diff --git a/src/dummynet/process_monitor.py b/src/dummynet/process_monitor.py
index 5e12a8a..7fb6b71 100644
--- a/src/dummynet/process_monitor.py
+++ b/src/dummynet/process_monitor.py
@@ -53,7 +53,8 @@ def update_sudo_password():
     cached_sudo_password = os.environ.get("DUMMYNET_SUDO_PASSWD", None)
     if cached_sudo_password:
         # Environment variable was set, use it instead of asking for a password
-        cached_sudo_password += "\n"
+        if not cached_sudo_password.endswith("\n"):
+            cached_sudo_password += "\n"
         return
 
     prompt = f"\n[sudo] password for {getpass.getuser()}: "
@@ -79,53 +80,32 @@ class ProcessMonitor:
     class Poller:
         def __init__(self, log):
             self.poller = select.poll()
-            self.fds = {}
-            self.streams = {}
+            self.callbacks = {}
             self.log = log
 
-        def add_fd(self, stream, callback):
+        def add_fd(self, fd, callback):
             # Note that flags POLLHUP and POLLERR can be returned at any time
             # (even if were not asked for). So we don't need to explicitly
             # register for them.
-            self.poller.register(stream.fileno(), select.POLLIN)
+            self.poller.register(fd, select.POLLIN)
 
-            self.fds[stream.fileno()] = callback
-            self.streams[stream.fileno()] = stream
+            self.callbacks[fd] = callback
 
-            self.log.debug(f"Poller: register process fd {stream.fileno()}")
+            self.log.debug(f"Poller: register process fd {fd}")
 
         def del_fd(self, fd):
             self.poller.unregister(fd)
-            del self.fds[fd]
-            del self.streams[fd]
+            del self.callbacks[fd]
 
             self.log.debug(f"Poller: unregister process fd {fd}")
 
-        # def read_fd(self, fd):
-
-        #     self.log.error(f"Poller: reading from fd {fd}")
-        #     print(dir(self.streams[fd]))
-        #     data = os.read(fd, 4096)  # Read in chunks of 4096 bytes
-
-        #     self.log.error(f"Poller: read {len(data)}")
-
-        #     if not data:
-        #         return
-
-        #     self.log.debug(f"Poller: read {len(data)} bytes from fd {fd}")
-        #     self.log.debug(f"Poller: data: '{data}'")
-
-        #     # Call the callback
-        #     self.fds[fd](data.decode(encoding="utf-8", errors="replace"))
-
         def read_fd(self, fd):
             data = b""
             while True:
-                self.log.error(f"Poller: reading from fd {fd}")
                 chunk = os.read(fd, 4096)  # Read in chunks of 4096 bytes
-                self.log.error(f"Poller: read {len(chunk)}")
                 data += chunk
-                if not chunk or len(chunk) != 4096:
+                if len(chunk) < 4096:
+                    # If we read less than 4096 bytes, we are done
                     break
 
             if not data:
@@ -135,7 +115,7 @@ def read_fd(self, fd):
             self.log.debug(f"Poller: data: '{data}'")
 
             # Call the callback
-            self.fds[fd](data.decode(encoding="utf-8", errors="replace"))
+            self.callbacks[fd](data.decode(encoding="utf-8", errors="replace"))
 
         def poll(self, timeout):
             fds = self.poller.poll(timeout)
@@ -157,8 +137,7 @@ def poll(self, timeout):
                     self.del_fd(fd=fd)
 
         def wait_fd(self, fd):
-
-            while fd in self.fds:
+            while fd in self.callbacks:
                 self.poll(timeout=0.1)
 
     class Process:
@@ -190,6 +169,9 @@ def __init__(
 
             # Pipe possible sudo password to the process
             if sudo and (cached_sudo_password is not None):
+                assert cached_sudo_password.endswith(
+                    "\n"
+                )  # Ensure the password ends with a newline as otherwise sudo will hang
                 self.popen.stdin.write(cached_sudo_password)
                 self.popen.stdin.flush()
 
@@ -227,12 +209,12 @@ def stderr_callback(data):
 
             # Get the file descriptor
             poller.add_fd(
-                self.popen.stdout,
+                self.popen.stdout.fileno(),
                 stdout_callback,
             )
 
             poller.add_fd(
-                self.popen.stderr,
+                self.popen.stderr.fileno(),
                 stderr_callback,
             )