docs: extend FAQ
diff --git a/documentation/appendix.rst b/documentation/appendix.rst
index 5d8bae0..0710f6f 100644
--- a/documentation/appendix.rst
+++ b/documentation/appendix.rst
@@ -71,6 +71,14 @@
search path in :data:`serial.protocol_handler_packages`. This is possible
starting from pySerial V2.6.
+``Permission denied`` errors
+ On POSIX based systems, the user usually needs to be in a special group to
+ have access to serial ports.
+
+ On Debian based systems, serial ports are usually in the group ``dialout``,
+ so running ``sudo adduser $USER dialout`` (and logging-out and -in) enables
+ the user to use the port.
+
Related software
================