Background

There are two main executables involved in starting a session:

Executable	Log File	Purpose
xrdp	/var/log/xrdp.log	Speaks the RDP protocol. Interfaces to an X server (Xorg or Xvnc) which is run as part of the session startup
xrdp-sesman	/var/log/xrdp-sesman.log	Responsible for authenticating the user, and starting the session
PAM modules	TODO	TODO
Xorg	TODO	TODO
Window manager	TODO	TODO

This is simplifying slightly, when xrdp asks xrdp-sesman to authenticate a user and start a session, it receives a single value back. This value is the display number of the started X server, with 0 being used to report failure. login failed for display 0 therefore means some kind of authentication failure, or a failure of the early stages of session initialisation.

Troubleshooting

Here is a non-exhaustive list of possible reasons for login failure:

• The password for the user is incorrect
• The PAM stack has failed to authenticate (or authorize) the user for some reason.
• xrdp-sesman is unable to find a spare display number.
• failure of the early stages of Xorg session initialisation.

The first place to start is to look in the log file for xrdp-sesman where more information will be available.