使用 KDE Plasma。
当我尝试登录时，我可以看到之前打开的所有窗口和背景（没有图标，没有热键栏）。有时图标会弹出一秒钟，然后背景变黑。除了似乎Ctrl+Alt+Delete可以使用的热键外，没有其他热键。
在终端创建了一个新用户，无法登录（返回登录屏幕）。
我认为我没有改变任何东西，只是重启后才发生的。
由于我没有有效的互联网连接（没有 KDE 似乎无法启动 NetworkManager），所以我无法重新安装 xorg 和 kde。
系统原先是Kubuntu 17.10，升级到18.04
lsb_release：
Distributor ID: Ubuntu
Description: Ubuntu 18.04.4 LTS
Release: 18.04
Codename: bionic
启动目录：
$DISPLAY is not set or cannot connect to the X server.
启动：
/usr/lib/xorg/Xorg.wrap: Only console users are allowed to run the X server
xinit: giving up
xinit: unable to connect to X server: Connection refused
xinit: server error
Dateideskriptor, der auf die Konsole verweist, konnte nicht gefunden werden.
最后一行：File descriptor that points to terminal could not be found.
初始化：
/usr/lib/xorg/Xorg.wrap: Only console users are allowed to run the X server
XIO: fatal IO error 11 (Resource temporarily unavailable) on X server ":0"
after 7 requests (7 known processed) with 0 events remaining.
等离子壳：
qt.qpa.screen: QXcbConnection: Could not connect to display
Could not connect to any X display.
日志控制：
Apr 15 16:14:32 PiW04x acpid[1332]: 1 client rule loaded
Apr 15 16:14:33 PiW04x dbus-daemon[1942]: [session uid=1001 pid=1940] Activating service name='org.freedesktop.Notifications' requested by ':1.28' (uid=1001 pid=2046 comm="kwin_x11 -session 1084e157300001584601376000000215" label="unconfined")
Apr 15 16:14:34 PiW04x systemd[1]: Started Getty on tty2.
Apr 15 16:14:35 PiW04x acpid[1332]: client 1529[0:0] has disconnected
Apr 15 16:14:35 PiW04x acpid[1332]: client connected from 1529[0:0]
Apr 15 16:14:35 PiW04x acpid[1332]: 1 client rule loaded
Apr 15 16:14:39 PiW04x polkitd(authority=local)[1446]: Unregistered Authentication Agent for unix-session:3 (system bus name :1.60, object path /org/kde/PolicyKit1/AuthenticationAgent, locale de_AT.UTF-8)
Apr 15 16:14:39 PiW04x sddm[1526]: kwalletd5: Checking for pam module
Apr 15 16:14:39 PiW04x sddm[1526]: kwalletd5: Got pam-login param
Apr 15 16:14:39 PiW04x sddm[1526]: kwalletd5: Waiting for hash on 15-
Apr 15 16:14:39 PiW04x sddm[1526]: kwalletd5: waitingForEnvironment on: 3
Apr 15 16:14:39 PiW04x sddm[1526]: kwalletd5: client connected
Apr 15 16:14:39 PiW04x sddm[1526]: kwalletd5: client disconnected
Apr 15 16:14:40 PiW04x sddm-helper[1889]: [PAM] Closing session
Apr 15 16:14:40 PiW04x sddm-helper[1889]: pam_unix(sddm:session): session closed for user const
Apr 15 16:14:40 PiW04x sddm-helper[1889]: pam_kwallet(sddm:session): pam_kwallet: pam_sm_close_session
Apr 15 16:14:40 PiW04x sddm-helper[1889]: pam_kwallet5(sddm:session): pam_kwallet5: pam_sm_close_session
Apr 15 16:14:40 PiW04x sddm-helper[1889]: pam_kwallet(sddm:setcred): pam_kwallet: pam_sm_setcred
Apr 15 16:14:40 PiW04x sddm-helper[1889]: pam_kwallet5(sddm:setcred): pam_kwallet5: pam_sm_setcred
Apr 15 16:14:40 PiW04x sddm-helper[1889]: [PAM] Ended.
Apr 15 16:14:40 PiW04x sddm[1526]: Auth: sddm-helper exited successfully
Apr 15 16:14:40 PiW04x sddm[1526]: Socket server stopping...
Apr 15 16:14:40 PiW04x sddm[1526]: Socket server stopped.
Apr 15 16:14:40 PiW04x sddm[1526]: Display server stopping...
Apr 15 16:14:40 PiW04x org.a11y.Bus[1942]: XIO: fatal IO error 11 (Resource temporarily unavailable) on X server ":0"
Apr 15 16:14:40 PiW04x org.a11y.Bus[1942]: after 45 requests (45 known processed) with 0 events remaining.
Apr 15 16:14:40 PiW04x org.kde.ActivityManager[1942]: The X11 connection broke (error 1). Did the X11 server die?
Apr 15 16:14:40 PiW04x org.kde.ActivityManager[1942]: Closing SQL connection: "kactivities_db_resources_140563586010240_readwrite"
Apr 15 16:14:40 PiW04x org.kde.kuiserver[1942]: The X11 connection broke (error 1). Did the X11 server die?
Apr 15 16:14:40 PiW04x org.kde.kglobalaccel[1942]: The X11 connection broke (error 1). Did the X11 server die?
Apr 15 16:14:40 PiW04x org.kde.KScreen[1942]: The X11 connection broke (error 1). Did the X11 server die?
Apr 15 16:14:40 PiW04x org.gtk.vfs.Daemon[1942]: A connection to the bus can't be made
Apr 15 16:14:40 PiW04x NetworkManager[1433]: <warn> [1586960080.0379] error requesting auth for org.freedesktop.NetworkManager.enable-disable-wwan: Authorization check failed: Failed to open file “/proc/2043/status”: No such file or directory
Apr 15 16:14:40 PiW04x NetworkManager[1433]: <warn> [1586960080.0385] error requesting auth for org.freedesktop.NetworkManager.enable-disable-wimax: Authorization check failed: Failed to open file “/proc/2043/status”: No such file or directory
Apr 15 16:14:40 PiW04x NetworkManager[1433]: <warn> [1586960080.0392] error requesting auth for org.freedesktop.NetworkManager.network-control: Authorization check failed: Failed to open file “/proc/2043/status”: No such file or directory
Apr 15 16:14:40 PiW04x NetworkManager[1433]: <warn> [1586960080.0398] error requesting auth for org.freedesktop.NetworkManager.wifi.share.protected: Authorization check failed: Failed to open file “/proc/2043/status”: No such file or directory
Apr 15 16:14:40 PiW04x org.freedesktop.Tracker1[1942]: Received signal:15->'Beendet'
Apr 15 16:14:40 PiW04x org.freedesktop.Tracker1[1942]: OK
Apr 15 16:14:40 PiW04x NetworkManager[1433]: <warn> [1586960080.0404] error requesting auth for org.freedesktop.NetworkManager.wifi.share.open: Authorization check failed: Failed to open file “/proc/2043/status”: No such file or directory
Apr 15 16:14:40 PiW04x NetworkManager[1433]: <warn> [1586960080.0411] error requesting auth for org.freedesktop.NetworkManager.settings.modify.system: Authorization check failed: Failed to open file “/proc/2043/status”: No such file or directory
Apr 15 16:14:40 PiW04x NetworkManager[1433]: <warn> [1586960080.0417] error requesting auth for org.freedesktop.NetworkManager.settings.modify.own: Authorization check failed: Failed to open file “/proc/2043/status”: No such file or directory
Apr 15 16:14:40 PiW04x NetworkManager[1433]: <warn> [1586960080.0426] error requesting auth for org.freedesktop.NetworkManager.settings.modify.hostname: Authorization check failed: Failed to open file “/proc/2043/status”: No such file or directory
Apr 15 16:14:40 PiW04x NetworkManager[1433]: <warn> [1586960080.0434] error requesting auth for org.freedesktop.NetworkManager.settings.modify.global-dns: Authorization check failed: Failed to open file “/proc/2043/status”: No such file or directory
Apr 15 16:14:40 PiW04x NetworkManager[1433]: <warn> [1586960080.0441] error requesting auth for org.freedesktop.NetworkManager.reload: Authorization check failed: Failed to open file “/proc/2043/status”: No such file or directory
Apr 15 16:14:40 PiW04x NetworkManager[1433]: <warn> [1586960080.0448] error requesting auth for org.freedesktop.NetworkManager.checkpoint-rollback: Authorization check failed: Failed to open file “/proc/2043/status”: No such file or directory
Apr 15 16:14:40 PiW04x NetworkManager[1433]: <warn> [1586960080.0455] error requesting auth for org.freedesktop.NetworkManager.enable-disable-statistics: Authorization check failed: Failed to open file “/proc/2043/status”: No such file or directory
Apr 15 16:14:40 PiW04x NetworkManager[1433]: <warn> [1586960080.0461] error requesting auth for org.freedesktop.NetworkManager.enable-disable-connectivity-check: Authorization check failed: Failed to open file “/proc/2043/status”: No such file or directory
Apr 15 16:14:40 PiW04x sddm[1526]: Display server stopped.
Apr 15 16:14:40 PiW04x sddm[1526]: Running display stop script "/usr/share/sddm/scripts/Xstop"
Apr 15 16:14:40 PiW04x sddm[1526]: Removing display ":0" ...
Apr 15 16:14:40 PiW04x sddm[1526]: Adding new display on vt 1 ...
Apr 15 16:14:40 PiW04x sddm[1526]: Loading theme configuration from ""
Apr 15 16:14:40 PiW04x sddm[1526]: Display server starting...
Apr 15 16:14:40 PiW04x sddm[1526]: Running: /usr/bin/X -nolisten tcp -auth /var/run/sddm/{d02c7274-2c9f-452f-8967-bc8fcc638d42} -background none -noreset -displayfd 19 -seat seat0 vt1
Apr 15 16:14:40 PiW04x acpid[1332]: client 1529[0:0] has disconnected
Apr 15 16:14:40 PiW04x acpid[1332]: client connected from 21486[0:0]
Apr 15 16:14:40 PiW04x acpid[1332]: 1 client rule loaded
Apr 15 16:14:41 PiW04x sddm[1526]: Setting default cursor
Apr 15 16:14:41 PiW04x sddm[1526]: Running display setup script "/usr/share/sddm/scripts/Xsetup"
Apr 15 16:14:41 PiW04x sddm[1526]: Display server started.
Apr 15 16:14:41 PiW04x sddm[1526]: Socket server starting...
Apr 15 16:14:41 PiW04x sddm[1526]: Socket server started.
Apr 15 16:14:41 PiW04x sddm[1526]: Loading theme configuration from "/usr/share/sddm/themes/breeze/theme.conf"
Apr 15 16:14:41 PiW04x sddm[1526]: Greeter starting...
Apr 15 16:14:41 PiW04x sddm[1526]: Adding cookie to "/var/run/sddm/{d02c7274-2c9f-452f-8967-bc8fcc638d42}"
Apr 15 16:14:41 PiW04x sddm-helper[21546]: [PAM] Starting...
Apr 15 16:14:41 PiW04x sddm-helper[21546]: [PAM] Authenticating...
Apr 15 16:14:41 PiW04x sddm-helper[21546]: [PAM] returning.
Apr 15 16:14:41 PiW04x sddm-helper[21546]: pam_unix(sddm-greeter:session): session opened for user sddm by (uid=0)
Apr 15 16:14:41 PiW04x systemd-logind[1344]: New session 6 of user sddm.
Apr 15 16:14:41 PiW04x systemd[1]: Started Session 6 of user sddm.
Apr 15 16:14:41 PiW04x sddm[1526]: Greeter session started successfully
Apr 15 16:14:41 PiW04x sddm-greeter[21549]: High-DPI autoscaling not Enabled
Apr 15 16:14:41 PiW04x sddm-greeter[21549]: Loading theme configuration from "/usr/share/sddm/themes/breeze/theme.conf"
Apr 15 16:14:41 PiW04x sddm-greeter[21549]: Reading from "/usr/share/xsessions/plasma.desktop"
Apr 15 16:14:41 PiW04x sddm-greeter[21549]: inotify_add_watch("/usr/share/wayland-sessions") failed: "No such file or directory"
Apr 15 16:14:41 PiW04x sddm-greeter[21549]: Connected to the daemon.
Apr 15 16:14:41 PiW04x sddm[1526]: Message received from greeter: Connect
Apr 15 16:14:41 PiW04x sddm-greeter[21549]: Loading file:///usr/share/sddm/themes/breeze/Main.qml...
Apr 15 16:14:41 PiW04x sddm-greeter[21549]: QObject: Cannot create children for a parent that is in a different thread.
(Parent is SDDM::GreeterApp(0x7ffd57674ac0), parent's thread is QThread(0x5633a05bd8c0), current thread is QThread(0x5633a0888440)
Apr 15 16:14:41 PiW04x sddm-greeter[21549]: QObject: Cannot create children for a parent that is in a different thread.
(Parent is SDDM::GreeterApp(0x7ffd57674ac0), parent's thread is QThread(0x5633a05bd8c0), current thread is QThread(0x5633a0888440)
Apr 15 16:14:41 PiW04x sddm-greeter[21549]: QObject: Cannot create children for a parent that is in a different thread.
(Parent is SDDM::GreeterApp(0x7ffd57674ac0), parent's thread is QThread(0x5633a05bd8c0), current thread is QThread(0x5633a0888440)
Apr 15 16:14:41 PiW04x sddm-greeter[21549]: QObject::installEventFilter(): Cannot filter events for objects in a different thread.
Apr 15 16:14:41 PiW04x sddm-greeter[21549]: QObject: Cannot create children for a parent that is in a different thread.
(Parent is SDDM::GreeterApp(0x7ffd57674ac0), parent's thread is QThread(0x5633a05bd8c0), current thread is QThread(0x5633a0888440)
Apr 15 16:14:41 PiW04x dbus-daemon[21557]: [session uid=119 pid=21555] AppArmor D-Bus mediation is enabled
Apr 15 16:14:41 PiW04x sddm-greeter[21549]: QObject: Cannot create children for a parent that is in a different thread.
(Parent is SDDM::GreeterApp(0x7ffd57674ac0), parent's thread is QThread(0x5633a05bd8c0), current thread is QThread(0x5633a0888440)
Apr 15 16:14:41 PiW04x sddm-greeter[21549]: QObject::installEventFilter(): Cannot filter events for objects in a different thread.
Apr 15 16:14:41 PiW04x sddm-greeter[21549]: Cannot watch QRC-like path ":/icons/hicolor/index.theme"
Apr 15 16:14:41 PiW04x sddm-greeter[21549]: Adding view for "VGA-1-1" QRect(0,0 1920x1080)
Apr 15 16:14:41 PiW04x sddm-greeter[21549]: Message received from daemon: Capabilities
Apr 15 16:14:41 PiW04x sddm-greeter[21549]: Message received from daemon: HostName
Apr 15 16:14:43 PiW04x systemd-logind[1344]: Removed session 1.
Apr 15 16:14:45 PiW04x acpid[1332]: client 21486[0:0] has disconnected
Apr 15 16:14:45 PiW04x acpid[1332]: client connected from 21486[0:0]
Apr 15 16:14:45 PiW04x acpid[1332]: 1 client rule loaded
Apr 15 16:14:47 PiW04x acpid[1332]: client 21486[0:0] has disconnected
Apr 15 16:14:51 PiW04x login[21372]: pam_unix(login:session): session opened for user const by LOGIN(uid=0)
Apr 15 16:14:51 PiW04x systemd-logind[1344]: New session 7 of user const.
Apr 15 16:14:51 PiW04x systemd[1]: Started Session 7 of user const.
Apr 15 16:15:32 PiW04x org.freedesktop.Notifications[1942]: org.kde.knotifications: WaitForName: Service was not registered within timeout
xorg.0.log：https://pastebin.com/1LJxhS5w
旧版本：https://pastebin.com/HpLLsrEE
.xsession 错误：https://pastebin.com/F55mzmXP
更新
设法使用 连接到 WiFi nmcli。
清除kubuntu-desktop kde-* *plasma*，然后安装，只plasma-desktop修复了这个问题，但缺少几个功能。安装后，kubuntu-desktop我又回到了之前的状态（没有条形图，没有背景）
答案1
通过清除所有 kde 和 plasma 包（参见更新）然后分批安装来修复此问题。设法将范围缩小到print-manager。
显然，打印机安装错误可能会导致等离子崩溃。