Linux – How to change the default TTY after boot

You can use the command dmesg -n1 to prevent all messages, except panic messages, from appearing on the console.

To make this change permanent, modify your /etc/sysctl.conf file to include the following setting (the first 3 is the important part).

kernel.printk = 3 4 1 3

See this post for information on the kernel.printk values.

The man page for tty_ioctl lists the ioctl TIOCCONS. When applied to an open file descriptor of a tty it will redirect future output intended for /dev/console to that tty.

You can use this in a simple perl script. Create and chmod +x a file mysetconsole holding the following:

#!/usr/bin/perl
# https://unix.stackexchange.com/a/397790/119298
# see man tty_ioctl for TIOCCONS
# and perldoc IO::Tty::Constant
require "sys/ioctl.ph";
use IO::Tty::Constant qw(TIOCCONS);
ioctl(STDIN,TIOCCONS,0) or die $!;

Assuming you can open the wanted device, use it simply as

sudo ./mysetconsole </dev/ttys3

You will not be able to use it again until you set the console back to /dev/console, with

sudo sh -c './mysetconsole </dev/console'

You may get perl warnings about _FORTIFY_SOURCE which can be ignored. You will need rpm package perl-IO-Tty or debian package libio-pty-perl. If you prefer you can just look for the definition of TIOCCONS in the system include files. I found mine in:

/usr/include/asm-generic/ioctls.h: #define TIOCCONS      0x541D

Your perl script can then just be

#!/usr/bin/perl
# https://unix.stackexchange.com/a/397790/119298
sub TIOCCONS{ return 0x541D; }
ioctl(STDIN,TIOCCONS(),0) or die $!;