Thin Client replacement

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Hello,

we're looking to replace the expensive, virus-ridden, wall mounted "Thin
Client" Windows computers with something cheap and safe. The tasks are:

- IP address over DHCP
- some terminal windows (to telnet into an ancient mainframe)
- web browser
- no network connections accepted from the outside

After power up and afterwards, the predefined applications must come up
automatically. No login should be neccessary, and no user action should be
required to open or move any windows around. Web browser and terminal
windows should restart and connect to predefined addresses if closed by
accident.

As this device will be running 24/7 in an industrial production environment,
worst-case maintenance must be a single power cycle to bring a crashed
system up again.

I'm familiar with running a Debian/dwm desktop system.

Any suggestions on how to go about this?
**Daniel

robert

Re: Thin Client replacement
Robert Latest wrote:

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Rasberry Pi or Beagle Bone Black should be able to do all you need.  You can  
restrict things as much as you want in Linux.  OK, power cycling crashed  
Linux systems is not the best for file system integrity.  On the other hand,  
if you get rid of all unneccesary tasks, they ought to run for many months  
at a time.

Jon

Re: Thin Client replacement
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we run around 12 PIs since more than 2 years 24/365. First with a normal
image, since last year with a ro rasbian. Have a copy of the sd card and a
problem with the card / FS is no problem. Before we use EEEPCs for this task.

The PIs are cups servers for printers and do a ssh with ssh_keys and get a
terminal programm for some information and for managing the print queues.

They are no thin clients.

Juergen

Re: Thin Client replacement
On 18/05/17 16:01, Robert Latest wrote:
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Tick, trivial
Tick, trivial

Tick, trivial

Tick, but a little more of a firewall setup challenge

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Tick, trivial

No login should be neccessary,
Tick, trivial

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? Not sure what you expect to move the windows if the user doesn't.

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Mmm. possible but less simple. A watchdog script in a timer?

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Mm. Some judicious use of read-only file systems may be indicated.
OR you might run it all in  a virtual machine so that 'restore from  
snapshot' is an option

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Id personally go with Mint and probably Mate or XFCE as a staring point,  
after deciding what partitions to create and whether or note read only  
is the way to mount them

Then start to build up eh parts bit by bit.

I would imagine a startup script could be inserted into teh init.d  
system to, after the window manager stars up launch what apps in what  
window arrangements are desirable

It been a long time, but I think you can set command line options  
somehow top preconfigure where and what size the windows ill be.

It may be, and I am way over my pay grade here, that you dont need a  
window manager at all, but could just launch the apps into X-space.
That way there is no window manager to resolve etc etc.

Watchdog uses `ps` to ID what apps are running and restart them if they  
crash



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Re: Thin Client replacement
On Thu, 18 May 2017 20:55:26 +0100, The Natural Philosopher wrote:

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..but easy to check: run nmap from any other host that can see the screen  
with the -pn option. When it sees nothing then you've got all ports  
blocked from accepting outside connection requests.
  
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... ish. Would be more reliable with the filing system on a hard drive or  
an SSD than an SD card because both are somewhat harder to corrupt by  
pulling the plug than an SD card is. Search previous history on this  
newsgroup for threads about that. If you have a suitable 24x7 server you  
can connect to and keep data on, that may be the best place to put the  
flatscreen's filing system. You can use nfs or some other remote FS, e.g.  
Samba, to mount it once the flatscreen device has booted off a local read-
only filing system.

  
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Indeed, though if you want to put more than one full-screen window on the  
display that could be problematic no matter what OS and applications you  
run. Bit see my last point for more detail

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Agreed, but it may combine with my next point.

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Yep.
  
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Yes, that would work, and you could use frequently executed cron jobs to  
detect that some application has fallen over and restart it, emailing yo  
an alarm if it fails more than 'n' times in a row.

If you use a systemd based system, e.g. current Raspbian versions on a  
RaspberryPi, then you can use a set of systemd services to (a) start  
everything yo need at boot time and (b) to restart anything that fails

That may be simpler that using an rc.init script plus a set of cron  
scripts, particularly as the old SystemVinit system is only present in  
systemd installations to allow daemons that haven't yet been ported to  
systemd to be run.

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That will depend on the individual application and, to a lesser extent,  
on whatever window manager you're using.
  

--  
martin@   | Martin Gregorie
gregorie. | Essex, UK
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Re: Thin Client replacement
On 18/05/17 22:31, Martin Gregorie wrote:
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My thought actually is, does one need a window manager at all?



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Re: Thin Client replacement
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I'm assuming the OP wants a fixed layout, eg browser window full height on
the left, then two terminal windows stacked on the right.

Something like that is doable without a window manager, but the problem then
becomes how to switch focus from one window to another.  I don't think you
can do that without a window manager.

It's probably a case of carefully selecting a window manager that allows
launching of apps to particular sizes, and pinning of windows so they won't
move.  Or one that has a 'tile windows' function that tiles them into
approximately the right layout.

Theo

Re: Thin Client replacement
On 2017-05-19, Theo wrote:
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A tiling WM (such as dwm) would probably be the best bet; or you could
disable moving/resizing on a normal WM, and perhaps use wmctrl to put
the windows in specific places.

Re: Thin Client replacement
On 19/05/17 10:17, Theo wrote:
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Ratpoison?
(Kills all mice)

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Ah, you have confirmed that I was somewhat above my pay level...yes.  
Keyboard focus and the like...



--  
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conventions is invited to try transgressing those conventions from the  
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Re: Thin Client replacement
On 18/05/17 22:31, Martin Gregorie wrote:
....
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Am I missing something here? What's wrong with each task being wrapped  
in a trivial shell script that loops forever, eg:

while true; do xterm -e ssh myhost;  mail root -s 'ssh exited'  
</dev/null; done

or similar.

--  
Mike Scott (unet2 <at> [deletethis] scottsonline.org.uk)
Harlow Essex
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Re: Thin Client replacement
On 19/05/17 09:28, Mike Scott wrote:
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Hmm. You are assuming it crashes in a way that will exit back to that?

When we did watchdogs in milspec stuff it tended to be within the app,  
write a number that increments every time you write it, outside the app  
(under timer interrupt) if the number doesnt get updated for n seconds,  
destroy the process and recreate it. (or in many cases reboot the whole  
embedded system)

That takes care of 'hung' processes as well



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Re: Thin Client replacement
On 19/05/17 09:32, The Natural Philosopher wrote:
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No, just fulfilling the OP's stated requirement: "Web browser and  
terminal windows should restart and connect to predefined addresses if  
closed by accident."

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Horses for courses. I don't think the OP is concerned to that level. IMBW.
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--  
Mike Scott (unet2 <at> [deletethis] scottsonline.org.uk)
Harlow Essex
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Re: Thin Client replacement
On 22/05/17 08:36, Mike Scott wrote:
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You don't think that crashing is a member of the set of 'closed by  
accident' then?



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Re: Thin Client replacement
On Fri, 19 May 2017 09:32:52 +0100

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    If the xterm or ssh in that example crash then the shell loop will
certainly continue. If the shell crashes (very rare indeed), or the
processes hang then it won't.

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Re: Thin Client replacement
Ahem A Rivet's Shot wrote:

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Write a systemd service unit for it, with a restart=always clause

v
v
v
v
v
v
v
v
v


then when PID 1 crashes .... D&RFC

Re: Thin Client replacement
On Fri, 19 May 2017 09:28:34 +0100, Mike Scott wrote:

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That looks a bit aggressive: shouldn't it check that the process has in  
fact crashed before restarting it?  




--  
martin@   | Martin Gregorie
gregorie. | Essex, UK
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Re: Thin Client replacement
On 05/18/17 14:31, Martin Gregorie wrote:
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systemd isn't present on FreeBSD, and FBSD 11 has some excellent RPi  
support.

If you want a truly headless system, you can run tightvnc server to  
allow clients to VNC into the device for a web browser or GUI and no  
need for a login either (except for the VNC session password itself,  
which would be smart to have)

Also Raspbian prior to 'Jessie' had systemV, not systemd, so you're  
golden.  I don't use Raspbian with systemd in it.  I keep the old image  
around and it's just fine.  And USB bluetooth works properly [still  
broken in Jessie last I checked].


Re: Thin Client replacement
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It's not clear to me if you are still wanting the Pi to be a
thin client or not.

There are several pre-canned raspberry pi thin client solutions,
some free, some charge a license fee.

One key issue is if you expect to play video. If so, you will
need a solution like citrix which traps the mpeg stream at the
server, and pipes that across for decoding in the hardware codecs
on the Pi.  If you can make do without video, then you have lots
more options.

If you want to run directly on the Pi, terminal windows are no
problem. Modern web browser is too big to run with any performance.
Some of the cut-down browsers will perform better, but will not
provide a modern experience, will not handle some web sites
properly, and will feel old.

--  
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Re: Thin Client replacement
Andrew Gabriel wrote:
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Frankly, I don't even know what "thin client" really means -- all I know is
that the current Windows-based wall-mounted PCs are called thin clients,
and this colleague of mine and I want to replace them with cheap, reliable
stuff.

This is big corporation type issue. Windows OS and hardware is leased from
and maintaned by an external contractor, with extra charges for units
deployed on the 24/7 shop floor. Huge cost for a few hundred terminals and
web browsers.

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"Browser experience" is not an issue. The browser is only needed for
quasi-static, text-only, purely technical content in an industrial
production environment. An ncurses-based text-only browser is out due to
lack of user acceptance and smooth transition from today's GUI (IE)
solution.

robert

Re: Thin Client replacement
On 26/05/17 06:54, Robert Latest wrote:
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Originally a 'thin client' was a serial terminal. Where all the clever  
stuff is dine on the server.

Whether a browser is a thin or a thick client depends on how much  
JavaScript you write :-)

Arguably a browser interfacing to a database is pretty 'thin' - its just  
a terminal with some graphics ability.


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Yep.

Yep. Plenty of options for a basic browser. Especially if you can  
restrict web pages to exactly what it understands and format exactly for  
the screens available. Heck you could go back to firefox release 3 or  
something...

You could, given the simplicity of what you appear to want, even write  
your own cut-down browser in python or something.

One of the advantages of a private industrial installation is that you  
ought to be able to come up with a configuration that needs no upgrades  
ever.

Until the hardware is so obsolete it cant be replaced or fixed.



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