mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-12-21 08:46:49 +07:00
f1a1c2dc2a
Add info on flow control for serial consoles. Refer to netconsole option also. Signed-off-by: Randy Dunlap <rdunlap@xenotime.net> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
110 lines
4.0 KiB
Plaintext
110 lines
4.0 KiB
Plaintext
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/ioctl.save
|
|
|
|
Sysvinit remembers its stty settings in a file in /etc, called
|
|
`/etc/ioctl.save'. 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 <geert@linux-m68k.org>
|
|
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 <miquels@cistron.nl>, 11-Jun-2000
|