[RESOLVED] External program output redirection

Marinese

Hi!
I have a LED-sign which i want to control through php, but i can't get it to work from online-based php. The sign is controlled through a program which output is redirected to the sign, for example

./sign "hello world" > /dev/ttyUSB0

If i make a php script which contains

$foo="/blabla/sign \"hello world\" > /dev/ttyUSB0";
echo exec($foo);

It executes fine and the sign displays the text if I execute it from commandline, i e php myscript.php, but it does not work when accessed from the internet. No error is given, and it displays ok on the screen if I remove the output redirection, so there has to be som problem with output redirection with this code and online execution. Anybody has any ideas?

bradgrafelman

The webserver that hosts the site is on the same computer that you tested the script via the command line, right?

Assuming the answer is yes, my guess is that the user that Apache is running under (e.g. "www", "httpd", "apache", etc.) doesn't have permissions to write to the hardware device (whereas you do - and PHP is using your permissions since you invoked the parser rather than the webserver daemon).

jkurrle

So couldn't the script execute an "SU" command (assuming linux) to attain sufficient permissions to run the sign? Granted, it could easily be a security violation, but if one were to carefully tailor a user account's permissions, I could see it function within an acceptable security profile...

Marinese

Thanks for the help! Changed permission on /dev/ttyUSB0 to 666 and now everything works.