console − multiple device system console

{
"console",_nulldev,_nulldev,
_pconsstrategy, _nulldev,_pconsioctl,
DTTYPE_CHAR,
DTFS_NONE,"pseudo console"
}
is the device name for a pseudo-device that represents the currently
enabled console devices (see
The
device allows multiple devices to function simultaneous as the system
console.  Console input is accepted from all enabled devices, console
output goes to all enabled devices.
The set of console initially enabled is controlled by the environment
variable
If the first letter of $console is "a" or "r", both tty(0) and tty(1)
are enabled, otherwise only tty(0) is enabled.
The
device is primarily useful to allow remote system debugging.
The
device supports the following ioctl’s:
is a character pointer to a null-terminated string giving the name
of a device.  That device is added to the list of currently
enabled console devices.
is a character pointer to a null-terminated string giving the name
of a device.  That device is removed from the list of currently
enabled console devices.
Display on console output the list of currently enabled console devices.
Any other ioctl’s given to the
device are passed on to the currently enabled console devices.
The following diagnostics are issued by the
device:
can’t open %s
A device specified by a PIOCENABLE or PIOCDISABLE
ioctl could not be opened
%s is not a char device
A device specified by a PIOCENABLE ioctl is not appropriate as a
console device
%s is already enabled
A device specified by a PIOCENABLE ioctl is currently enabled
%s not enable
A device specified by a PIOCDISABLE ioctl is not currently enabled
too many consoles enabled
An attempt has been made to enable more devices via PIOCENABLE than
are currently supported
by the
device driver
enable(1spp), tty(4spp)