Re: 20040803: "DISPLAY" problem in GEMPAK script

John,

To run a script from cron, you need to be able to connect to
an X server, or a virtual X server (eg Xvfb).

When you said you ran from a script, I assumed you were running the
script at your console and not from a cron.

There is no DISPLAY variable in a cron until you set one.
When you log in to a consolu running X, you are running an X_init or
startxwin type of script that sets up an environment for you.

To use an Xvfb to generate displays, you can create a 24 bit depth
server with:
Xvfb :1 -screen 0 1280x1024x24 &
I do that in an init.d level script at startup rather than in a user
script.

You can use an /etc/X1.hosts file to enable connection from 
a list of allowed hosts (the "1" in X1.hosts is for display :1 
as invoked above).

After running the Xvfb command above, you will be able to display to
your `hostname`:1.0

Steve Chiswell
Unidata User Support





On Tue, 2004-08-03 at 15:14, unidata wrote:
> Hi --
> 
> 
> Thanks for the quick response.
> 
> > > Check to see what your DISPLAY variable is when you are running the
> > > program interactively. Your default display now may not be the same
> > > as what you are setting in your script.
> 
> I had done that before -- typed env and look what display had been set at, 
> and set the script to that value  -- with no luck.   However, I also started 
> to do a grep search on my old emails and was surprised to see a recent 
> message on a similar problem (         Re: Crontab creating Gempak *.gif 
> images   26 July)  and tried the solution.  Indeed,  I had no Xvfb running.  
> I used Mike Voss's template and got different problems.  Using the script 
> file, gempak accepted the DISPLAY, (or perhaps choked before it got to that 
> part), but then gave an error on not having read/write colors (I am not sure 
> the exact error message, but an error type that started with N  and could 
> have been NCLR). 
> 
> I then got your email,determined the value for DISPLAY that was the 
> environment for the session, set the script to that (with the Xvfb running) 
> and the script ran fine.   I then went back and changed the script used in 
> the web page -- the one that alerted us to the problem -- and changed it to 
> that value, :0.0 , and got this response.
> Xlib: connection to ":0.0" refused by server
> Xlib: No protocol specified
> [GEMPLT -83]  NDISP - DISPLAY not set or invalid
> 
> I then took out the   setenv DISPLAY  line in the web script, and added a 
> line that dumped  the results of   env  to the web page, and discovered there 
> was no native DISPLAY value in the web's http account and got a gempak 
> response of
>  [GEMPLT -83] NDISP - DISPLAY not set or invalid Parameters requested:
> 
> As I read it,  at this stage,  
> 1)  the web page script needs a  setenv DISPLAY command line to work under 
> the web account.  There is no global value for DISPLAY.
> 
> 2)  Xvfb needs to be running, though I am not sure the template Mike Voss 
> used is the right one for my system.   I don't know if it needs to be 
> established for each account ,  or that it can work with one instance 
> running, started at boot time.
> 
> Any ideas?
> 
> Thanks again,
> 
> Hobbie