Dave Cooper dave@accuramatic.co.uk wrote:
As su, chmod 777 /dev/ttyS0 fixes it, but only until it happens again. ttyS0 appears to be owned by root. It seems to me maybe it should be owned something/someone else to fix this permissions problem but I don't have a clue who. Can anyone put me right on this please?
Look at what group ttyS0 belongs to. Try ls -l /dev/ttyS0 The group name will probably be just after the "root". Then, add your user(s) to that group with the command usermod -a -G whatevergroupnameitsaid username or if that doesn't work, edit /etc/group to add the username to the end of the line starting with whatevergroupnameitsaid.
Alternatively, change the permissions on /dev/ttyS0 forever. These days, that's often done by udev, so grep -r /etc/udev/rules ttyS to try to find where the MODE is set.
Hope one of those works for you,