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- 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/
- Sysvinit remembers its stty settings in a file in /etc, called
- `/etc/'. 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