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[solved] Multiple thin client support
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Joined: 05 Oct 2005
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Location: DC Burbs

PostPosted: Wed May 11, 2016 4:08 am    Post subject: [solved] Multiple thin client support Reply with quote

It's funny how that which was old has come around to being new again. I'm in the process of setting up servers which will support a network consisting of mainly HP thin clients. So I'm back to that time honored tradition of using xdmcp to remote session in. Don't suggest anything more secure or like vnc since these thin client loadsets are based on a version of debian squeezed into a 1 or 2gb ssd drive via squashfs. They can basically do rdp or xdmcp session and not much else and don't have local logins or membership in our Active Directory domain.

While wishing I could use gentoo on the server, I'm actually stuck with rhel6.5. That pretty much limits me to either gdm or kdm for display manager. However it might be interesting to try this exercise with lightdm or sddm at some point and our favorite distro.

I have a few rhel5 servers set up in this space, and they immediately showed up and offered a desktop login when I did a chooser or broadcast style session. However the gnome version (2.30?) and gdm for rhel6 is turning out to be a real PITA.

When I first played around with the /etc/gdm/custom.conf and /etc/X11/xdm/Xaccess files to get this working, I was on my gentoo based ceph cluster at home with an rhel6.5 reference vm and a win10 based laptop running a recent version of cygwin with a working cygwin-x setup. I did actually manage to get gdm on rhel6 to give me a login session and then got into a desktop. With firewalls disabled on both sides this custom.conf works:

# GDM configuration storage



DisplaysPerHost = 4




The crucial one line I always forget about in /etc/X11/xdm/Xaccess needs to be uncommented out:

*               #any host can get a login window

That config let me do the following from a cygwin bash shell on the pc:

x -query 192.168.blah.blah

where the ip address is what my dhcp server assigned my reference vm when it fired up in libvirt/kvm. I assumed I would be able to setup an HP thin client to do an xdmcp with -query and the hostname at work after dropping similar conf files down on its rhel6.5 install and did the telinit 3, telinit 5 tap dance.

The result was the infamous black screen xdmcp session which I eventually put out of its misery. The /var/log/gdm/gdm-binary log file mumbled something about temporary name resolution failures every few seconds but nothing other than that. Enabled debug in the custom.conf and did the telinit dance again. This time the gdm-binary log mumbles additional things about null host and domain names. Running wireshark and watching all traffic based on the thin clients ipv4 address at the host shows that a single xdmcp packet gets logged with only ip addresses in the headers and not much else in the meat of the packet. So it would appear that the rhel6 gdm does not like the offerings served up by lowly debian based thin clients.

I had done a full boat install of rhel6.5 on this server, including the full kde desktop with kdm. So I proceeded to toss gdm by the wayside and enabled kdm to provide the display management. This worked the first time like a champ. I dread the day when I have to do this exercise again with rhel7, since they conveniently left out kdm from any of the kde packaging (but they are still stuck back in middle version 4.x!)

I need to go back and see what I need to do with /usr/share/config/kdm/kdmrc to handle more than one or two remote sessions. The maxsession, etc syntax from the gdm custom.conf is not appropriate or I'm just missing its proper placement in forest of sections with comments in that file. Can anybody chime in with something they may have already done along a similar vein? Also is anybody doing anything like this with other display managers?

Last edited by vaxbrat on Mon May 16, 2016 5:32 am; edited 1 time in total
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Joined: 05 Oct 2005
Posts: 731
Location: DC Burbs

PostPosted: Mon May 16, 2016 5:31 am    Post subject: Tweaking remote counts Reply with quote

Looks like the only thing I needed to tweak is the count of ReserveServers in /usr/share/config/kdm/kdmrc. Displays 1-3 are set up by default:

# This option exists solely for the purpose of a clean automatic upgrade.
# Do not even think about changing it!
# List of permanent displays. Displays with a hostname are foreign. A display
# class may be specified separated by an underscore.
# Default is ":0"
# List of on-demand displays. See StaticServers for syntax.
# Default is ""

so just add more. In my case I told it to set aside a dozen:

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