From 849369d6c66d3054688672f97d31fceb8e8230fb Mon Sep 17 00:00:00 2001 From: root Date: Fri, 25 Dec 2015 04:40:36 +0000 Subject: initial_commit --- Documentation/serial-console.txt | 109 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 109 insertions(+) create mode 100644 Documentation/serial-console.txt (limited to 'Documentation/serial-console.txt') diff --git a/Documentation/serial-console.txt b/Documentation/serial-console.txt new file mode 100644 index 00000000..9a7bc8b3 --- /dev/null +++ b/Documentation/serial-console.txt @@ -0,0 +1,109 @@ + 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 "Standard/generic (dumb) serial support". +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 + 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 , 11-Jun-2000 -- cgit v1.2.3