diff --git a/Cargo.toml b/Cargo.toml
index 4c82032..7c9a897 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -6,11 +6,11 @@ edition = "2018"
 build = "src/build.rs"
 
 [dependencies]
-users = "0.10.0"
+users = "0.11.0"
 regex = "1.0.1"
 futures = "0.3"
 async-trait = "0.1"
-tokio = { version = "0.2", features = ["process", "io-util", "rt-core", "macros", "sync"] }
+tokio = { version = "0.3", features = ["rt", "process", "io-util", "macros", "sync"] }
 once_cell = "1.4"
 
 [dev-dependencies]
diff --git a/src/async_utils.rs b/src/async_utils.rs
index 2c1196a..c656c53 100644
--- a/src/async_utils.rs
+++ b/src/async_utils.rs
@@ -6,11 +6,15 @@ use std::{
   thread,
   time::Duration,
 };
+use tokio::runtime::Builder;
 
 pub use async_trait::async_trait;
 
 pub fn run<F: Future>(future: F) -> F::Output {
-  tokio::runtime::Runtime::new().unwrap().block_on(future)
+  Builder::new_current_thread()
+    .build()
+    .unwrap()
+    .block_on(future)
 }
 pub use tokio::try_join;
 
diff --git a/src/builder.rs b/src/builder.rs
index 481096d..811c3f1 100644
--- a/src/builder.rs
+++ b/src/builder.rs
@@ -719,9 +719,7 @@ impl<D: Clone> ImplementationBuilder<MariaDbDatabase<D>> for DefaultBuilder {
 
 impl<D: Clone> ImplementationBuilder<PostgresqlDatabase<D>> for DefaultBuilder {
   type Prerequisites = ();
-  fn prerequisites(_: &PostgresqlDatabase<D>) -> Self::Prerequisites {
-    ()
-  }
+  fn prerequisites(_: &PostgresqlDatabase<D>) -> Self::Prerequisites {}
 
   type Implementation = (PostgreSQLDatabaseSymbol<'static, String, String, StdCommandRunner>,);
   fn create(
diff --git a/src/command_runner.rs b/src/command_runner.rs
index b69e7ee..0a64621 100644
--- a/src/command_runner.rs
+++ b/src/command_runner.rs
@@ -72,6 +72,7 @@ impl CommandRunner for StdCommandRunner {
       .expect("Failed to write to stdin");
     let res = child.wait_with_output().await;
     //println!("{:?}", res);
+    #[allow(clippy::let_and_return)]
     res
   }
 }
diff --git a/src/loggers.rs b/src/loggers.rs
index e5c8573..dcbd0e1 100644
--- a/src/loggers.rs
+++ b/src/loggers.rs
@@ -80,7 +80,7 @@ pub struct FilteringLogger<'a, L> {
 }
 
 impl<'a, L> FilteringLogger<'a, L> {
-  pub fn new(logger: &'a L, max_level: Level) -> Self {
+  pub const fn new(logger: &'a L, max_level: Level) -> Self {
     Self { logger, max_level }
   }
 }
@@ -104,6 +104,7 @@ pub struct StoringLogger {
 }
 
 impl StoringLogger {
+  #[must_use]
   pub fn new() -> Self {
     Self::default()
   }
diff --git a/src/setup/mod.rs b/src/setup/mod.rs
index cca4db8..a187a88 100644
--- a/src/setup/mod.rs
+++ b/src/setup/mod.rs
@@ -7,5 +7,6 @@ pub use symbol_runner::{
   SymbolRunner,
 };
 mod runnable;
+#[allow(clippy::module_inception)]
 mod setup;
 pub use setup::SetupFacade as Setup;
diff --git a/src/setup/runnable.rs b/src/setup/runnable.rs
index add3f49..4e3e087 100644
--- a/src/setup/runnable.rs
+++ b/src/setup/runnable.rs
@@ -16,6 +16,7 @@ pub trait Runnable {
 }
 
 #[async_trait(?Send)]
+#[allow(clippy::use_self)]
 impl<S> Runnable for S
 where
   Self: Symbol + Debug,
diff --git a/src/setup/setup.rs b/src/setup/setup.rs
index 842152b..472d52e 100644
--- a/src/setup/setup.rs
+++ b/src/setup/setup.rs
@@ -242,7 +242,9 @@ mod test {
     fn from_artifact(_from: ()) -> Self {
       Self
     }
+    #[allow(clippy::unused_unit)]
     fn into_artifact(self) -> () {
+      #[allow(clippy::unused_unit)]
       ()
     }
   }
diff --git a/src/storage.rs b/src/storage.rs
index a963414..aa4ce9d 100644
--- a/src/storage.rs
+++ b/src/storage.rs
@@ -14,6 +14,7 @@ pub trait Storage {
 pub struct SimpleStorage(PathBuf);
 
 impl SimpleStorage {
+  #[must_use]
   pub const fn new(base: PathBuf) -> Self {
     Self(base)
   }
diff --git a/src/symbols/dir.rs b/src/symbols/dir.rs
index f9fdacc..1a60af2 100644
--- a/src/symbols/dir.rs
+++ b/src/symbols/dir.rs
@@ -11,7 +11,7 @@ pub struct Dir<P> {
 }
 
 impl<P> Dir<P> {
-  pub fn new(path: P) -> Self {
+  pub const fn new(path: P) -> Self {
     Self { path }
   }
 }
diff --git a/src/symbols/file.rs b/src/symbols/file.rs
index edff275..a3763c1 100644
--- a/src/symbols/file.rs
+++ b/src/symbols/file.rs
@@ -12,7 +12,7 @@ pub struct File<D, C> {
 }
 
 impl<D, C> File<D, C> {
-  pub fn new(path: D, content: C) -> Self {
+  pub const fn new(path: D, content: C) -> Self {
     Self { path, content }
   }
 }
diff --git a/src/symbols/git/submodules.rs b/src/symbols/git/submodules.rs
index e35eabf..5413b8d 100644
--- a/src/symbols/git/submodules.rs
+++ b/src/symbols/git/submodules.rs
@@ -13,7 +13,7 @@ pub struct GitSubmodules<'a, P, C> {
 }
 
 impl<'a, P, C> GitSubmodules<'a, P, C> {
-  pub fn new(target: P, command_runner: &'a C) -> Self {
+  pub const fn new(target: P, command_runner: &'a C) -> Self {
     Self {
       target,
       command_runner,
diff --git a/src/symbols/mariadb/dump.rs b/src/symbols/mariadb/dump.rs
index 8276532..1b503fa 100644
--- a/src/symbols/mariadb/dump.rs
+++ b/src/symbols/mariadb/dump.rs
@@ -34,8 +34,8 @@ impl<'a, N, C: CommandRunner, S> Dump<'a, N, C, S> {
 impl<N: AsRef<str>, C: CommandRunner, S: Storage> Symbol for Dump<'_, N, C, S> {
   async fn target_reached(&self) -> Result<bool, Box<dyn Error>> {
     let dump_date = self.storage.recent_date()?;
-    let _modified_date = self.run_sql(&format!("select UNIX_TIMESTAMP(MAX(UPDATE_TIME)) from information_schema.tables WHERE table_schema = '{}'", self.db_name.as_ref())).await?;
-    let modified_date = _modified_date.trim_end();
+    let output = self.run_sql(&format!("select UNIX_TIMESTAMP(MAX(UPDATE_TIME)) from information_schema.tables WHERE table_schema = '{}'", self.db_name.as_ref())).await?;
+    let modified_date = output.trim_end();
     Ok(modified_date != "NULL" && u64::from_str(modified_date)? <= dump_date)
   }
 
diff --git a/src/symbols/systemd/user_session.rs b/src/symbols/systemd/user_session.rs
index 5de3342..1f41d46 100644
--- a/src/symbols/systemd/user_session.rs
+++ b/src/symbols/systemd/user_session.rs
@@ -11,7 +11,7 @@ pub struct UserSession<'a, U, C> {
 }
 
 impl<'a, U, C> UserSession<'a, U, C> {
-  pub fn new(user_name: U, command_runner: &'a C) -> Self {
+  pub const fn new(user_name: U, command_runner: &'a C) -> Self {
     Self {
       user_name,
       command_runner,
diff --git a/src/symbols/tls/csr.rs b/src/symbols/tls/csr.rs
index 3b35681..4af3683 100644
--- a/src/symbols/tls/csr.rs
+++ b/src/symbols/tls/csr.rs
@@ -14,7 +14,7 @@ pub struct Csr<C, D, K, P> {
 }
 
 impl<C, D, K, P> Csr<C, D, K, P> {
-  pub fn new(command_runner: C, domain: D, key_path: K, csr_path: P) -> Self {
+  pub const fn new(command_runner: C, domain: D, key_path: K, csr_path: P) -> Self {
     Self {
       command_runner,
       domain,
diff --git a/src/symbols/tls/key.rs b/src/symbols/tls/key.rs
index c5287c0..720d7ab 100644
--- a/src/symbols/tls/key.rs
+++ b/src/symbols/tls/key.rs
@@ -8,19 +8,17 @@ use std::path::Path;
 pub struct Key<C, P> {
   file_path: P,
   command_runner: C,
+  bytes: u32,
 }
 
 impl<C, P> Key<C, P> {
-  pub fn new(command_runner: C, file_path: P) -> Self {
+  pub const fn new(command_runner: C, file_path: P) -> Self {
     Self {
       file_path,
       command_runner,
+      bytes: 4096,
     }
   }
-
-  fn get_bytes(&self) -> u32 {
-    4096
-  }
 }
 
 #[async_trait(?Send)]
@@ -57,7 +55,7 @@ impl<C: CommandRunner, P: AsRef<Path>> Symbol for Key<C, P> {
           "genrsa",
           "-out",
           self.file_path.as_ref(),
-          self.get_bytes().to_string(),
+          self.bytes.to_string(),
         ],
       )
       .await
diff --git a/src/symbols/user.rs b/src/symbols/user.rs
index 3c67809..db784a7 100644
--- a/src/symbols/user.rs
+++ b/src/symbols/user.rs
@@ -15,7 +15,7 @@ pub struct User<U, C> {
 }
 
 impl<U, C> User<U, C> {
-  pub fn new(user_name: U, command_runner: C) -> Self {
+  pub const fn new(user_name: U, command_runner: C) -> Self {
     Self {
       user_name,
       command_runner,
diff --git a/src/templates/nginx/server.rs b/src/templates/nginx/server.rs
index fe7aa60..9f04bbd 100644
--- a/src/templates/nginx/server.rs
+++ b/src/templates/nginx/server.rs
@@ -1,6 +1,7 @@
 use std::fmt::Display;
 use std::path::Path;
 
+#[must_use]
 pub fn default_server<P: AsRef<Path>>(challenges_snippet_path: P) -> String {
   format!(
     "server {{
@@ -12,6 +13,7 @@ pub fn default_server<P: AsRef<Path>>(challenges_snippet_path: P) -> String {
   )
 }
 
+#[must_use]
 pub fn server_config<D: Display, C: AsRef<Path>, K: AsRef<Path>, T: Display, S: AsRef<Path>>(
   domain: D,
   cert_path: C,
@@ -53,6 +55,7 @@ server {{
   )
 }
 
+#[must_use]
 pub fn php_snippet<SOCKET: AsRef<Path>, STATIC: AsRef<Path>>(
   index: &'static str,
   socket_path: SOCKET,
@@ -71,6 +74,7 @@ pub fn php_snippet<SOCKET: AsRef<Path>, STATIC: AsRef<Path>>(
   )
 }
 
+#[must_use]
 pub fn redir_snippet(target: &str) -> String {
   format!(
     "location / {{
@@ -85,6 +89,7 @@ pub trait SocketSpec {
 }
 
 impl<T: AsRef<Path>> SocketSpec for T {
+  #[must_use]
   fn to_nginx(&self) -> String {
     format!("unix:{}:", self.as_ref().to_str().unwrap())
   }
@@ -94,17 +99,20 @@ impl<T: AsRef<Path>> SocketSpec for T {
 pub struct LocalTcpSocket(usize);
 
 impl LocalTcpSocket {
+  #[must_use]
   pub const fn new(x: usize) -> Self {
     Self(x)
   }
 }
 
 impl SocketSpec for LocalTcpSocket {
+  #[must_use]
   fn to_nginx(&self) -> String {
     format!("localhost:{}", self.0)
   }
 }
 
+#[must_use]
 pub fn proxy_snippet<S: SocketSpec, STATIC: AsRef<Path>>(
   socket_path: &S,
   static_path: STATIC,
@@ -125,6 +133,7 @@ pub fn proxy_snippet<S: SocketSpec, STATIC: AsRef<Path>>(
   )
 }
 
+#[must_use]
 pub fn static_snippet<S: AsRef<Path>>(static_path: S) -> String {
   format!(
     "root                    {};
@@ -134,6 +143,7 @@ pub fn static_snippet<S: AsRef<Path>>(static_path: S) -> String {
   )
 }
 
+#[must_use]
 pub fn dokuwiki_snippet() -> String {
   "
   location ~ /(data/|conf/|bin/|inc/|install.php) { deny all; }
@@ -149,6 +159,7 @@ pub fn dokuwiki_snippet() -> String {
   }".into()
 }
 
+#[must_use]
 pub fn nextcloud_snippet() -> String {
   "
   client_max_body_size 500M;