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| -rw-r--r-- | Documentation/admin-guide/serial-console.rst | 115 |
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diff --git a/Documentation/admin-guide/serial-console.rst b/Documentation/admin-guide/serial-console.rst new file mode 100644 index 000000000..a8d1e36b6 --- /dev/null +++ b/Documentation/admin-guide/serial-console.rst @@ -0,0 +1,115 @@ +.. _serial_console: + +Linux Serial Console +==================== + +To use a serial port as console you need to compile the support into your +kernel - by default it is not compiled in. For PC style serial ports +it's the config option next to menu option: + +:menuselection:`Character devices --> Serial drivers --> 8250/16550 and compatible serial support --> Console on 8250/16550 and compatible serial port` + +You must compile serial support into the kernel and not as a module. + +It is possible to specify multiple devices for console output. You can +define a new kernel command line option to select which device(s) to +use for console output. + +The format of this option is:: + + console=device,options + + device: tty0 for the foreground virtual console + ttyX for any other virtual console + ttySx for a serial port + lp0 for the first parallel port + ttyUSB0 for the first USB serial device + + options: depend on the driver. For the serial port this + defines the baudrate/parity/bits/flow control of + the port, in the format BBBBPNF, where BBBB is the + speed, P is parity (n/o/e), N is number of bits, + and F is flow control ('r' for RTS). Default is + 9600n8. The maximum baudrate is 115200. + +You can specify multiple console= options on the kernel command line. +Output will appear on all of them. The last device will be used when +you open ``/dev/console``. So, for example:: + + console=ttyS1,9600 console=tty0 + +defines that opening ``/dev/console`` will get you the current foreground +virtual console, and kernel messages will appear on both the VGA +console and the 2nd serial port (ttyS1 or COM2) at 9600 baud. + +Note that you can only define one console per device type (serial, video). + +If no console device is specified, the first device found capable of +acting as a system console will be used. At this time, the system +first looks for a VGA card and then for a serial port. So if you don't +have a VGA card in your system the first serial port will automatically +become the console. + +You will need to create a new device to use ``/dev/console``. The official +``/dev/console`` is now character device 5,1. + +(You can also use a network device as a console. See +``Documentation/networking/netconsole.txt`` for information on that.) + +Here's an example that will use ``/dev/ttyS1`` (COM2) as the console. +Replace the sample values as needed. + +1. Create ``/dev/console`` (real console) and ``/dev/tty0`` (master virtual + console):: + + cd /dev + rm -f console tty0 + mknod -m 622 console c 5 1 + mknod -m 622 tty0 c 4 0 + +2. LILO can also take input from a serial device. This is a very + useful option. To tell LILO to use the serial port: + In lilo.conf (global section):: + + serial = 1,9600n8 (ttyS1, 9600 bd, no parity, 8 bits) + +3. Adjust to kernel flags for the new kernel, + again in lilo.conf (kernel section):: + + append = "console=ttyS1,9600" + +4. Make sure a getty runs on the serial port so that you can login to + it once the system is done booting. This is done by adding a line + like this to ``/etc/inittab`` (exact syntax depends on your getty):: + + S1:23:respawn:/sbin/getty -L ttyS1 9600 vt100 + +5. Init and ``/etc/ioctl.save`` + + Sysvinit remembers its stty settings in a file in ``/etc``, called + ``/etc/ioctl.save``. REMOVE THIS FILE before using the serial + console for the first time, because otherwise init will probably + set the baudrate to 38400 (baudrate of the virtual console). + +6. ``/dev/console`` and X + Programs that want to do something with the virtual console usually + open ``/dev/console``. If you have created the new ``/dev/console`` device, + and your console is NOT the virtual console some programs will fail. + Those are programs that want to access the VT interface, and use + ``/dev/console instead of /dev/tty0``. Some of those programs are:: + + Xfree86, svgalib, gpm, SVGATextMode + + It should be fixed in modern versions of these programs though. + + Note that if you boot without a ``console=`` option (or with + ``console=/dev/tty0``), ``/dev/console`` is the same as ``/dev/tty0``. + In that case everything will still work. + +7. Thanks + + Thanks to Geert Uytterhoeven <geert@linux-m68k.org> + for porting the patches from 2.1.4x to 2.1.6x for taking care of + the integration of these patches into m68k, ppc and alpha. + +Miquel van Smoorenburg <miquels@cistron.nl>, 11-Jun-2000 |