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7. Serial Port Devices /dev/ttyS2, etc.

For creating devices in the device directory see

Creating Devices In the /dev directory

7.1 Serial Port Device Names & Numbers

Devices in Linux have major and minor numbers. Each serial port may have 2 possible names in the /dev directory: ttyS and cua. Their drivers behave slightly differently. The cua device is deprecated and will not be used in the future. See the Modem-HOWTO section: "The cua Device".

Dos/Windows use the COM name while the setserial program uses tty00, tty01, etc. Don't confuse these with dev/tty0, dev/tty1, etc. which are used for the console (your PC monitor) but are not serial ports. The dos names (COM1, etc.) and IO address is shown below for the "standard" case (but yours could be different).

       set-                                              IO
dos   serial          major minor         major minor  address
COM1  tty00  /dev/ttyS0  4,  64;  /dev/cua0  5,  64      3F8
COM2  tty01  /dev/ttyS1  4,  65;  /dev/cua1  5,  65      2F8
COM3  tty02  /dev/ttyS2  4,  66;  /dev/cua2  5,  66      3E8
COM4  tty03  /dev/ttyS3  4,  67;  /dev/cua3  5,  67      2E8
Note that all distributions should come with ttyS devices (and cua devices until cua is finally abolished). You can verify this by typing:

linux% ls -l /dev/cua*
linux% ls -l /dev/ttyS*

7.2 Link ttySN to /dev/modem ?

On some installations, two extra devices will be created, /dev/modem for your modem and /dev/mouse for your mouse. Both of these are symbolic links to the appropriate device in /dev which you specified during the installation (unless you have a bus mouse, then /dev/mouse will point to the bus mouse device).

There has been some discussion on the merits of /dev/mouse and /dev/modem. The use of these links is discouraged. In particular, if you are planning on using your modem for dialin you may run into problems because the lock files may not work correctly if you use /dev/modem. Use them if you like, but be sure they point to the right device. However, if you change or remove this link, some applications might need reconfiguration.

7.3 Notes For Multiport Boards

For board addresses, and IRQs, look at the rc.serial or /etc/rc.boot/0setserial that comes with the setserial program. It has a lot of detail on multiport boards, including I/O addresses and device names.

7.4 Creating Devices In the /dev directory

If you don't have a device, you will have to create it with the mknod command. Example, suppose you needed to create devices for ttyS0:

linux# mknod -m 666 /dev/cua0 c 5 64
linux# mknod -m 666 /dev/ttyS0 c 4 64
You can use the MAKEDEV script, which lives in /dev. See the man page for it. This simplifies the making of devices. For example, if you needed to make the devices for ttyS0 you would type:
linux# cd /dev
linux# ./MAKEDEV ttyS0
This handles the devices creation and should set the correct permissions.


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