Documentation for console selection.

share/man/man4/man4.i386/console.4

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+.Dd September 30, 1997
+.Os
+.Dt CONS 4 i386
+.Sh NAME
+.Nm console
+.Nd i386 console interface
+
+.Sh DESCRIPTION
+The
+.Dq console
+device is used for
+.Em kernel printf
+messages and accesses to the
+.Pa /dev/console
+character special device in user mode.
+It is attached to a hardware interface at boot time controlled by options
+in the kernel configuration file or information passed by the boot loader.
+The current choices are:
+.Bl -tag -width aaa
+.It - the standard PC keyboard and display
+(with either the
+.Dq pc
+or the
+.Xr pcvt 4
+driver)
+.It - standard PC serial ports
+(with
+.Xr com 4
+driver)
+.El
+
+.Pp
+The available
+.Em kernel configuration
+options are:
+.Bl -ohang
+.It Cd options CONSDEVNAME=string
+specifies the name of the console device. Valid values are
+.Dq pc
+for the pc keyboard / display (default)
+and
+.Dq com
+for a serial port.
+.It Cd options CONADDR=integer
+sets the base address for the serial console port (default: 0x3f8).
+.It Cd options CONSPEED=integer
+sets the baudrate for the serial console (default: 9600).
+.It Cd options CONS_OVERRIDE
+causes console information passed bt the bootloader to be ignored and
+the settings specified by the three options above (or the defaults) to be
+used. Default behaviour is to use the settings from the bootloader if
+present, and to use option / default values only if no information was
+passed.
+.It Cd options CONMODE=integer
+allows to specify terminal control flags. The argument is a
+.Dq cflag
+value, see
+.Xr termios 4
+for details. Default is
+.Li (CREAD | CS8 | HUPCL)
+(8N1).
+This option takes always effect, because mode settings are not passed
+by the bootloader.
+.El
+
+.Sh EXAMPLES
+.Cd options \&"CONSDEVNAME=\e"com\e"",CONADDR=0x2f8,CONSPEED=19200
+
+.Sh FILES
+.Bl -tag -width /dev/console
+.It Pa /dev/console
+.It Pa /sys/arch/i386/conf/CONFIG
+.El
+
+.Sh SEE ALSO
+.Xr tty 4 ,
+.Xr boot 8
+
+.Sh BUGS
+The console device is chosen early in system startup regardless
+if the specified driver / device is present in the system configuration file.
+If the driver asked for by the bootloader or
+.Dq Cd options CONSDEVNAME
+is not configured into the system, a panic is caused. Because there is
+no console device, no explaining message will be printed.
+If the driver is present, but the specific device instance not, kernel
+printf will work, but
+.Pa /dev/console
+becomes a dummy.