This is on a Debian box. RedHat might be a bit different, but this should get you the idea. # ls -l /dev/ttyS0 crw-rw---- 1 root dialout 4, 64 May 1 16:26 /dev/ttyS0 So root and users in the dialout group can read and write to the serial port. So check your user: groups zibby zibby : zibby src music Hmmm, zibby isn't in dialout. # sudo adduser zibby dialout Password: Adding user zibby to group dialout... Done. # groups zibby zibby : zibby dialout src music There we go. Now all zibby (me!) needs to do is logout and login again to refresh group permissions to access the serial port. Andrew S. Zbikowski | http://www.ringworld.org "The irony is that Bill Gates claims to be making a stable operating system and Linus Torvalds claims to be trying to take over the world."