Some small fixes

src/symbols/user.rs

@@ -1,7 +1,12 @@
 use crate::command_runner::CommandRunner;
 use crate::symbols::Symbol;
 use async_trait::async_trait;
+use once_cell::sync::Lazy;
 use std::error::Error;
+use tokio::sync::Semaphore;
+
+pub type Wait = Lazy<Semaphore>;
+static WAIT: Wait = Lazy::new(|| Semaphore::new(1));
 
 #[derive(Debug)]
 pub struct User<U, C> {
@@ -33,6 +38,9 @@ impl<U: AsRef<str>, C: CommandRunner> Symbol for User<U, C> {
   }
 
   async fn execute(&self) -> Result<(), Box<dyn Error>> {
+    // adduser is not reentrant because finding the next uid
+    // and creating the account is not an atomic operation
+    let wait = WAIT.acquire().await;
     self
       .command_runner
       .run_successfully(