I found a similar problem at 1404 . if set console=ttys0 in cmdline , VT ioctls will fail and can't switch user(Can't log in the original user) .
At 2016-04-04 13:05:44, "Robert Ancell" <firstname.lastname@example.org> wrote:
--Robert- What is the correct way to do these VT calls? Every time i try and work this out there seems to be no documentation anywhere and reading the kernel leaves me more confused.- Does anyone know what has changed that means these no longer work?Two questions:Hi all,I've noticed in Xenial that VT ioctls that LightDM is using (VT_GETSTATE, VT_ACTIVATE, VT_WAITACTIVE) on /dev/console now seem to be failing (errno 5 - Input/output error). If I switch to /dev/tty0 they seem to work (this is what GDM and logind are using).