diff --git a/src/Jobs.fs b/src/Jobs.fs
deleted file mode 100644
index 86bc152..0000000
--- a/src/Jobs.fs
+++ /dev/null
@@ -1,5 +0,0 @@
-module Bidello.Jobs
-
-open Bidello.Datatypes
-
-open NodaTime
diff --git a/src/Library.fs b/src/Library.fs
index c63f833..f48fa40 100644
--- a/src/Library.fs
+++ b/src/Library.fs
@@ -70,7 +70,6 @@ type Bidello(client: IClusterClient) =
                 let timeout = next_job_at - now |> _.TotalMilliseconds |> floor |> int32
                 // printfn $"Waking up in: {timeout}|{next_job_at}"
                 let! _wake_up = db |> Database.wait_notification timeout ct
-                // TODO: se il lavoro da fare, è già in esecuzione (e ancora non terminato, che fare?)
                 ()
         }
 
diff --git a/src/Shell.fs b/src/Shell.fs
new file mode 100644
index 0000000..9b8970e
--- /dev/null
+++ b/src/Shell.fs
@@ -0,0 +1,50 @@
+module Bidello.Shell
+
+open Sheller
+
+open FSharp.Control.LazyExtensions
+
+open Pentole.Path
+
+let private shell_ () =
+    let possible_shells = [
+        "/bin/sh"
+        "/bin/bash"
+        "/bin/dash"
+        "/bin/fish"
+        "/usr/bin/sh"
+        "/usr/bin/bash"
+        "/usr/bin/dash"
+        "/usr/bin/fish"
+    ]
+
+    let error = Error "Can't find the system shell. Check your system $PATH."
+    List.tryFind (fun sh -> sh |> Path.of_string |> Result.isOk) possible_shells
+    |> Option.map Ok |> Option.defaultValue error
+
+
+let shell = Lazy.Create shell_
+
+let which (executable: string) =
+    let run (shell: string) =
+        let rc = 
+            Builder
+                .UseShell(shell)
+                .UseExecutable("which")
+                .WithArgument(executable)
+                .UseNoThrow()
+                .ExecuteAsync ()
+                |> Async.AwaitTask
+                |> Async.RunSynchronously
+        if rc.ExitCode = 0 then
+            rc.StandardOutput
+            |> _.Trim()
+            |> Path.of_string
+        elif rc.ExitCode = 1 then
+            Error $"Can't find executable path for \"{executable}\"."
+        else
+            rc.StandardError
+            |> Error
+
+    shell.Value
+    |> Result.bind run
diff --git a/src/src.fsproj b/src/src.fsproj
index 081c662..03e87d2 100644
--- a/src/src.fsproj
+++ b/src/src.fsproj
@@ -13,13 +13,12 @@
     <Compile Include="Seq.fs" />
     <Compile Include="Result.fs" />
     <Compile Include="String.fs" />
-    <Compile Include="Which.fs" />
+    <Compile Include="Shell.fs" />
     <Compile Include="Datatypes.fs" />
     <Compile Include="Grains.fs" />
     <Compile Include="DatabaseMigrations.fs" />
     <Compile Include="Database.fs" />
     <Compile Include="Cron.fs" />
-    <Compile Include="Jobs.fs" />
     <Compile Include="Library.fs" />
   </ItemGroup>