Using GDM and XDMCP with remote client

How to run Xorg session on client machine.

On the server (IP 10.10.10.1) by default GDM remote connect via XDMCP is disabled. We need to enable it. Configuration file is /etc/gdm/custom.conf (on RHEL/Oracle Linux) and /etc/gdm3/daemon.conf (on Debian). Example is from Oracle Linux 6.4:

# cat /etc/gdm/custom.conf
# GDM configuration storage

[daemon]

[security]

[xdmcp]

[greeter]

[chooser]

[debug]

Add these lines:

# cat /etc/gdm/custom.conf
# GDM configuration storage

[daemon]

[security]
DisallowTCP=false

[xdmcp]
Enable=true

[greeter]

[chooser]

[debug]

GDM must be restarted for this to work.

On client machine start the Xorg server like this (assuming that you have already X running on :0):

# X :1 -query 10.10.10.1

This will bring GDM to your display at display :1 and now you can login and work on client machine as you are logged directly to the server and switch between local and remote X with Alt + Fxx.

Roundcube missing contacts after changing IP address of the server.

If you have working installation of Roundcube and for some reason change your IP address the result is missing address book entries of all users.

If in the configuration file config/main.inc.php the line:
$rcmail_config['default_host'] = '10.10.200.1';
is changed to some other IP address (for instance 192.168.10.1) the result is missing address book entries.

In fact entries are not missing but Rouncube shows only enties for the users with current 'default_host' IP address. This means that you have two entries for each users with different 'default_host' field. How to fix it?

First delete all newly created entries with the new default_host:
old: 10.10.200.1, new: 192.168.10.1.

# mysql -u roundcubeuser -proundcubepass
mysql> use roundcube
mysql> delete from users where mail_host='192.168.10.1';
Query OK, 60 rows affected (0.07 sec)

Now change all remained entries with the new default_host:

mysql> update users set mail_host='192.168.10.1' where mail_host='10.10.200.1';
Query OK, 105 rows affected (0.08 sec)
Rows matched: 105  Changed: 105  Warnings: 0

Now you have your addressbook back.