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