我在安装有 Ubuntu 14.04 LTS 的新电脑上修复无线网络速度慢得无法使用的问题。过了一会儿，我就没有网络连接了。如果我重新启动电脑，网络连接就会恢复（速度仍然很慢），但连接通常会变得更慢，之后我就无法使用它了。
我使用的无线网卡是 D-Link DWA-548 pci-express。
我在谷歌搜索中遇到了几个类似的问题，但没有任何建议能帮助我。
以下是一些有用的命令，它们可以打印出有用的信息。我看到一些大师要求提供这些信息（从 varunendra 的一篇帖子中得到）：
代码：
====================================================================================
lsb_release -d
--------------
Description: Ubuntu 14.04.2 LTS
====================================================================================
uname -mr
---------
3.13.0-55-generic x86_64
====================================================================================
lspci -nnk | grep -iA2 net
--------------------------
02:00.0 Ethernet controller [0200]: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller [10ec:8168] (rev 0c)
Subsystem: Gigabyte Technology Co., Ltd Motherboard [1458:e000]
Kernel driver in use: r8169
03:00.0 Network controller [0280]: Ralink corp. RT5392 PCIe Wireless Network Adapter [1814:5392]
Subsystem: D-Link System Inc Device [1186:3c06]
Kernel driver in use: rt2800pci
====================================================================================
lsmod
-----
Module Size Used by
...
rt2800pci 13598 0
rt2800mmio 20986 1 rt2800pci
rt2800lib 88867 2 rt2800pci,rt2800mmio
rt2x00pci 13287 1 rt2800pci
rt2x00mmio 13603 2 rt2800pci,rt2800mmio
rt2x00lib 55250 5 rt2x00pci,rt2800lib,rt2800pci,rt2800mmio,rt2x00mmio
mac80211 639514 3 rt2x00lib,rt2x00pci,rt2800lib
cfg80211 541326 2 mac80211,rt2x00lib
r8169 67581 0
...
====================================================================================
iwconfig
--------
eth0 no wireless extensions.
lo no wireless extensions.
wlan0 IEEE 802.11bgn ESSID:"xx xxx"
Mode:Managed Frequency:2.412 GHz Access Point: <masked_address>
Bit Rate=27 Mb/s Tx-Power=20 dBm
Retry short limit:7 RTS thr:off Fragment thr:off
Power Management:off
Link Quality=47/70 Signal level=-63 dBm
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:37 Invalid misc:125 Missed beacon:0
====================================================================================
rfkill list all
---------------
0: phy0: Wireless LAN
Soft blocked: no
Hard blocked: no
====================================================================================
iw reg get
----------
country 00:
(2402 - 2472 @ 40), (3, 20)
(2457 - 2482 @ 40), (3, 20), PASSIVE-SCAN, NO-IBSS
(2474 - 2494 @ 20), (3, 20), NO-OFDM, PASSIVE-SCAN, NO-IBSS
(5170 - 5250 @ 40), (3, 20), PASSIVE-SCAN, NO-IBSS
(5735 - 5835 @ 40), (3, 20), PASSIVE-SCAN, NO-IBSS
====================================================================================
nm-tool
-------
NetworkManager Tool
State: connected (global)
- Device: wlan0 [Ex Mente]
Type: 802.11 WiFi
Driver: rt2800pci
State: connected
Default: yes
HW Address: <masked_address>
Capabilities:
Speed: 14 Mb/s
Wireless Properties
WEP Encryption: yes
WPA Encryption: yes
WPA2 Encryption: yes
Wireless Access Points (* = current AP)
*Ex Mente: Infra, <masked_address>, Freq 2412 MHz, Rate 54 Mb/s, Strength 57 WPA2
IPv4 Settings:
.
.
.
- Device: eth0
Type: Wired
Driver: r8169
State: unavailable
Default: no
HW Address: <masked_address>
Capabilities:
Carrier Detect: yes
Wired Properties
Carrier: off
====================================================================================
sudo iwlist scan
----------------
eth0 Interface doesn't support scanning.
lo Interface doesn't support scanning.
wlan0 Scan completed :
Cell 01 - Address: <masked_address>
Channel:1
Frequency:2.412 GHz (Channel 1)
Quality=53/70 Signal level=-57 dBm
Encryption key:on
ESSID:"Ex Mente"
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 18 Mb/s
24 Mb/s; 36 Mb/s; 54 Mb/s
Bit Rates:6 Mb/s; 9 Mb/s; 12 Mb/s; 48 Mb/s
Mode:Master
Extra:tsf=0000000000000000
Extra: Last beacon: 56ms ago
IE: Unknown: 00084578204D656E7465
IE: Unknown: 010882848B962430486C
IE: Unknown: 030101
IE: Unknown: 2A0104
IE: Unknown: 2F0104
IE: IEEE 802.11i/WPA2 Version 1
Group Cipher : CCMP
Pairwise Ciphers (1) : CCMP
Authentication Suites (1) : PSK
IE: Unknown: 32040C121860
IE: Unknown: 2D1AFE181BFFFF000001000000000000000000000000000000000000
IE: Unknown: 3D1601051700000000000000000000000000000000000000
IE: Unknown: DD7D0050F204104A00011010440001021041000100103B00010310470010550364D39CAC0C7C62E4DD6D11DFF2AD102100074E6574676561721023000944474E3232303076331024000944474E32323030763310420004313233341054000800060050F20400011011000944474E323230307633100800020084103C000101
IE: Unknown: DD090010180205F02C0000
IE: Unknown: DD180050F2020101800003A4000027A4000042435E0062322F00
====================================================================================
egrep '^(#.*device|[^#]|$)' /etc/udev/rules.d/70-persistent-net.rules
---------------------------------------------------------------------
# PCI device 0x10ec:0x8168 (r8169)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="<masked_address>", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0"
# PCI device 0x1814:0x5392 (rt2800pci)
SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="<masked_address>", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="wlan*", NAME="wlan0"
====================================================================================
dmesg | grep 'wlan|rt2'
-----------------------
我也尝试设置 nohwcrypt，但没有成功：
代码：
sudo modprobe -rv rt2800pci
sudo modprobe -v rt2800pci nohwcrypt=Y
导致我的无线无法连接。