1 .. _serial_console:
2
3 Linux Serial Console
4 ====================
5
6 To use a serial port as console you need to co
7 kernel - by default it is not compiled in. For
8 it's the config option next to menu option:
9
10 :menuselection:`Character devices --> Serial d
11
12 You must compile serial support into the kerne
13
14 It is possible to specify multiple devices for
15 define a new kernel command line option to sel
16 use for console output.
17
18 The format of this option is::
19
20 console=device,options
21
22 device: tty0 for the foregroun
23 ttyX for any other vir
24 ttySx for a serial por
25 lp0 for the first para
26 ttyUSB0 for the first
27
28 options: depend on the driver.
29 defines the baudrate/p
30 the port, in the forma
31 speed, P is parity (n/
32 and F is flow control
33 9600n8. The maximum ba
34
35 You can specify multiple console= options on t
36
37 The behavior is well defined when each device
38 In this case, the output will appear on all re
39 the last device will be used when you open ``/
40 So, for example::
41
42 console=ttyS1,9600 console=tty0
43
44 defines that opening ``/dev/console`` will get
45 virtual console, and kernel messages will appe
46 console and the 2nd serial port (ttyS1 or COM2
47
48 The behavior is more complicated when the same
49 times. In this case, there are the following t
50
51 1. The output will appear only on the first de
52
53 2. ``/dev/console`` will be associated with th
54 Where the registration order depends on how
55 subsystems.
56
57 This rule is used also when the last consol
58 for other reasons. For example, because of
59 the hardware is not available.
60
61 The result might be surprising. For example, t
62 lines have the same result::
63
64 console=ttyS1,9600 console=tty0 consol
65 console=tty0 console=ttyS1,9600 consol
66
67 The kernel messages are printed only on ``tty0
68 ``/dev/console`` gets associated with ``tty0``
69 tries to register graphical consoles before se
70 because of the default behavior when no consol
71 see below.
72
73 Note that the last ``console=tty1`` parameter
74 The kernel command line is used also by system
75 defined ``tty1`` as the login console.
76
77 If no console device is specified, the first d
78 acting as a system console will be used. At th
79 first looks for a VGA card and then for a seri
80 have a VGA card in your system the first seria
81 become the console.
82
83 You will need to create a new device to use ``
84 ``/dev/console`` is now character device 5,1.
85
86 (You can also use a network device as a consol
87 ``Documentation/networking/netconsole.rst`` fo
88
89 Here's an example that will use ``/dev/ttyS1``
90 Replace the sample values as needed.
91
92 1. Create ``/dev/console`` (real console) and
93 console)::
94
95 cd /dev
96 rm -f console tty0
97 mknod -m 622 console c 5 1
98 mknod -m 622 tty0 c 4 0
99
100 2. LILO can also take input from a serial devi
101 useful option. To tell LILO to use the seri
102 In lilo.conf (global section)::
103
104 serial = 1,9600n8 (ttyS1, 9600 bd, no pa
105
106 3. Adjust to kernel flags for the new kernel,
107 again in lilo.conf (kernel section)::
108
109 append = "console=ttyS1,9600"
110
111 4. Make sure a getty runs on the serial port s
112 it once the system is done booting. This is
113 like this to ``/etc/inittab`` (exact syntax
114
115 S1:23:respawn:/sbin/getty -L ttyS1 9600 v
116
117 5. Init and ``/etc/ioctl.save``
118
119 Sysvinit remembers its stty settings in a f
120 ``/etc/ioctl.save``. REMOVE THIS FILE befor
121 console for the first time, because otherwi
122 set the baudrate to 38400 (baudrate of the
123
124 6. ``/dev/console`` and X
125 Programs that want to do something with the
126 open ``/dev/console``. If you have created
127 and your console is NOT the virtual console
128 Those are programs that want to access the
129 ``/dev/console instead of /dev/tty0``. Some
130
131 Xfree86, svgalib, gpm, SVGATextMode
132
133 It should be fixed in modern versions of th
134
135 Note that if you boot without a ``console=`
136 ``console=/dev/tty0``), ``/dev/console`` is
137 In that case everything will still work.
138
139 7. Thanks
140
141 Thanks to Geert Uytterhoeven <geert@linux-m6
142 for porting the patches from 2.1.4x to 2.1.
143 the integration of these patches into m68k,
144
145 Miquel van Smoorenburg <miquels@cistron.nl>, 11
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