1.. _serial_console: 2 3Linux Serial Console 4==================== 5 6To use a serial port as console you need to compile the support into your 7kernel - by default it is not compiled in. For PC style serial ports 8it's the config option next to menu option: 9 10:menuselection:`Character devices --> Serial drivers --> 8250/16550 and compatible serial support --> Console on 8250/16550 and compatible serial port` 11 12You must compile serial support into the kernel and not as a module. 13 14It is possible to specify multiple devices for console output. You can 15define a new kernel command line option to select which device(s) to 16use for console output. 17 18The format of this option is:: 19 20 console=device,options 21 22 device: tty0 for the foreground virtual console 23 ttyX for any other virtual console 24 ttySx for a serial port 25 lp0 for the first parallel port 26 ttyUSB0 for the first USB serial device 27 28 options: depend on the driver. For the serial port this 29 defines the baudrate/parity/bits/flow control of 30 the port, in the format BBBBPNF, where BBBB is the 31 speed, P is parity (n/o/e), N is number of bits, 32 and F is flow control ('r' for RTS). Default is 33 9600n8. The maximum baudrate is 115200. 34 35You can specify multiple console= options on the kernel command line. 36Output will appear on all of them. The last device will be used when 37you open ``/dev/console``. So, for example:: 38 39 console=ttyS1,9600 console=tty0 40 41defines that opening ``/dev/console`` will get you the current foreground 42virtual console, and kernel messages will appear on both the VGA 43console and the 2nd serial port (ttyS1 or COM2) at 9600 baud. 44 45Note that you can only define one console per device type (serial, video). 46 47If no console device is specified, the first device found capable of 48acting as a system console will be used. At this time, the system 49first looks for a VGA card and then for a serial port. So if you don't 50have a VGA card in your system the first serial port will automatically 51become the console. 52 53You will need to create a new device to use ``/dev/console``. The official 54``/dev/console`` is now character device 5,1. 55 56(You can also use a network device as a console. See 57``Documentation/networking/netconsole.rst`` for information on that.) 58 59Here's an example that will use ``/dev/ttyS1`` (COM2) as the console. 60Replace the sample values as needed. 61 621. Create ``/dev/console`` (real console) and ``/dev/tty0`` (master virtual 63 console):: 64 65 cd /dev 66 rm -f console tty0 67 mknod -m 622 console c 5 1 68 mknod -m 622 tty0 c 4 0 69 702. LILO can also take input from a serial device. This is a very 71 useful option. To tell LILO to use the serial port: 72 In lilo.conf (global section):: 73 74 serial = 1,9600n8 (ttyS1, 9600 bd, no parity, 8 bits) 75 763. Adjust to kernel flags for the new kernel, 77 again in lilo.conf (kernel section):: 78 79 append = "console=ttyS1,9600" 80 814. Make sure a getty runs on the serial port so that you can login to 82 it once the system is done booting. This is done by adding a line 83 like this to ``/etc/inittab`` (exact syntax depends on your getty):: 84 85 S1:23:respawn:/sbin/getty -L ttyS1 9600 vt100 86 875. Init and ``/etc/ioctl.save`` 88 89 Sysvinit remembers its stty settings in a file in ``/etc``, called 90 ``/etc/ioctl.save``. REMOVE THIS FILE before using the serial 91 console for the first time, because otherwise init will probably 92 set the baudrate to 38400 (baudrate of the virtual console). 93 946. ``/dev/console`` and X 95 Programs that want to do something with the virtual console usually 96 open ``/dev/console``. If you have created the new ``/dev/console`` device, 97 and your console is NOT the virtual console some programs will fail. 98 Those are programs that want to access the VT interface, and use 99 ``/dev/console instead of /dev/tty0``. Some of those programs are:: 100 101 Xfree86, svgalib, gpm, SVGATextMode 102 103 It should be fixed in modern versions of these programs though. 104 105 Note that if you boot without a ``console=`` option (or with 106 ``console=/dev/tty0``), ``/dev/console`` is the same as ``/dev/tty0``. 107 In that case everything will still work. 108 1097. Thanks 110 111 Thanks to Geert Uytterhoeven <geert@linux-m68k.org> 112 for porting the patches from 2.1.4x to 2.1.6x for taking care of 113 the integration of these patches into m68k, ppc and alpha. 114 115Miquel van Smoorenburg <miquels@cistron.nl>, 11-Jun-2000 116