我最近全新安装了 Ubuntu 19.04。从那时起，当我启动机器时，我会看到一个显示启动日志的屏幕，但不会切换到登录屏幕。
我可以通过按 [CTRL][ALT][F2] 然后按 [CTRL][ALT][F1] 来手动启动登录屏幕。
我怎样才能让登录屏幕自动出现？
启动日志（来自 /var/log/boot.log，但与我在启动期间看到的内容相符）是：
[ OK ] Started Tell Plymouth To Write Out Runtime Data.
[ OK ] Reached target System Initialization.
[ OK ] Started Discard unused blocks once a week.
[ OK ] Started CUPS Scheduler.
[ OK ] Started Trigger anacron every hour.
[ OK ] Listening on Activation socket for spice guest agent daemon.
Starting Socket activation for snappy daemon.
[ OK ] Listening on ACPID Listen Socket.
[ OK ] Started Daily rotation of log files.
[ OK ] Started Daily man-db regeneration.
[ OK ] Listening on UUID daemon activation socket.
[ OK ] Started ACPI Events Check.
[ OK ] Reached target Paths.
[ OK ] Started Message of the Day.
[ OK ] Listening on D-Bus System Message Bus Socket.
[ OK ] Listening on Avahi mDNS/DNS-SD Stack Activation Socket.
[ OK ] Started Daily Cleanup of Temporary Directories.
[ OK ] Listening on CUPS Scheduler.
[ OK ] Started Daily apt download activities.
[ OK ] Started Daily apt upgrade and clean activities.
[ OK ] Reached target Timers.
[ OK ] Listening on Socket activation for snappy daemon.
[ OK ] Reached target Sockets.
[ OK ] Reached target Basic System.
Starting Accounts Service...
Starting LSB: Record successful boot for GRUB...
Starting Avahi mDNS/DNS-SD Stack...
[ OK ] Started ACPI event daemon.
Starting Disk Manager...
[ OK ] Started irqbalance daemon.
Starting Switcheroo Control Proxy service...
Starting Bluetooth service...
Starting Rotate log files...
Starting Login Service...
[ OK ] Started Run anacron jobs.
Starting LSB: automatic crash report generation...
Starting Dispatcher daemon for systemd-networkd...
[ OK ] Reached target Login Prompts.
[ OK ] Started Save initial kernel messages after boot.
Starting Detect the available GPUs and deal with any system changes...
[ OK ] Reached target Sound Card.
Starting System Logging Service...
Starting Modem Manager...
Starting Daily man-db regeneration...
[ OK ] Started D-Bus System Message Bus.
Starting Network Manager...
Starting WPA supplicant...
[ OK ] Started Regular background program processing daemon.
Starting Configure Plugged-In Printer...
Starting Thermal Daemon Service...
[ OK ] Started CUPS Scheduler.
[ OK ] Reached target Printer.
Starting Restore /etc/resolv.conf if the system crashed before the ppp link was shut down...
[ OK ] Started Set the CPU Frequency Scaling governor.
Starting Snappy daemon...
[ OK ] Started Switcheroo Control Proxy service.
[ OK ] Started Restore /etc/resolv.conf if the system crashed before the ppp link was shut down.
[ OK ] Started Login Service.
[ OK ] Started LSB: Record successful boot for GRUB.
[ OK ] Started LSB: automatic crash report generation.
[ OK ] Started Detect the available GPUs and deal with any system changes.
[ OK ] Started Bluetooth service.
[ OK ] Started WPA supplicant.
[ OK ] Started Thermal Daemon Service.
[ OK ] Started System Logging Service.
[ OK ] Started Avahi mDNS/DNS-SD Stack.
[ OK ] Started Make remote CUPS printers available locally.
Starting Manage, Install and Generate Color Profiles...
[ OK ] Reached target Bluetooth.
Starting Authorization Manager...
[ OK ] Started Dispatcher daemon for systemd-networkd.
Starting Hostname Service...
[ OK ] Started Authorization Manager.
[ OK ] Started Hostname Service.
[ OK ] Started Manage, Install and Generate Color Profiles.
[ OK ] Started Network Manager.
Starting Network Manager Wait Online...
[ OK ] Reached target Network.
Starting Permit User Sessions...
Starting OpenVPN service...
[ OK ] Started Unattended Upgrades Shutdown.
[ OK ] Started OpenVPN service.
Stopping CUPS Scheduler...
[ OK ] Stopped CUPS Scheduler.
[ OK ] Started CUPS Scheduler.
[ OK ] Started Permit User Sessions.
Starting GNOME Display Manager...
Starting Hold until boot process finishes up...
Starting Network Manager Script Dispatcher Service...
[ OK ] Started Network Manager Script Dispatcher Service.
[ OK ] Started Modem Manager.
[ OK ] Started GNOME Display Manager.