diff --git a/Cargo.lock b/Cargo.lock
index d15a8e4947..e90eb74431 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1413,6 +1413,7 @@ dependencies = [
  "once_cell",
  "percent-encoding",
  "pgp",
+ "port_check",
  "pretty_env_logger",
  "proptest",
  "qrcodegen",
@@ -4538,6 +4539,12 @@ dependencies = [
  "universal-hash",
 ]
 
+[[package]]
+name = "port_check"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f6519412c9e0d4be579b9f0618364d19cb434b324fc6ddb1b27b1e682c7105ed"
+
 [[package]]
 name = "portable-atomic"
 version = "0.3.15"
diff --git a/Cargo.toml b/Cargo.toml
index 37d72eea12..2e3e0a332e 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,7 +7,7 @@ license = "MPL-2.0"
 rust-version = "1.56"
 
 [profile.dev]
-#debug = 0
+debug = 0
 panic = 'abort'
 opt-level = 1
 
@@ -83,7 +83,8 @@ async_zip = { git = "https://github.com/dignifiedquire/rs-async-zip", branch = "
 iroh-share = { git = "https://github.com/n0-computer/iroh", branch = "main" }
 iroh-resolver = { git = "https://github.com/n0-computer/iroh", branch = "main", default-features = false }
 tempfile = "3"
-multibase = "0.9.1"
+multibase = "0.9"
+port_check = "0.1.5"
 
 [dev-dependencies]
 ansi_term = "0.12.0"
diff --git a/examples/repl/cmdline.rs b/examples/repl/cmdline.rs
index 9e32d70463..d7bc49005d 100644
--- a/examples/repl/cmdline.rs
+++ b/examples/repl/cmdline.rs
@@ -475,10 +475,12 @@ pub async fn cmdline(context: Context, line: &str, chat_id: &mut ChatId) -> Resu
                 Some(arg2.to_string()),
             )
             .await?;
-            println!("Exported to {}.", dir.to_string_lossy());
+            println!("Exported to {}.", dir.display());
         }
         "send-backup" => {
-            let dir = dirs::home_dir().unwrap_or_default();
+            let tdir = tempfile::TempDir::new()?;
+            let dir = tdir.path();
+            println!("Storing backup in: {} ", dir.display());
             let transfer = send_backup(&context, dir.as_ref(), Some(arg1.to_string())).await?;
             let ticket = transfer.ticket();
             let ticket_bytes = ticket.as_bytes();
diff --git a/foo-shm b/foo-shm
new file mode 100644
index 0000000000..85e14c8a0d
Binary files /dev/null and b/foo-shm differ
diff --git a/foo-wal b/foo-wal
new file mode 100644
index 0000000000..4454e4f4ea
Binary files /dev/null and b/foo-wal differ
diff --git a/src/imex.rs b/src/imex.rs
index 96727807ef..c666660fbf 100644
--- a/src/imex.rs
+++ b/src/imex.rs
@@ -5,7 +5,7 @@ use std::ffi::OsStr;
 use std::path::{Path, PathBuf};
 
 use ::pgp::types::KeyTrait;
-use anyhow::{bail, ensure, format_err, Context as _, Result};
+use anyhow::{anyhow, bail, ensure, format_err, Context as _, Result};
 use futures::{StreamExt, TryStreamExt};
 use futures_lite::FutureExt;
 use rand::{thread_rng, Rng};
@@ -107,6 +107,10 @@ pub async fn imex(
     res
 }
 
+/// Receives a backup, as sent from `send_backup`.
+///
+/// Only one receive-progress can run at the same time.
+/// To cancel a receive-progress, drop the future returned by this function.
 pub async fn receive_backup(
     context: &Context,
     ticket_bytes: Vec<u8>,
@@ -135,7 +139,7 @@ pub async fn receive_backup(
     res
 }
 
-pub async fn receive_backup_inner(
+async fn receive_backup_inner(
     context: &Context,
     ticket_bytes: Vec<u8>,
     passphrase: String,
@@ -153,11 +157,12 @@ pub async fn receive_backup_inner(
 
     let recv_dir = tempfile::tempdir().unwrap();
     let recv_db = recv_dir.path().join("db");
-    let port = 9991;
+    let port = port_check::free_local_port()
+        .ok_or_else(|| anyhow!("failed to find free local port to bind to"))?;
 
     let receiver = Receiver::new(port, &recv_db)
         .await
-        .context("failed to create sender")?;
+        .context("failed to create receiver")?;
     let mut receiver_transfer = receiver
         .transfer_from_ticket(&ticket)
         .await
@@ -200,9 +205,10 @@ pub async fn receive_backup_inner(
         let name = link.name.unwrap_or_default();
         let path = out.join(&name);
 
-        let mut file = tokio::fs::File::create(&path)
+        let file = tokio::fs::File::create(&path)
             .await
             .with_context(|| format!("create file: {}", path.display()))?;
+        let mut file = tokio::io::BufWriter::new(file);
         let mut content = file_content.pretty()?;
         tokio::io::copy(&mut content, &mut file)
             .await
@@ -232,6 +238,10 @@ pub async fn receive_backup_inner(
     Ok(())
 }
 
+/// Send a backup.
+///
+/// Only one send-progress can run at the same time.
+/// To cancel a send-progress, drop the future returned by this function.
 pub async fn send_backup(
     context: &Context,
     path: &Path,
@@ -832,7 +842,8 @@ async fn export_backup_iroh(
 
     match res {
         Ok(dir_builder) => {
-            let port = 9990;
+            let port = port_check::free_local_port()
+                .ok_or_else(|| anyhow!("failed to find free local port to bind to"))?;
             let sender = iroh_share::Sender::new(port, &sender_db_path).await?;
             let transfer = sender.transfer_from_dir_builder(dir_builder).await?;