How to enable Atheros AR242x / AR542x Wireless Network Adapter on CentOS 7

The Linux kernel version 3.10 used by CentOS 7 does not come with a driver for Atheros AR242x / AR542x Wireless Network Adapter. When my Lenovo X200 laptop boots into CentOS 7, the WiFi light turns off. Though the WiFi light was blinking as it boots into Windows 8.

Issue a lshw command to check the hardware:
# lshw -C network

It shows
*-network UNCLAIMED
description: Ethernet controller
product: AR242x / AR542x Wireless Network Adapter (PCI-Express)
vendor: Qualcomm Atheros
physical id: 0
bus info: pci@0000:03:00.0
version: 01
width: 64 bits
clock: 33MHz
capabilities: pm msi pciexpress msix bus_master cap_list
configuration: latency=0
resources: memory:f2500000-f250ffff

Which means no proper driver for the Atheros wireless network adapter is loaded.

Issue a modprobe command to load kernel module driver ath5k,
# modprobe -v ath5k

It shows
modprobe: FATAL: Module ath5k not found.
How to enable Atheros AR242x / AR542x Wireless Network Adapter on CentOS 7 continued »

Martin Fowler 對 NoSQL 資料庫的分類

Martin Fowler 對 NoSQL 資料庫的分類:
Key-Value Pair: Memcached, Coherence, Redis
Tabular: BigTable, HBase, Accumulo
Document-oriented: MongoDB, CouchDB, Cloudant

NoSQL Database Comparison

A very good NoSQL database comparison can be found at Cassandra vs MongoDB vs CouchDB vs Redis vs Riak vs HBase vs Couchbase vs Neo4j vs Hypertable vs ElasticSearch vs Accumulo vs VoltDB vs Scalaris comparison.
Keep it as a reference.

OpenStack Installation Using devstack

First, install Ubuntu 14.04 server and create an account named stack and add a line in /etc/sudoers as follows:

so that user stack can issue sudo without password.
OpenStack Installation Using devstack continued »

Keep My Accounts from Hack by Using Random Passwords

用慣了 Ubuntu 之後也就習慣了 sudo, 於是不再登入 root 也不再登入許多帳號。 但是某些用來安裝網站的帳號為了軟體升級, 偶爾還是得以 ftp 登入,於是就故意為這些帳號設定一長串連自己都不記得的密碼, 等到要做軟體升級時, 再以 sudo passwd 把這些帳號的密碼改短一點, 等升級完畢又再把密碼弄亂。
網路上有一些隨機產生長串密碼的方法, 例如 10 Ways to Generate a Random Password from the Command Line, 其中我最喜歡的是 date | md5sum -openssl rand -base64 32, 簡單又有效。

Pronunciation of some symbols

^ caret 插入符號
~ tilde 波浪 Pronunciation of some symbols continued »

SQL Server 無法安裝資料庫圖表支援物件

SQL Server 2008 以 Windows 驗證方式登入,建立資料庫之後無法建立資料庫圖表,此時必須執行下列指令將資料庫歸給一個有效的帳號,例如sa:
SQL SERVER – ERROR: FIX – Database diagram support objects cannot be installed because this database does not have a valid owner

LVM: steps after disk replacement

After /dev/sdb crashes, I replace a new disk and restore the partition table by issuing:
# sfdisk -d /dev/sda | sfdisk --force /dev/sdb
Then the lvm reports Couldn't find device with uuid p79BEJ-smM3-gxzB-tuEf-pU5N-7HEm-7BOLfP.
To remove the lost PV:
# vgreduce --removemissing --force vg_osc1
where vg_osc1 is the name of VG.
LVM: steps after disk replacement continued »

先安裝 Scientific Linux Minimum Installation 再安裝 Desktop Environment

安裝 Scientific Linux 時使用 Boot CD,所有的安裝套件都從網路上抓,網址:
為了節省時間,選擇 Minimum Installation。
安裝完畢之後,再安裝 Desktop Environment,作法參考
先安裝 Scientific Linux Minimum Installation 再安裝 Desktop Environment continued »


T 客邦 的文章:靠一支隨身碟,Ubuntu系統、檔案、設定全包
這個方法真不錯,只用一支 4GB USB 隨身碟就可以使用 Linux。