Most devices in the kernel are accessed through ``device special
files'', which are located in the /dev directory. The
sio devices are accessed through the /dev/ttyd?
(dial-in) and /dev/cua0? (call-out) devices. On FreeBSD
version 1.1.5 and higher, there are also initialization devices
(/dev/ttyid? and /dev/cuai0?) and locking devices
(/dev/ttyld? and /dev/cual0?). The initialization
devices are used to initialize communications port parameters each
time a port is opened, such as crtscts for modems which use
CTS/RTS signaling for flow control. The locking devices are
used to lock flags on ports to prevent users or programs changing
certain parameters; see the manual pages termios(4), sio(4),
and stty(1) for information on the terminal settings, locking
& initializing devices, and setting terminal options,
respectively.
A shell script called MAKEDEV in the /dev directory
manages the device special files. (The manual page for
MAKEDEV(8) on FreeBSD 1.1.5 is fairly bogus in its discussion of
COM ports, so ignore it.) To use MAKEDEV to make dialup
device special files for COM1: (port 0), cd to /dev
and issue the command MAKEDEV ttyd0. Likewise, to make dialup
device special files for COM2: (port 1), use MAKEDEV ttyd1.
MAKEDEV not only creates the /dev/ttyd? device special
files, but also creates the /dev/cua0? (and all of the
initializing and locking special files under FreeBSD 1.1.5 and up) and
removes the hardwired terminal special file /dev/tty0?, if it
exists.
After making new device special files, be sure to check the
permissions on the files (especially the /dev/cua* files) to
make sure that only users who should have access to those device
special files can read & write on them - you probably do not want
to allow your average user to use your modems to dialout. The default
permissions on the /dev/cua* files should be sufficient:
crw-rw---- 1 uucp dialer 28, 129 Feb 15 14:38 /dev/cua01
crw-rw---- 1 uucp dialer 28, 161 Feb 15 14:38 /dev/cuai01
crw-rw---- 1 uucp dialer 28, 193 Feb 15 14:38 /dev/cual01
These permissions allow the user uucp and users in the group
dialer to use the call-out devices.