pySerial- need help.

[Joal Heagney]

kamarudin samsudin wrote:
> Hi all,
> 
> I try to invoke python serial script via my browser using PHP (exec
> function). For the serial communication, i used pySerial module. It
> fine when it run it as root but when i try to run it from browser, i
> got this error in my httpd/error_log
> 
>   File "weather1.py", line 9, in ?
>     ser=serial.Serial('/dev/ttyS0',9600,timeout=1)
>   File "/usr/lib/python2.3/site-packages/serial/serialutil.py", line
> 153, in __init__
>     self.open()
>   File "/usr/lib/python2.3/site-packages/serial/serialposix.py", line
> 137, in open
>     raise SerialException("Could not open port: %s" % msg)
> serial.serialutil.SerialException: Could not open port: [Errno 13]
> Permission denied: '/dev/ttyS0'
> 
> i tried chmod go+wr /dev/ttyS0 but i still got the error.
> 
> BTW, i used apache 2.0.52, PHP 4.3.10 and Fedora Core 3 
> 
> Thanks in advance.
> 
This sounds more like a linux problem rather than a python problem. 
Modern linux'es set the permissions in /etc/security files, and these 
will override any chmod that you do in the /dev/ directory. What you 
need to do is edit /etc/security/console.perms file.

In Mandrake I have the following lines:

------------------------------------------------
<serial>=/dev/ttyS* /dev/rfcomm* /dev/ircomm*
---and lower down ---
<console>  0660 <serial>     0660 root.uucp
------------------------------------------------
You can change the <console> / <serial> line so that you have 666 
permissions, but it would probably be better to ensure that the serial 
is assigned a non-root group (uucp in my case), change the group of your 
script to match, set the sgid bit on your program and change the execute 
permissions on your script so everyone can use it.

chmod 2755 <script>

This way your script will execute as group uucp, and theoretically it 
should have permission to access the /dev/ttyS* devices.

Hope that helps,

Joal