^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 1) .. _serial_console:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 2)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 3) Linux Serial Console
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 4) ====================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 5)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 6) To use a serial port as console you need to compile the support into your
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 7) kernel - by default it is not compiled in. For PC style serial ports
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 8) it's the config option next to menu option:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 9)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 10) :menuselection:`Character devices --> Serial drivers --> 8250/16550 and compatible serial support --> Console on 8250/16550 and compatible serial port`
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 11)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 12) You must compile serial support into the kernel and not as a module.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 13)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 14) It is possible to specify multiple devices for console output. You can
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 15) define a new kernel command line option to select which device(s) to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 16) use for console output.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 17)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 18) The format of this option is::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 19)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 20) console=device,options
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 21)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 22) device: tty0 for the foreground virtual console
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 23) ttyX for any other virtual console
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 24) ttySx for a serial port
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 25) lp0 for the first parallel port
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 26) ttyUSB0 for the first USB serial device
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 27)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 28) options: depend on the driver. For the serial port this
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 29) defines the baudrate/parity/bits/flow control of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 30) the port, in the format BBBBPNF, where BBBB is the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 31) speed, P is parity (n/o/e), N is number of bits,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 32) and F is flow control ('r' for RTS). Default is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 33) 9600n8. The maximum baudrate is 115200.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 34)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 35) You can specify multiple console= options on the kernel command line.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 36) Output will appear on all of them. The last device will be used when
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 37) you open ``/dev/console``. So, for example::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 38)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 39) console=ttyS1,9600 console=tty0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 40)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 41) defines that opening ``/dev/console`` will get you the current foreground
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 42) virtual console, and kernel messages will appear on both the VGA
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 43) console and the 2nd serial port (ttyS1 or COM2) at 9600 baud.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 44)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 45) Note that you can only define one console per device type (serial, video).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 46)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 47) If no console device is specified, the first device found capable of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 48) acting as a system console will be used. At this time, the system
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 49) first looks for a VGA card and then for a serial port. So if you don't
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 50) have a VGA card in your system the first serial port will automatically
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 51) become the console.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 52)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 53) You will need to create a new device to use ``/dev/console``. The official
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 54) ``/dev/console`` is now character device 5,1.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 55)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 56) (You can also use a network device as a console. See
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 57) ``Documentation/networking/netconsole.rst`` for information on that.)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 58)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 59) Here's an example that will use ``/dev/ttyS1`` (COM2) as the console.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 60) Replace the sample values as needed.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 61)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 62) 1. Create ``/dev/console`` (real console) and ``/dev/tty0`` (master virtual
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 63) console)::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 64)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 65) cd /dev
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 66) rm -f console tty0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 67) mknod -m 622 console c 5 1
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 68) mknod -m 622 tty0 c 4 0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 69)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 70) 2. LILO can also take input from a serial device. This is a very
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 71) useful option. To tell LILO to use the serial port:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 72) In lilo.conf (global section)::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 73)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 74) serial = 1,9600n8 (ttyS1, 9600 bd, no parity, 8 bits)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 75)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 76) 3. Adjust to kernel flags for the new kernel,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 77) again in lilo.conf (kernel section)::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 78)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 79) append = "console=ttyS1,9600"
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 80)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 81) 4. Make sure a getty runs on the serial port so that you can login to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 82) it once the system is done booting. This is done by adding a line
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 83) like this to ``/etc/inittab`` (exact syntax depends on your getty)::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 84)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 85) S1:23:respawn:/sbin/getty -L ttyS1 9600 vt100
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 86)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 87) 5. Init and ``/etc/ioctl.save``
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 88)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 89) Sysvinit remembers its stty settings in a file in ``/etc``, called
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 90) ``/etc/ioctl.save``. REMOVE THIS FILE before using the serial
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 91) console for the first time, because otherwise init will probably
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 92) set the baudrate to 38400 (baudrate of the virtual console).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 93)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 94) 6. ``/dev/console`` and X
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 95) Programs that want to do something with the virtual console usually
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 96) open ``/dev/console``. If you have created the new ``/dev/console`` device,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 97) and your console is NOT the virtual console some programs will fail.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 98) Those are programs that want to access the VT interface, and use
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 99) ``/dev/console instead of /dev/tty0``. Some of those programs are::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 100)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 101) Xfree86, svgalib, gpm, SVGATextMode
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 102)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 103) It should be fixed in modern versions of these programs though.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 104)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 105) Note that if you boot without a ``console=`` option (or with
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 106) ``console=/dev/tty0``), ``/dev/console`` is the same as ``/dev/tty0``.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 107) In that case everything will still work.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 108)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 109) 7. Thanks
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 110)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 111) Thanks to Geert Uytterhoeven <geert@linux-m68k.org>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 112) for porting the patches from 2.1.4x to 2.1.6x for taking care of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 113) the integration of these patches into m68k, ppc and alpha.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 114)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 115) Miquel van Smoorenburg <miquels@cistron.nl>, 11-Jun-2000
Orange Pi5 kernel
Deprecated Linux kernel 5.10.110 for OrangePi 5/5B/5+ boards
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