Fatal server error:
(EE) parse_vt_settings: Cannot open /dev/tty0 (Permission denied)
-> edit /etc/X11/Xwrapper.config as per https://unix.stackexchange.com/questions/246508
startx yields this error
/usr/lib/xorg/Xorg.wrap: Only console users are allowed to run the X server
when called from a tmux session, but not from a tty.
-> Edit /etc/X11/Xwrapper.config and set allowed_users=anybody
https://wiki.archlinux.org/index.php/getty#Automatic_login_to_virtual_console
Note: on Debian agetty is located on /sbin/agetty, not /usr/bin/agetty.