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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
+ options: depend on the driver. For the serial port this
+ defines the baudrate/parity/bits of the port,
+ in the format BBBBPN, where BBBB is the speed,
+ P is parity (n/o/e), and N is bits. 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.
+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