Contents of /alx-src/tags/kernel26-2.6.12-alx-r9/Documentation/serial-console.txt
Parent Directory | Revision Log
Revision 630 -
(show annotations)
(download)
Wed Mar 4 11:03:09 2009 UTC (15 years, 6 months ago) by niro
File MIME type: text/plain
File size: 3915 byte(s)
Wed Mar 4 11:03:09 2009 UTC (15 years, 6 months ago) by niro
File MIME type: text/plain
File size: 3915 byte(s)
Tag kernel26-2.6.12-alx-r9
1 | Linux Serial Console |
2 | |
3 | To use a serial port as console you need to compile the support into your |
4 | kernel - by default it is not compiled in. For PC style serial ports |
5 | it's the config option next to "Standard/generic (dumb) serial support". |
6 | You must compile serial support into the kernel and not as a module. |
7 | |
8 | It is possible to specify multiple devices for console output. You can |
9 | define a new kernel command line option to select which device(s) to |
10 | use for console output. |
11 | |
12 | The format of this option is: |
13 | |
14 | console=device,options |
15 | |
16 | device: tty0 for the foreground virtual console |
17 | ttyX for any other virtual console |
18 | ttySx for a serial port |
19 | lp0 for the first parallel port |
20 | |
21 | options: depend on the driver. For the serial port this |
22 | defines the baudrate/parity/bits of the port, |
23 | in the format BBBBPN, where BBBB is the speed, |
24 | P is parity (n/o/e), and N is bits. Default is |
25 | 9600n8. The maximum baudrate is 115200. |
26 | |
27 | You can specify multiple console= options on the kernel command line. |
28 | Output will appear on all of them. The last device will be used when |
29 | you open /dev/console. So, for example: |
30 | |
31 | console=ttyS1,9600 console=tty0 |
32 | |
33 | defines that opening /dev/console will get you the current foreground |
34 | virtual console, and kernel messages will appear on both the VGA |
35 | console and the 2nd serial port (ttyS1 or COM2) at 9600 baud. |
36 | |
37 | Note that you can only define one console per device type (serial, video). |
38 | |
39 | If no console device is specified, the first device found capable of |
40 | acting as a system console will be used. At this time, the system |
41 | first looks for a VGA card and then for a serial port. So if you don't |
42 | have a VGA card in your system the first serial port will automatically |
43 | become the console. |
44 | |
45 | You will need to create a new device to use /dev/console. The official |
46 | /dev/console is now character device 5,1. |
47 | |
48 | Here's an example that will use /dev/ttyS1 (COM2) as the console. |
49 | Replace the sample values as needed. |
50 | |
51 | 1. Create /dev/console (real console) and /dev/tty0 (master virtual |
52 | console): |
53 | |
54 | cd /dev |
55 | rm -f console tty0 |
56 | mknod -m 622 console c 5 1 |
57 | mknod -m 622 tty0 c 4 0 |
58 | |
59 | 2. LILO can also take input from a serial device. This is a very |
60 | useful option. To tell LILO to use the serial port: |
61 | In lilo.conf (global section): |
62 | |
63 | serial = 1,9600n8 (ttyS1, 9600 bd, no parity, 8 bits) |
64 | |
65 | 3. Adjust to kernel flags for the new kernel, |
66 | again in lilo.conf (kernel section) |
67 | |
68 | append = "console=ttyS1,9600" |
69 | |
70 | 4. Make sure a getty runs on the serial port so that you can login to |
71 | it once the system is done booting. This is done by adding a line |
72 | like this to /etc/inittab (exact syntax depends on your getty): |
73 | |
74 | S1:23:respawn:/sbin/getty -L ttyS1 9600 vt100 |
75 | |
76 | 5. Init and /etc/ioctl.save |
77 | |
78 | Sysvinit remembers its stty settings in a file in /etc, called |
79 | `/etc/ioctl.save'. REMOVE THIS FILE before using the serial |
80 | console for the first time, because otherwise init will probably |
81 | set the baudrate to 38400 (baudrate of the virtual console). |
82 | |
83 | 6. /dev/console and X |
84 | Programs that want to do something with the virtual console usually |
85 | open /dev/console. If you have created the new /dev/console device, |
86 | and your console is NOT the virtual console some programs will fail. |
87 | Those are programs that want to access the VT interface, and use |
88 | /dev/console instead of /dev/tty0. Some of those programs are: |
89 | |
90 | Xfree86, svgalib, gpm, SVGATextMode |
91 | |
92 | It should be fixed in modern versions of these programs though. |
93 | |
94 | Note that if you boot without a console= option (or with |
95 | console=/dev/tty0), /dev/console is the same as /dev/tty0. In that |
96 | case everything will still work. |
97 | |
98 | 7. Thanks |
99 | |
100 | Thanks to Geert Uytterhoeven <geert@linux-m68k.org> |
101 | for porting the patches from 2.1.4x to 2.1.6x for taking care of |
102 | the integration of these patches into m68k, ppc and alpha. |
103 | |
104 | Miquel van Smoorenburg <miquels@cistron.nl>, 11-Jun-2000 |