What appears to be happening is the greeter is not aware it is running
inside Unity System Compositor and so it trying to directly access the
video drivers. This fails because it is not running as root.
The cause seems to be LightDM is setting MIR_SOCKET to the name of the
U-S-C socket but this no longer works (possibly due to a change in bug
1290345).
The solution is to set MIR_SERVER_HOST_SOCKET instead, which is the
recommended/correct variable to tell a Mir server the socket of the
parent server (U-S-C in this case) to connect to.
** Also affects: lightdm (Ubuntu)
Importance: Undecided
Status: New
** Changed in: lightdm
Importance: Undecided => High
** Changed in: lightdm (Ubuntu)
Importance: Undecided => High
** Changed in: lightdm (Ubuntu)
Assignee: (unassigned) => Robert Ancell (robert-ancell)
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Touch seeded packages, which is subscribed to lightdm in Ubuntu.
https://bugs.launchpad.net/bugs/1583624
Title:
Mir cannot open a tty when started by lightdm
Status in Light Display Manager:
In Progress
Status in Light Display Manager 1.18 series:
In Progress
Status in lightdm package in Ubuntu:
Triaged
Status in lightdm source package in Xenial:
Triaged
Bug description:
From mir-greeter.log (and with minor instrumentation from RAOF)
ERROR: QMirServer - Mir failed to start
qtmir.screens: ScreenController::ScreenController
qtmir.mir: MirServer created
qtmir.mir: Command line arguments passed to Qt: ("/usr/bin/unity8",
"--mode=greeter")
ERROR:
/home/josh/Documents/mir/verbose-error-for-vt-finding/src/server/graphics/default_configuration.cpp(133):
Throw in function
mir::DefaultServerConfiguration::the_graphics_platform()::<lambda()>
Dynamic exception type:
boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<std::runtime_error>
>
std::exception::what: Exception while creating graphics platform
ERROR:
/home/josh/Documents/mir/verbose-error-for-vt-finding/src/platforms/mesa/server/kms/linux_virtual_terminal.cpp(238):
Throw in function int
mir::graphics::mesa::LinuxVirtualTerminal::find_active_vt_number()
Dynamic exception type:
boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<std::runtime_error>
>
std::exception::what: Failed to find the current VT. Tried:
/dev/tty0:
Failed to open read-only: Permission denied
Failed to open write-only: Permission denied
/dev/tty:
Failed to open read-only: No such device or address
Failed to open write-only: No such device or address
This occurs when trying to start the unity8 greeter under unity system
compositor
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