[R] X11 connection error in web cgi mode only

Pikounis, Bill v_bill_pikounis at merck.com
Mon Mar 17 16:33:43 CET 2003

I think this issue or something very related to it has come up before in
this list, so you may wish to search the R-help mail archives.   From what
you say, my guess on the reason for the error is permissions related, as the
web server (Apache?) executing your CGI does not implictly have access to an
X resource, which jpeg needs to work.

I have had some luck using "Xvfb" under Linux for CGI scripts with R to
generate PNG format data graphs. But this is a work-in-progress, as I have
not solved the permissions problem with a secure method yet.  Plus there is
the complication of cleanly accessing an X display in a multi-user system.  

You can learn much about Xvfb via google.

Hope that helps,
Bill Pikounis, Ph.D.

Biometrics Research Department
Merck Research Laboratories
PO Box 2000, MailDrop RY84-16  
126 E. Lincoln Avenue
Rahway, New Jersey 07065-0900

v_bill_pikounis at merck.com

Phone: 732 594 3913
Fax: 732 594 1565

> -----Original Message-----
> From: Adaikalavan Ramasamy [mailto:gisar at nus.edu.sg]
> Sent: Monday, March 17, 2003 8:43 AM
> To: r-help at stat.math.ethz.ch
> Subject: [R] X11 connection error in web cgi mode only
> Dear all,
> I am trying to create a web interface using Perl-CGI to call 
> R plots and
> to display them.
> The following codes works perfectly fine when I copy and 
> paste into the
> console directly or if I save it into script.file and then R 
> --no-save <
> script.file producing the graphs. 
> jpeg("graph.jpeg", width=400, height=400)
> plot(rnorm(100))
> dev.off()
> Now, I put the line system("R --no-save < script.file > 
> log_file") from
> inside my cgi and then process it from client side, I get the 
> following
> error message:
> Error in X11(paste("jpeg::", quality, ":", filename, sep = ""), width,
> : 
>         unable to start device JPEG
> In addition: Warning message: 
> unable to open connection to X11 display`' 
> Execution halted
> Why do I get this error and how can I fix it? Many thanks in advance.
> Regards, Adai.
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help


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