I wrote a little test program in c++ to read data from ttys0. It works but only as root! I have set the user to be a member of tty, I have even tried to set the ttys0 device to 777. Nothing but running as root seems to work. Any suggestions?

I take it /dev/ttyS0 is in the tty group? Because on my system:

crwxrwxrwx 1 root tty 3, 48 2004-12-03 13:50 /dev/ttys0

As you can see I have even gone so far as to make it world rwx Not the best plan for security I know but the box is not on a network yet.

Please show us the code you're using to access it.

Here is the source to the object I wrote to read the serial port.
I am using Linux

//
// File: kybdevice.cc
// Created on: Mon Apr 11 15:01:33 2005
//

#include "kybdevice.h"


kybdevice::kybdevice()
{ // init
errorcode=0;
// Open serial port
fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY );
if (fd <0) {perror(MODEMDEVICE);
errorcode=44;
}else{
tcgetattr(fd,&oldtio); /* save current port settings */
memset(&newtio, 0, sizeof(newtio));
newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;
newtio.c_iflag = IGNPAR;
newtio.c_oflag = 0;
/* set input mode (non-canonical, no echo,...) */
newtio.c_lflag = 0;
newtio.c_cc[VTIME] = 1; /* inter-character timer unused */
newtio.c_cc[VMIN] = 1; /* blocking read until 5 chars received */
tcflush(fd, TCIFLUSH);
tcsetattr(fd,TCSANOW,&newtio);
}

}


kybdevice::~kybdevice()
{
// TODO: put destructor code here
if(!errorcode){
tcsetattr(fd,TCSANOW,&oldtio);
}
}

int kybdevice::getKeystrokes(unsigned char *buffer, int bufsze){
res = read(fd,buffer,bufsze);
buffer[res]=0;
}
int kybdevice::getError(void){
return errorcode;
}
return 28;
}

Where it stops when you run it as non-root. At open() call?