Why can't my scripts execute external programs with GUI frontends from within Apache/mod_perl when I could under Win9.x?
The issue is not an Apache/mod_perl issue per se. Any service that allows execution of external binaries that try to initialize and display GUI components will have problems under OSs like Windows 2K+, Unix, Linux and MacOS X.
This would have worked in Win 98 because apps all run in the same user space (under the same user ID). Those resources happened to be, for the most part, linked to almost everything else running on the system. Hence when you ran a gui app from within Apache the system would display the gui part of it on the screen. The OS saw no difference between the web server running in the background and the user's desktop.
The best way to deal with this is to see if the application you are trying to run has a /quiet switch or something that will keep it from trying to draw any GUI components/dialog boxes to the screen. If you wrote the application you are trying to execute then you should put a hook into it that will allow that option (obviously adding the code to bypass the gui code) and then execute it with the new option. The best way to execute programs under Perl's system call is to write a console application. If you would like to take output from that application then you should write to STDOUT all text you want the perl application to see as a return value from your system() call or `` (backticks) call.
Tom
Stas Bekman wrote:
Terra Info wrote:
I will write up a more publically palatable version of the below and post it for someone more intimately associated with the docs and development to merge into the tree.
Great, thank you!
Keep in mind that this is an issue not just for MP but also any CGI script or frankly any service that allows execution of external binaries that try to initialize and display GUI components. Although I have not tested it, I would imagine that this would be an issue on a Unix/linix variant as well as the design of the OS is similar to WinNT and up. Or the other way around if you want to follow the timeline correctly ;-}.
I believe that Unix users are aware of this issue from the very first steps of using the system and therefore we hardly ever see this kind of questions on this list. Apparently permissions on winNT is something unexpected and new for those who are used to older win32 systems. Moreover, error_log usually tells what the exact problem is when the code is written properly to report errors (e.g., checking the return status of system()). My guess is that this should work on winNT too.
If there are similar issues with MacOS X or other platforms, please send the info in, so we will add it to the docs. Though my guess is that MacOS X is based on FreeBSD and therefore all the normal Unix perms concepts apply as is. Correct me if I'm wrong.
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