It's most likely modem-manager. `sudo lsof | grep ttyS0` should tell you for sure.
-- efax- Warning: /dev/ttyS0 locked or busy - waiting https://bugs.launchpad.net/bugs/491275 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
