为什么light-locker解锁后一直黑屏？

Question

在使用 Light-Locker 锁定我的屏幕后，带有新创建的用户的 Xubuntu 16.04 完全修补机器不会让我解锁（无论锁定是手动激活还是通过超时激活）。该屏幕保持黑色（但供电）上正确输入密码

从 tty1 杀死 light-locker 将显示桌面（从而防止进一步锁定）。

尝试的步骤：

• 在灯箱设置和电源设置中启用/禁用锁定（无变化）
• 使用 xscreensaver 而不是 Light-Locker（有效）
• 测试问题是否与暂停或关闭盖子有关（不是）
  • 但是，在挂起黑屏后会显示This session is locked: You will be redirected to the unlock dialog automatically in a few seconds消息 - 没有发生任何重定向
• 清除+重新安装 lightdm、light-locker 和 xubuntu-default-settings
• 使用loginctl unlock-session没有效果
• systemctl status lightdm 只显示（无害的，预期的）关于 kwallet pam 模块丢失的消息
• 检查 dpkg 日志是否在“它有效”和“它不再起作用”之间进行升级（无可疑）并启动以前的内核（问题仍然存在）
• 会话启动的 Light-Locker 和手动启动的 Light-Locker 之间的行为比较（没有区别）
• 将用户添加到组nopasswdlogin组（锁定后立即出现黑屏，而不是输入密码后）

在弄清楚如何解决这个问题时，哪些额外的步骤可以证明是有用的？

调试日志：

$ export LC_ALL=C; light-locker --debug & ( sleep 5; echo "## Locking now"; light-locker-command --lock; sleep 10; echo "### 10 seconds have passed - entering password now"; sleep 10; echo "### 10 more seconds have passwd - Killing"; killall light-locker; sleep 5; echo "### Killed now" )  
[1] 23463
[gs_debug_init] gs-debug.c:106 (00:08:32):   Debugging enabled
[main] light-locker.c:142 (00:08:32):    initializing light-locker 1.7.0
[main] light-locker.c:144 (00:08:32):    lock after screensaver 10
[main] light-locker.c:145 (00:08:32):    late locking 0
[main] light-locker.c:146 (00:08:32):    lock on suspend 1
[main] light-locker.c:147 (00:08:32):    lock on lid 0
[main] light-locker.c:148 (00:08:32):    idle hint 1
[query_session_id] gs-listener-dbus.c:2088 (00:08:32):   org.freedesktop.login1.NoSessionForPID raised:
 PID 23463 does not belong to any known session


[init_session_id] gs-listener-dbus.c:2180 (00:08:32):    Got session-id: (null)
[query_sd_session_id] gs-listener-dbus.c:2164 (00:08:32):    Couldn't determine our own sd session id: No such process
[init_session_id] gs-listener-dbus.c:2185 (00:08:32):    Got sd-session-id: (null)
[init_seat_path] gs-listener-dbus.c:2262 (00:08:32):     Got seat: /org/freedesktop/DisplayManager/Seat0
[gs_listener_delay_suspend] gs-listener-dbus.c:449 (00:08:32):   Delay suspend
[gs_listener_x11_acquire] gs-listener-x11.c:172 (00:08:32):  ScreenSaver Registered
[listener_dbus_handle_system_message] gs-listener-dbus.c:1330 (00:08:32):    obj_path=/org/freedesktop/DBus interface=org.freedesktop.DBus method=NameAcquired destination=:1.316
## Locking now
[gs_grab_grab_root] gs-grab-x11.c:647 (00:08:37):    Grabbing the root window
[gs_grab_get_keyboard] gs-grab-x11.c:153 (00:08:37):     Grabbing keyboard widget=E3
[gs_grab_get_mouse] gs-grab-x11.c:213 (00:08:37):    Grabbing mouse widget=E3
[gs_manager_create_windows_for_screen] gs-manager.c:548 (00:08:37):  Creating 1 windows for screen 0
[gs_manager_create_window_for_monitor] gs-manager.c:324 (00:08:37):  Creating window for monitor 0 [0,0] (1600x900)
[update_geometry] gs-window-x11.c:197 (00:08:37):    got geometry for monitor 0: x=0 y=0 w=1600 h=900
[update_geometry] gs-window-x11.c:210 (00:08:37):    using geometry for monitor 0: x=0 y=0 w=1600 h=900
[update_geometry] gs-window-x11.c:197 (00:08:37):    got geometry for monitor 0: x=0 y=0 w=1600 h=900
[update_geometry] gs-window-x11.c:210 (00:08:37):    using geometry for monitor 0: x=0 y=0 w=1600 h=900
[gs_window_move_resize_window] gs-window-x11.c:243 (00:08:37):   Move and/or resize window on monitor 0: x=0 y=0 w=1600 h=900
[update_geometry] gs-window-x11.c:197 (00:08:37):    got geometry for monitor 0: x=0 y=0 w=1600 h=900
[update_geometry] gs-window-x11.c:210 (00:08:37):    using geometry for monitor 0: x=0 y=0 w=1600 h=900
[gs_window_move_resize_window] gs-window-x11.c:243 (00:08:37):   Move and/or resize window on monitor 0: x=0 y=0 w=1600 h=900
[update_geometry] gs-window-x11.c:197 (00:08:37):    got geometry for monitor 0: x=0 y=0 w=1600 h=900
[update_geometry] gs-window-x11.c:210 (00:08:37):    using geometry for monitor 0: x=0 y=0 w=1600 h=900
[gs_window_move_resize_window] gs-window-x11.c:243 (00:08:37):   Move and/or resize window on monitor 0: x=0 y=0 w=1600 h=900
[gs_manager_timed_switch] gs-manager.c:445 (00:08:37):   Start switch to greeter timer
[gs_window_xevent] gs-window-x11.c:369 (00:08:37):   not raising our windows
[window_map_event_cb] gs-manager.c:233 (00:08:37):   Handling window map_event event
[gs_listener_resume_suspend] gs-listener-dbus.c:513 (00:08:37):  Resume suspend: fd=14
[manager_maybe_grab_window] gs-manager.c:204 (00:08:37):     Moving grab to 0x5595f8d5a290
[gs_grab_move_keyboard] gs-grab-x11.c:450 (00:08:37):    Moving keyboard grab from E3 to 3A0000C
[gs_grab_move_keyboard] gs-grab-x11.c:457 (00:08:37):    *** doing X server grab
[gs_grab_release_keyboard] gs-grab-x11.c:279 (00:08:37):     Ungrabbing keyboard
[gs_grab_get_keyboard] gs-grab-x11.c:153 (00:08:37):     Grabbing keyboard widget=3A0000C
[gs_grab_move_keyboard] gs-grab-x11.c:479 (00:08:37):    *** releasing X server grab
[gs_grab_move_mouse] gs-grab-x11.c:395 (00:08:37):   Moving pointer grab from E3 to 3A0000C
[gs_grab_move_mouse] gs-grab-x11.c:402 (00:08:37):   *** doing X server grab
[gs_grab_release_mouse] gs-grab-x11.c:320 (00:08:37):    Ungrabbing pointer
[gs_grab_get_mouse] gs-grab-x11.c:213 (00:08:37):    Grabbing mouse widget=3A0000C
[gs_grab_move_mouse] gs-grab-x11.c:425 (00:08:37):   *** releasing X server grab
[listener_dbus_handle_system_message] gs-listener-dbus.c:1330 (00:08:37):    obj_path=/org/freedesktop/login1 interface=org.freedesktop.DBus.Properties method=PropertiesChanged destination=(null)
[update_geometry] gs-window-x11.c:197 (00:08:37):    got geometry for monitor 0: x=0 y=0 w=1600 h=900
[update_geometry] gs-window-x11.c:210 (00:08:37):    using geometry for monitor 0: x=0 y=0 w=1600 h=900
[gs_window_move_resize_window] gs-window-x11.c:243 (00:08:37):   Move and/or resize window on monitor 0: x=0 y=0 w=1600 h=900
[update_geometry] gs-window-x11.c:197 (00:08:37):    got geometry for monitor 0: x=0 y=0 w=1600 h=900
[update_geometry] gs-window-x11.c:210 (00:08:37):    using geometry for monitor 0: x=0 y=0 w=1600 h=900
[gs_window_move_resize_window] gs-window-x11.c:243 (00:08:37):   Move and/or resize window on monitor 0: x=0 y=0 w=1600 h=900
[gs_listener_send_lock_session] gs-listener-dbus.c:180 (00:08:38):   Send lock session
[listener_dbus_handle_system_message] gs-listener-dbus.c:1330 (00:08:38):    obj_path=(null) interface=(null) method=(null) destination=:1.316
[listener_dbus_handle_system_message] gs-listener-dbus.c:1330 (00:08:39):    obj_path=/org/freedesktop/login1/session/c5 interface=org.freedesktop.DBus.Properties method=PropertiesChanged destination=(null)
[listener_dbus_handle_system_message] gs-listener-dbus.c:1330 (00:08:39):    obj_path=/org/freedesktop/login1/session/c12 interface=org.freedesktop.DBus.Properties method=PropertiesChanged destination=(null)
[listener_dbus_handle_system_message] gs-listener-dbus.c:1330 (00:08:39):    obj_path=/org/freedesktop/login1/seat/seat0 interface=org.freedesktop.DBus.Properties method=PropertiesChanged destination=(null)
process 23463: arguments to dbus_message_new_method_call() were incorrect, assertion "path != NULL" failed in file ../../dbus/dbus-message.c line 1340.
This is normally a bug in some application using the D-Bus library.
[query_session_active] gs-listener-dbus.c:1124 (00:08:39):   Couldn't allocate the dbus message
[listener_dbus_handle_system_message] gs-listener-dbus.c:1361 (00:08:39):    systemd notified ActiveSession 0
[listener_session_switched_cb] gs-monitor.c:298 (00:08:39):  Session switched: 0
[gs_manager_stop_switch] gs-manager.c:456 (00:08:39):    Stop switch to greeter timer
[listener_dbus_handle_system_message] gs-listener-dbus.c:1330 (00:08:39):    obj_path=/org/freedesktop/login1/seat/seat0 interface=org.freedesktop.DBus.Properties method=PropertiesChanged destination=(null)
[listener_dbus_handle_system_message] gs-listener-dbus.c:1330 (00:08:39):    obj_path=/org/freedesktop/login1/session/c12 interface=org.freedesktop.DBus.Properties method=PropertiesChanged destination=(null)
[listener_dbus_handle_system_message] gs-listener-dbus.c:1330 (00:08:39):    obj_path=/org/freedesktop/login1/user/_108 interface=org.freedesktop.DBus.Properties method=PropertiesChanged destination=(null)
[listener_dbus_handle_system_message] gs-listener-dbus.c:1330 (00:08:39):    obj_path=/org/freedesktop/login1/seat/seat0 interface=org.freedesktop.DBus.Properties method=PropertiesChanged destination=(null)
process 23463: arguments to dbus_message_new_method_call() were incorrect, assertion "path != NULL" failed in file ../../dbus/dbus-message.c line 1340.
This is normally a bug in some application using the D-Bus library.
[query_session_active] gs-listener-dbus.c:1124 (00:08:39):   Couldn't allocate the dbus message
[listener_dbus_handle_system_message] gs-listener-dbus.c:1361 (00:08:39):    systemd notified ActiveSession 0
[listener_session_switched_cb] gs-monitor.c:298 (00:08:39):  Session switched: 0
[listener_dbus_handle_system_message] gs-listener-dbus.c:1330 (00:08:39):    obj_path=/org/freedesktop/login1/session/c5 interface=org.freedesktop.login1.Session method=Lock destination=(null)
### 10 seconds have passed - entering password now
[listener_dbus_handle_system_message] gs-listener-dbus.c:1330 (00:08:51):    obj_path=/org/freedesktop/login1/session/c5 interface=org.freedesktop.login1.Session method=Unlock destination=(null)
[listener_dbus_handle_system_message] gs-listener-dbus.c:1330 (00:08:51):    obj_path=/org/freedesktop/login1/session/c13 interface=org.freedesktop.DBus.Properties method=PropertiesChanged destination=(null)
[listener_dbus_handle_system_message] gs-listener-dbus.c:1330 (00:08:51):    obj_path=/org/freedesktop/login1/session/c5 interface=org.freedesktop.DBus.Properties method=PropertiesChanged destination=(null)
[listener_dbus_handle_system_message] gs-listener-dbus.c:1330 (00:08:51):    obj_path=/org/freedesktop/login1/seat/seat0 interface=org.freedesktop.DBus.Properties method=PropertiesChanged destination=(null)
process 23463: arguments to dbus_message_new_method_call() were incorrect, assertion "path != NULL" failed in file ../../dbus/dbus-message.c line 1340.
This is normally a bug in some application using the D-Bus library.
[query_session_active] gs-listener-dbus.c:1124 (00:08:51):   Couldn't allocate the dbus message
[listener_dbus_handle_system_message] gs-listener-dbus.c:1361 (00:08:51):    systemd notified ActiveSession 0
[listener_session_switched_cb] gs-monitor.c:298 (00:08:51):  Session switched: 0
[xroot_filter] gs-listener-x11.c:124 (00:08:52):     ScreenSaver stopped
### 10 more seconds have passwd - Killing
### Killed now

将此与已知良好的系统进行比较可得出：

$ comm -3 <(grep -iv grab good | sed 's/[0-9:]\+/[NN]/g;s/[ \t]\+/ /g' | sort) <(grep -iv grab bad | sed 's/[0-9:]\+/[NN]/g;s/[ \t]\+/ /g' | sort) | head -n2
[init_session_id] gs-listener-dbus.c[NN] ([NN])[NN] Got session-id[NN] (null)
[init_session_id] gs-listener-dbus.c[NN] ([NN])[NN] Got session-id[NN] /org/freedesktop/login[NN]/session/c[NN]

事实上，会话设置似乎非常尴尬：

$ loginctl session-status
Could not get properties: No such process

Answer 1

TL;DR：如果 systemd 无法读取 /proc，light-locker 会使屏幕保持黑色

• light-locker取决于dbus提供IPC.
• dbus取决于systemd-logind提供session信息。
• systemd-logind取决于/proc提供process信息。

这意味着这不会很好地协同工作：

$ file /sbin/init
/sbin/init: symbolic link to /lib/systemd/systemd
$ mount | grep proc
proc on /proc type proc (rw,nosuid,nodev,noexec,relatime,hidepid=2,gid=1337)

并且不能期望：

hidepid 与 systemd 并不真正兼容。对不起。[..] 无论如何，关闭，因为这不是由 systemd 引起的。——伦纳特·波特林

部分解决方案 1

部分解决方案，因为它带有信息披露。

允许非特权程序（例如 systemd，在删除特权后）访问/proc.

$ sudo mount -o remount,hidepid=0 /proc
 # and fix /etc/fstab accordingly

部分解决方案2

部分解决方案，因为 systemd 可能会在其他地方崩溃，而不仅仅是 logind。

将 systemd-logind 添加到适当的组，通过添加服务 Drop-In 最方便地实现。

$ addgroup showpid
$ adduser myuser showpid
$ sudo mount -o remount,hidepid=2,gid=showpid /proc
 # and fix /etc/fstab accordingly
$ echo -e '[Service]\nSupplementaryGroups=showpid' | sudo tee /etc/systemd/system/systemd-logind.service.d/10-showpid.conf
$ sudo systemctl daemon-reload
$ sudo systemctl restart systemd-logind

在任一解决方案之后，Got session-id: (null)消息应该看起来更像Got session-id: /org/freedesktop/login1/c7并且 light-locker 将能够通过dbus.

我应该怎么做才能更快地解决这个问题？

• 如果某些事情发生了变化，而您无法快速弄清楚发生了什么变化，只需获取备份和diff -ruiN整个系统即可。
• 更准确地记录问题第一次发生的时间，因此按时间对日志文件/IDS 报告进行排序将很快揭示相关原因。
• 提交更多错误报告。应用程序在稍后会导致头痛和/或系统锁定的情况下静默失败是不可接受的。