (fun () ->
-        try write () with
-        | Unix.Unix_error (Unix.EISDIR, _, _) ->
-            remove_dir (snd file);
-            write ()
-        | e -> raise e)
-
-  let test_and_set_file ?temp_dir ~lock file ~test ~set =
-    Lock.with_lock (Some lock) (fun () ->
-        let v = read_file file in
+    Lock.with_lock ~io lock (fun () ->
+        if Path.is_directory file then remove_dir file;
+        write ())
+
+  let test_and_set_file ~io ~temp_dir ~lock file ~test ~set =
+    Lock.with_lock ~io (Some lock) (fun () ->
+        let v = read_file ~io file in
         let equal =
           match (test, v) with
           | None, None -> true
-          | Some x, Some y -> x = y (* TODO *)
+          | Some x, Some y -> String.equal x y
           | _ -> false
         in
         if not equal then false
         else
           let () =
             match set with
-            | None -> remove_file file
-            | Some v -> write_file ?temp_dir file v
+            | None -> remove_file ~io file
+            | Some v -> write_file ~io ~temp_dir file v
           in
           true)
 
-  let rec_files dir : Fs.dir_ty Path.t list =
+  let rec_files ~io:{ fs; _ } dir : path list =
+    let dir = Path.(fs / dir) in
     let rec aux accu dir =
       let ds = directories dir in
       let fs = files dir in
       List.fold_left aux (fs @ accu) ds
     in
-    aux [] dir
+    aux [] dir |> List.map snd
+
+  let mkdir ~io:{ fs; _ } dirname = mkdir Path.(fs / dirname)
 end
 
-module Append_only = Irmin_fs.Append_only (IO)
+module Append_only (K : Irmin.Type.S) (V : Irmin.Type.S) =
+  Irmin_fs.Append_only (IO) (K) (V)
+
 module Atomic_write = Irmin_fs.Atomic_write (IO)
 include Irmin_fs.Maker (IO)
 module KV = Irmin_fs.KV (IO)
diff --git a/src/irmin-fs/unix/irmin_fs_unix.mli b/src/irmin-fs/unix/irmin_fs_unix.mli
index bcfe077790..b75a48b0bb 100644
--- a/src/irmin-fs/unix/irmin_fs_unix.mli
+++ b/src/irmin-fs/unix/irmin_fs_unix.mli
@@ -28,3 +28,10 @@ module Maker_ext (Obj : Irmin_fs.Config) (Ref : Irmin_fs.Config) : Irmin.Maker
 (** {1 Common Unix utilities} *)
 
 include module type of Irmin_unix
+
+(** {1 Backend-specific config} *)
+
+val spec :
+  path:_ Eio.Path.t -> clock:_ Eio.Time.clock -> Irmin.Backend.Conf.Spec.t
+
+val conf : path:_ Eio.Path.t -> clock:_ Eio.Time.clock -> Irmin.Backend.Conf.t
diff --git a/src/irmin/conf.ml b/src/irmin/conf.ml
index d66e810a12..c694a1241d 100644
--- a/src/irmin/conf.ml
+++ b/src/irmin/conf.ml
@@ -16,6 +16,25 @@
  *)
 open! Import
 
+type (_, _) eq = Refl : ('a, 'a) eq
+
+module Typ = struct
+  type 'a s = ..
+  type 'a t = { s : 'a s; eq : 'b. 'b s -> ('a, 'b) eq option }
+
+  let create (type a) () : a t =
+    let open struct
+      type _ s += S : a s
+
+      let eq : type b. b s -> (a, b) eq option = function
+        | S -> Some Refl
+        | _ -> None
+    end in
+    { s = S; eq }
+
+  let equal a b = a.eq b.s
+end
+
 module Univ = struct
   type t = exn
 
@@ -31,8 +50,12 @@ type 'a key = {
   doc : string option;
   docv : string option;
   docs : string option;
-  ty : 'a Type.t;
+  typename : string;
+  to_string : 'a -> string;
+  of_string : string -> ('a, [ `Msg of string ]) result;
+  of_json_string : string -> ('a, [ `Msg of string ]) result;
   default : 'a;
+  typ : 'a Typ.t;
   to_univ : 'a -> Univ.t;
   of_univ : Univ.t -> 'a option;
 }
@@ -50,20 +73,9 @@ module Spec = struct
 
   type t = { name : string; mutable keys : k M.t }
 
-  let all = Hashtbl.create 8
-
-  let v name =
-    let keys = M.empty in
-    if Hashtbl.mem all name then
-      Fmt.failwith "Config spec already exists: %s" name;
-    let x = { name; keys } in
-    Hashtbl.replace all name x;
-    x
-
+  let v name = { name; keys = M.empty }
   let name { name; _ } = name
   let update spec name k = spec.keys <- M.add name k spec.keys
-  let list () = Hashtbl.to_seq_values all
-  let find name = Hashtbl.find_opt all name
   let find_key spec name = M.find_opt name spec.keys
   let keys spec = M.to_seq spec.keys |> Seq.map snd
   let clone { name; keys } = { name; keys }
@@ -87,7 +99,8 @@ type t = Spec.t * Univ.t M.t
 
 let spec = fst
 
-let key ?docs ?docv ?doc ?(allow_duplicate = false) ~spec name ty default =
+let key' ?docs ?docv ?doc ?(allow_duplicate = false) ?typ ~spec ~typename
+    ~to_string ~of_string ~of_json_string name default =
   let () =
     String.iter
       (function
@@ -99,16 +112,44 @@ let key ?docs ?docv ?doc ?(allow_duplicate = false) ~spec name ty default =
   | Some _ when allow_duplicate = false ->
       Fmt.invalid_arg "duplicate key: %s" name
   | _ ->
+      let typ = match typ with Some typ -> typ | None -> Typ.create () in
       let to_univ, of_univ = Univ.create () in
-      let k = { name; ty; default; to_univ; of_univ; doc; docv; docs } in
+      let k =
+        {
+          name;
+          to_string;
+          of_json_string;
+          of_string;
+          default;
+          typename;
+          typ;
+          to_univ;
+          of_univ;
+          doc;
+          docv;
+          docs;
+        }
+      in
       Spec.update spec name (K k);
       k
 
+let key ?docs ?docv ?doc ?allow_duplicate ?typ ~spec name ty default =
+  let to_string = Type.to_string ty in
+  let typename =
+    Fmt.str "%a" Type.pp_ty ty |> Astring.String.filter (fun c -> c <> '\n')
+  in
+  let of_string = Type.of_string ty in
+  let of_json_string = Type.of_json_string ty in
+  key' ?docs ?docv ?doc ?allow_duplicate ?typ ~spec ~typename ~to_string
+    ~of_json_string ~of_string name default
+
 let name t = t.name
 let doc t = t.doc
 let docv t = t.docv
 let docs t = t.docs
-let ty t = t.ty
+let typename t = t.typename
+let of_string t = t.of_string
+let of_json_string t = t.of_json_string
 let default t = t.default
 let empty spec = (spec, M.empty)
 let singleton spec k v = (spec, M.singleton (K k) (k.to_univ v))
@@ -143,6 +184,15 @@ let get (_, d) k =
     | None -> raise Not_found
   with Not_found -> k.default
 
+let find_key : type a. t -> string -> a Typ.t -> a =
+ fun ((spec, _) as t) name typ ->
+  match Spec.find_key spec name with
+  | Some (K k) -> (
+      match Typ.equal k.typ typ with
+      | Some Refl -> get t k
+      | None -> raise Not_found)
+  | None -> raise Not_found
+
 let keys (_, conf) = M.to_seq conf |> Seq.map (fun (k, _) -> k)
 let with_spec (_, conf) spec = (spec, conf)
 
@@ -152,7 +202,7 @@ let to_strings (_, conf) =
   |> Seq.map (fun (K k, v) ->
          ( k.name,
            match k.of_univ v with
-           | Some v -> Type.to_string k.ty v
+           | Some v -> k.to_string v
            | None -> assert false ))
 
 let pp ppf t =
@@ -177,13 +227,4 @@ let find_root (spec, d) : string option =
   | None -> None
   | Some (K k) -> (
       let v = find (spec, d) k in
-      match v with None -> None | Some v -> Some (Type.to_string k.ty v))
-
-module Env = struct
-  type _ Effect.t +=
-    | Fs : Eio.Fs.dir_ty Eio.Path.t Effect.t
-    | Net : _ Eio.Net.t Effect.t
-
-  let fs () = Effect.perform Fs
-  let net () = Effect.perform Net
-end
+      match v with None -> None | Some v -> Some (k.to_string v))
diff --git a/src/irmin/conf.mli b/src/irmin/conf.mli
index c312c0b6d1..533d277bb8 100644
--- a/src/irmin/conf.mli
+++ b/src/irmin/conf.mli
@@ -36,12 +36,6 @@ module Spec : sig
   val name : t -> string
   (** [name spec] is the name associated with a config spec *)
 
-  val list : unit -> t Seq.t
-  (** [list ()] is a sequence containing all available config specs *)
-
-  val find : string -> t option
-  (** [find name] is the config spec associated with [name] if available *)
-
   val find_key : t -> string -> k option
   (** [find_key spec k] is the key associated with the name [k] in [spec] *)
 
@@ -55,11 +49,18 @@ module Spec : sig
       the specs in [b] joined by hyphens. *)
 end
 
+module Typ : sig
+  type 'a t
+
+  val create : unit -> 'a t
+end
+
 val key :
   ?docs:string ->
   ?docv:string ->
   ?doc:string ->
   ?allow_duplicate:bool ->
+  ?typ:'a Typ.t ->
   spec:Spec.t ->
   string ->
   'a Type.t ->
@@ -83,11 +84,36 @@ val key :
       if [allow_duplicate] is [false] (the default) and [name] has already been
       used to create a key *)
 
+val key' :
+  ?docs:string ->
+  ?docv:string ->
+  ?doc:string ->
+  ?allow_duplicate:bool ->
+  ?typ:'a Typ.t ->
+  spec:Spec.t ->
+  typename:string ->
+  to_string:('a -> string) ->
+  of_string:(string -> ('a, [ `Msg of string ]) result) ->
+  of_json_string:(string -> ('a, [ `Msg of string ]) result) ->
+  string ->
+  'a ->
+  'a key
+(** Same as {!key} for types that don't implement [Type.t] but can be serialized
+    with [to_string], and deserialized with either [of_string] or
+    [of_json_string]. The [typename] is the user-readable description of the
+    type, in case of dynamic type errors. *)
+
 val name : 'a key -> string
 (** The key name. *)
 
-val ty : 'a key -> 'a Type.t
-(** [tc k] is [k]'s converter. *)
+val typename : 'a key -> string
+(** [typename k] is the type name of [k]'s values. *)
+
+val of_string : 'a key -> string -> ('a, [ `Msg of string ]) result
+(** [of_string k] is the parser of [k]'s values. *)
+
+val of_json_string : 'a key -> string -> ('a, [ `Msg of string ]) result
+(** [of_json_string k] is the json parser of [k]'s values. *)
 
 val default : 'a key -> 'a
 (** [default k] is [k]'s default value. *)
@@ -154,6 +180,10 @@ val keys : t -> k Seq.t
 val with_spec : t -> Spec.t -> t
 (** [with_spec t s] is the config [t] with spec [s] *)
 
+val find_key : t -> string -> 'a Typ.t -> 'a
+(** [find_key t name typ] returns the value associated with [name] in the config
+    [t]. *)
+
 val verify : t -> t
 (** [verify t] is an identity function that ensures all keys match the spec
 
@@ -166,12 +196,3 @@ val uri : Uri.t Type.t
 
 val find_root : t -> string option
 (** [find_root c] is [root]'s mapping in [c], if any. *)
-
-module Env : sig
-  type _ Effect.t +=
-    | Fs : Eio.Fs.dir_ty Eio.Path.t Effect.t
-    | Net : _ Eio.Net.t Effect.t
-
-  val fs : unit -> Eio.Fs.dir_ty Eio.Path.t
-  val net : unit -> _ Eio.Net.t
-end
diff --git a/src/libirmin/config.ml b/src/libirmin/config.ml
index 29fab1e0d6..50a87aeec5 100644
--- a/src/libirmin/config.ml
+++ b/src/libirmin/config.ml
@@ -40,10 +40,11 @@ module Make (I : Cstubs_inverted.INTERNAL) = struct
     fn "config_pack"
       (string_opt @-> string_opt @-> returning config)
       (fun hash contents ->
+        run_env @@ fun env ->
         try
           let hash = Option.map Irmin_cli.Resolver.Hash.find hash in
           let c : config =
-            Irmin_cli.Resolver.load_config ~store:"pack" ?hash ?contents ()
+            Irmin_cli.Resolver.load_config ~env ~store:"pack" ?hash ?contents ()
           in
           Root.create_config c
         with _ -> null config)
@@ -52,8 +53,11 @@ module Make (I : Cstubs_inverted.INTERNAL) = struct
     fn "config_tezos"
       (void @-> returning config)
       (fun () ->
+        run_env @@ fun env ->
         try
-          let c : config = Irmin_cli.Resolver.load_config ~store:"tezos" () in
+          let c : config =
+            Irmin_cli.Resolver.load_config ~env ~store:"tezos" ()
+          in
           Root.create_config c
         with _ -> null config)
 
@@ -61,8 +65,11 @@ module Make (I : Cstubs_inverted.INTERNAL) = struct
     fn "config_git"
       (string_opt @-> returning config)
       (fun contents ->
+        run_env @@ fun env ->
         try
-          let c = Irmin_cli.Resolver.load_config ~store:"git" ?contents () in
+          let c =
+            Irmin_cli.Resolver.load_config ~env ~store:"git" ?contents ()
+          in
           Root.create_config c
         with _ -> null config)
 
@@ -70,9 +77,10 @@ module Make (I : Cstubs_inverted.INTERNAL) = struct
     fn "config_git_mem"
       (string_opt @-> returning config)
       (fun contents ->
+        run_env @@ fun env ->
         try
           let c =
-            Irmin_cli.Resolver.load_config ~store:"git-mem" ?contents ()
+            Irmin_cli.Resolver.load_config ~env ~store:"git-mem" ?contents ()
           in
           Root.create_config c
         with _ -> null config)
@@ -81,10 +89,11 @@ module Make (I : Cstubs_inverted.INTERNAL) = struct
     fn "config_fs"
       (string_opt @-> string_opt @-> returning config)
       (fun hash contents ->
+        run_env @@ fun env ->
         try
           let hash = Option.map Irmin_cli.Resolver.Hash.find hash in
           let c =
-            Irmin_cli.Resolver.load_config ~store:"irf" ?hash ?contents ()
+            Irmin_cli.Resolver.load_config ~env ~store:"irf" ?hash ?contents ()
           in
           Root.create_config c
         with _ -> null config)
@@ -93,10 +102,11 @@ module Make (I : Cstubs_inverted.INTERNAL) = struct
     fn "config_mem"
       (string_opt @-> string_opt @-> returning config)
       (fun hash contents ->
+        run_env @@ fun env ->
         try
           let hash = Option.map Irmin_cli.Resolver.Hash.find hash in
           let c =
-            Irmin_cli.Resolver.load_config ~store:"mem" ?hash ?contents ()
+            Irmin_cli.Resolver.load_config ~env ~store:"mem" ?hash ?contents ()
           in
           Root.create_config c
         with _ -> null config)
@@ -116,7 +126,7 @@ module Make (I : Cstubs_inverted.INTERNAL) = struct
             | None -> (false, config)
             | Some (Irmin.Backend.Conf.K k) ->
                 let t : a Irmin.Type.t = Root.get_ty ty in
-                if type_name t <> type_name (Irmin.Backend.Conf.ty k) then
+                if type_name t <> Irmin.Backend.Conf.typename k then
                   (false, config)
                 else
                   let value = Root.get_value value in
@@ -139,8 +149,7 @@ module Make (I : Cstubs_inverted.INTERNAL) = struct
             | None -> (false, config)
             | Some (Irmin.Backend.Conf.K k) ->
                 let path =
-                  Irmin.Type.of_string (Irmin.Backend.Conf.ty k) path
-                  |> Result.get_ok
+                  Irmin.Backend.Conf.of_string k path |> Result.get_ok
                 in
                 (true, Irmin.Backend.Conf.add config k path)
           in
diff --git a/src/libirmin/util.ml b/src/libirmin/util.ml
index 3b0ad52b31..e2ab02c80c 100644
--- a/src/libirmin/util.ml
+++ b/src/libirmin/util.ml
@@ -43,9 +43,12 @@ module Make (I : Cstubs_inverted.INTERNAL) = struct
 
   let fn name t f = I.internal ~runtime_lock:false ("irmin_" ^ name) t f
 
-  let run fn =
+  let run_env fn =
     Eio_main.run @@ fun env ->
-    Lwt_eio.with_event_loop ~clock:env#clock @@ fun _ -> fn ()
+    Lwt_eio.with_event_loop ~clock:env#clock @@ fun () ->
+    fn (env :> Irmin_cli.eio)
+
+  let run fn = run_env (fun _ -> fn ())
 
   module Root = struct
     let to_voidp t x = Ctypes.coerce t (ptr void) x
diff --git a/test/irmin-cli/test.ml b/test/irmin-cli/test.ml
index 01123ad540..d04fbe4802 100644
--- a/test/irmin-cli/test.ml
+++ b/test/irmin-cli/test.ml
@@ -17,10 +17,10 @@
 include Irmin.Export_for_backends
 
 module Conf = struct
-  let test_config () =
+  let test_config ~env =
     let hash = Irmin_cli.Resolver.Hash.find "blake2b" in
     let _, cfg =
-      Irmin_cli.Resolver.load_config ~config_path:"test/irmin-cli/test.yml"
+      Irmin_cli.Resolver.load_config ~env ~config_path:"test/irmin-cli/test.yml"
         ~store:"pack" ~contents:"string" ~hash ()
     in
     let spec = Irmin.Backend.Conf.spec cfg in
@@ -34,8 +34,11 @@ module Conf = struct
     Alcotest.(check int) "index-log-size" 1234 index_log_size;
     Alcotest.(check bool) "fresh" true fresh
 
-  let misc : unit Alcotest.test_case list =
-    [ ("config", `Quick, fun () -> test_config ()) ]
+  let misc ~env : unit Alcotest.test_case list =
+    [ ("config", `Quick, fun () -> test_config ~env) ]
 end
 
-let () = Alcotest.run "irmin-cli" [ ("conf", Conf.misc) ]
+let () =
+  Eio_main.run @@ fun env ->
+  let env = (env :> Irmin_cli.eio) in
+  Alcotest.run "irmin-cli" [ ("conf", Conf.misc ~env) ]
diff --git a/test/irmin-cli/test_command_line.t b/test/irmin-cli/test_command_line.t
index cd99931ee0..3e11108b7b 100644
--- a/test/irmin-cli/test_command_line.t
+++ b/test/irmin-cli/test_command_line.t
@@ -94,3 +94,33 @@ Clone a local repo
   irmin: [WARNING] Updating the control file to [Used_non_minimal_indexing_strategy]. It won't be possible to GC this irmin-pack store anymore.
   $ irmin get --root ./cloned a/b/c
   123
+
+Show documentation
+  $ irmin
+  usage: irmin [--version]
+               [--help]
+               <command> [<args>]
+  
+  The most commonly used subcommands are:
+      init        Initialize a store.
+      get         Read the value associated with a key.
+      set         Update the value associated with a key.
+      remove      Delete a key.
+      list        List subdirectories.
+      tree        List the store contents.
+      clone       Copy a remote respository to a local store
+      fetch       Download objects and refs from another repository.
+      merge       Merge branches.
+      pull        Fetch and merge with another repository.
+      push        Update remote references along with associated objects.
+      snapshot    Return a snapshot for the current state of the database.
+      revert      Revert the contents of the store to a previous state.
+      watch       Get notifications when values change.
+      dot         Dump the contents of the store as a Graphviz file.
+      graphql     Run a graphql server.
+      server      Run irmin-server.
+      options     Get information about backend specific configuration options.
+      branches    List branches
+      log         List commits
+  
+  See `irmin help <command>` for more information on a specific command.
diff --git a/test/irmin-fs/test.ml b/test/irmin-fs/test.ml
index 17fb69d99d..7d7a322d71 100644
--- a/test/irmin-fs/test.ml
+++ b/test/irmin-fs/test.ml
@@ -15,7 +15,6 @@
  *)
 
 let () =
-  Eio_main.run @@ fun env ->
-  Irmin_fs.run env#fs @@ fun () ->
+  Eio_main.run @@ fun _env ->
   Irmin_test.Store.run "irmin-fs" ~slow:true ~misc:[] ~sleep:Eio_unix.sleep
     [ (`Quick, Test_fs.suite) ]
diff --git a/test/irmin-fs/test_fs_unix.ml b/test/irmin-fs/test_fs_unix.ml
index 2975f784f3..91d9d8a81d 100644
--- a/test/irmin-fs/test_fs_unix.ml
+++ b/test/irmin-fs/test_fs_unix.ml
@@ -19,7 +19,6 @@ let stats () =
   (stats.Irmin_watcher.watchdogs, Irmin.Backend.Watch.workers ())
 
 let test_db = Test_fs.test_db
-let config = Test_fs.config
 let store = Irmin_test.store (module Irmin_fs_unix) (module Irmin.Metadata.None)
 
 let clean_dirs config =
@@ -39,5 +38,6 @@ let clean ~config =
   clean_dirs config;
   Irmin.Backend.Watch.(set_listen_dir_hook none)
 
-let suite =
+let suite ~path ~clock =
+  let config = Irmin_fs_unix.conf ~path ~clock in
   Irmin_test.Suite.create ~name:"FS.UNIX" ~init ~store ~config ~clean ~stats ()
diff --git a/test/irmin-fs/test_unix.ml b/test/irmin-fs/test_unix.ml
index f312b9f3f4..adffd629d8 100644
--- a/test/irmin-fs/test_unix.ml
+++ b/test/irmin-fs/test_unix.ml
@@ -16,8 +16,9 @@
 
 let () =
   Eio_main.run @@ fun env ->
-  Irmin_fs.run env#fs @@ fun () ->
   Irmin_watcher.run @@ fun () ->
+  let path = Eio.Stdenv.cwd env in
+  let clock = Eio.Stdenv.clock env in
   Irmin_test.Store.run "irmin-fs.unix" ~slow:false ~sleep:Eio_unix.sleep
     ~misc:[]
-    [ (`Quick, Test_fs_unix.suite) ]
+    [ (`Quick, Test_fs_unix.suite ~path ~clock) ]
diff --git a/test/irmin/test_conf.ml b/test/irmin/test_conf.ml
index afcd08b7c9..e6aa40acd3 100644
--- a/test/irmin/test_conf.ml
+++ b/test/irmin/test_conf.ml
@@ -28,12 +28,6 @@ let test_conf () =
       (Invalid_argument "invalid config key: x") (fun () ->
         ignore (add (empty spec_b) x 1))
   in
-  let specs =
-    Spec.list () |> Seq.map Spec.name |> List.of_seq |> List.sort String.compare
-  in
-  let () =
-    Alcotest.(check (list string)) "Spec list" [ "a"; "b"; "mem" ] specs
-  in
   let keys =
     Spec.keys spec_a
     |> Seq.map (fun (K k) -> name k)