I'm trying to access the parallel port (/dev/lp0) from a non root process.
Basically I have a program that can only access the port if it runs as root.
Here's what happens when I run as root:
root@falcon:~/src/k74-1.0# ./pprxtx all set
root@falcon:~/src/k74-1.0# ./pprxtx read
255
root@falcon:~/src/k74-1.0# ./pprxtx all clear
root@falcon:~/src/k74-1.0# ./pprxtx read
0
Here's what happens when I run as a non root user (ed):
ed@falcon:~/src/k74-1.0$ ./pprxtx all set
/dev/port: Permission denied
ed@falcon:~/src/k74-1.0$ ./pprxtx read
/dev/port: Permission denied
/dev/lp0 I thought that all I had to do was to add my non rootport user to
the device group (lp) in /etc/group and then that user would have
permissions to read and write to that device.
lp:x:7:cupsys, ed
I also changed the device permissions to
/dev:
crw-rw-rw- 1 root lp 6, 0 2006-09-21 04:56 lp0
I still can't access the port unless I run as root.
If I change the /dev/port (dangerously insecure) permissions to
/dev:
crw-rw-rw- 1 root kmem 1, 4 2006-09-21 04:56 port
I then get:
ed@falcon:~/src/k74-1.0$ ./pprxtx read
/dev/port: Operation not permitted
ed@falcon:~/src/k74-1.0$ ./pprxtx all set
/dev/port: Operation not permitted
Any ideas? I've done a fair amount of googling this and it seems like I'm
doing everything correctly.
Thanks,
--
Ed