我升级到了 Ubuntu 15.04。重启后一切正常。我关闭了机器。
第二天早上，我重启了电脑，结果我的蓝牙键盘（Logitech diNovo，大约 6 年前的）无法使用。菜单栏中没有蓝牙图标，系统设置中的蓝牙选项卡完全变灰，蓝牙处于关闭状态，无法打开。
自 2009 年以来，我曾成功使用同一个键盘运行多个 Ubuntu 版本。
我搜索了一下，发现很多人有类似的问题。这可能与 bluez 从版本 4 升级到版本 5 有关？不确定。
检测到蓝牙设备：
[fjord:~] lsusb
Bus 004 Device 002: ID 8087:8000 Intel Corp.
Bus 004 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 003 Device 002: ID 8087:8008 Intel Corp.
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 002: ID 174c:3074 ASMedia Technology Inc. ASM1074 SuperSpeed hub
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 003: ID 1058:0704 Western Digital Technologies, Inc. My Passport Essential (WDME)
Bus 001 Device 002: ID 174c:2074 ASMedia Technology Inc. ASM1074 High-Speed hub
Bus 001 Device 019: ID 046d:c70c Logitech, Inc. BT Mini-Receiver (HID proxy mode)
Bus 001 Device 018: ID 046d:c70b Logitech, Inc. BT Mini-Receiver (HID proxy mode)
Bus 001 Device 017: ID 046d:0b02 Logitech, Inc. C-UV35 [Bluetooth Mini-Receiver] (HID proxy mode)
Bus 001 Device 005: ID 1bcf:0005 Sunplus Innovation Technology Inc.
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
单个接收器小部件负责该列表中的设备 019、018 和 017。（如果我拔下小部件，所有这三条设备线都会消失。）
但有些不对劲：
[fjord:~] sudo service bluetooth status
● bluetooth.service - Bluetooth service
Loaded: loaded (/lib/systemd/system/bluetooth.service; enabled; vendor preset: enabled)
Active: inactive (dead)
进而：
[fjord:~] sudo service bluetooth start
[fjord:~] sudo service bluetooth status
● bluetooth.service - Bluetooth service
Loaded: loaded (/lib/systemd/system/bluetooth.service; enabled; vendor preset: enabled)
Active: active (running) since Thu 2015-05-21 16:09:46 PDT; 13min ago
Main PID: 3709 (bluetoothd)
CGroup: /system.slice/bluetooth.service
└─3709 /usr/sbin/bluetoothd -n
May 21 16:09:46 fjord bluetoothd[3709]: bluetoothd[3709]: DIS cannot start: GATT is disabled
May 21 16:09:46 fjord bluetoothd[3709]: bluetoothd[3709]: Failed to init deviceinfo plugin
May 21 16:09:46 fjord bluetoothd[3709]: bluetoothd[3709]: Failed to init proximity plugin
May 21 16:09:46 fjord bluetoothd[3709]: bluetoothd[3709]: Failed to init time plugin
May 21 16:09:46 fjord bluetoothd[3709]: bluetoothd[3709]: Failed to init alert plugin
May 21 16:09:46 fjord bluetoothd[3709]: bluetoothd[3709]: Failed to init thermometer plugin
May 21 16:09:46 fjord bluetoothd[3709]: Failed to init gatt_example plugin
May 21 16:09:46 fjord bluetoothd[3709]: Bluetooth Management interface initialized
May 21 16:09:46 fjord bluetoothd[3709]: bluetoothd[3709]: Failed to init gatt_example plugin
May 21 16:09:46 fjord bluetoothd[3709]: bluetoothd[3709]: Bluetooth Management interface initialized
其他诊断：
[fjord:~] lsmod | grep bluetooth
bluetooth 491520 8 bnep,btusb
[fjord:~] uname -a
Linux fjord 3.19.0-18-generic #18-Ubuntu SMP Tue May 19 18:31:35 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
[fjord:~] dmesg | grep -i firmware
[ 0.201123] [Firmware Bug]: ACPI: BIOS _OSI(Linux) query ignored
[fjord:~] bluetoothd -v
4.101
有人知道如何解决这个问题吗？谢谢。
[更新]如果我移除 USB 加密狗并在按住红色按钮的同时重新插入它，我可以看到如下所示的内容：
[fjord:~] sudo service bluetooth status
● bluetooth.service - Bluetooth service
Loaded: loaded (/lib/systemd/system/bluetooth.service; enabled; vendor preset: enabled)
Active: active (running) since Sun 2015-05-24 03:11:26 PDT; 3min 50s ago
Main PID: 2162 (bluetoothd)
CGroup: /system.slice/bluetooth.service
└─2162 /usr/sbin/bluetoothd -n
May 24 03:12:47 fjord bluetoothd[2162]: Endpoint registered: sender=:1.44 path=/MediaEndpoint/BlueZ4/HFPAG
May 24 03:12:47 fjord bluetoothd[2162]: Endpoint registered: sender=:1.44 path=/MediaEndpoint/BlueZ4/HFPHS
May 24 03:12:47 fjord bluetoothd[2162]: Endpoint registered: sender=:1.44 path=/MediaEndpoint/BlueZ4/A2DPSource
May 24 03:12:47 fjord bluetoothd[2162]: Endpoint registered: sender=:1.44 path=/MediaEndpoint/BlueZ4/A2DPSink
May 24 03:12:47 fjord bluetoothd[2162]: bluetoothd[2162]: Endpoint registered: sender=:1.44 path=/MediaEndpoint/BlueZ4/HFPAG
May 24 03:12:47 fjord bluetoothd[2162]: bluetoothd[2162]: Endpoint registered: sender=:1.44 path=/MediaEndpoint/BlueZ4/HFPHS
May 24 03:12:47 fjord bluetoothd[2162]: bluetoothd[2162]: Endpoint registered: sender=:1.44 path=/MediaEndpoint/BlueZ4/A2DPSource
May 24 03:12:47 fjord bluetoothd[2162]: bluetoothd[2162]: Endpoint registered: sender=:1.44 path=/MediaEndpoint/BlueZ4/A2DPSink
May 24 03:12:47 fjord bluetoothd[2162]: Adapter /org/bluez/2162/hci0 has been enabled
May 24 03:12:47 fjord bluetoothd[2162]: bluetoothd[2162]: Adapter /org/bluez/2162/hci0 has been enabled
看起来更健康，但键盘仍然无法工作。
答案1
原来只是电池没电了！电池肯定是在升级后没电了，所以我错误地把责任归咎于升级。时机不对。抱歉发出了噪音。