Live Long and Prosper

在PosgreSQL有connection的情況下，刪除database或更名database

2013-07-03T22:31:00.001-07:00

 
SELECT pg_terminate_backend(procpid) FROM pg_stat_activity WHERE datname='<db_name>';DROP DATABASE <db_name>;
SELECT pg_terminate_backend(procpid) FROM pg_stat_activity WHERE datname='<db_name>';ALTER DATABASE <old_db_name> RENAME TO <new_db_name>;

SVN刪除所有missing的檔案

2013-07-03T18:07:00.003-07:00

svn st | grep ^! | awk '{print " --force "$2}' | xargs svn rm

Put Spring's applicationContext.xml into src/main/resources folder

2013-03-17T23:51:00.002-07:00

The standard folder layout of Maven is quite convenient for me, the applicationContext.xml is put into /webapp/WEB-INF instead of /src/main/resources folder. It conflicts the convention of Maven, therefore I add the following command in web.xml in order to load applicationContext.xml from /webapp/WEB-INF folder.


    contextConfigLocation
    classpath:applicationContext.xml

Reference: stackoverflow

安裝VIM的supertab plugin

2013-02-20T18:26:00.000-08:00

從 SuperTab 網頁下載最新的 supertab.vmb

vim supertab.vmb

# source 這個檔案
:so %

之後在 vim 中，只要用 tab 鍵，就可以做 auto completion

Ubuntu中使用SVN出現"Password for 'default' GNOME keyring"

2013-01-23T23:14:00.004-08:00

編輯~/.subversion/config，在[Auth]的裡面加入

password-stores =

Reference: ubuntu forum

升級到OSX 10.8 (Mountain Lion)後，pip使用遇到問題

2013-01-03T22:34:00.000-08:00

升級之後，使用pip安裝套件，卻出現下面這種狀況。

Traceback (most recent call last):
  File "/usr/local/bin/pip", line 5, in 
    from pkg_resources import load_entry_point
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 2603, in 
    working_set.require(__requires__)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 666, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 565, in resolve
    raise DistributionNotFound(req)  # XXX put more info here
pkg_resources.DistributionNotFound: pip==1.1

這時候要做的事情很容易，只需要把pip做升級，就可以解決這個問題。

sudo easy_install -U pip

Reference: stackoverflow

活用fping監控大量機器的狀態

2012-12-21T01:32:00.001-08:00

由於需要管理手中機器的存活狀態，找到了fping這個方便的指令來做這件事情，把需要監控的機器IP寫在一份.txt檔案中，格式如下：

100.65.206.219
100.65.206.220
100.65.206.221
100.65.206.222
100.65.206.223

接著執行這行指令，我在後面加上了

grep unreachable

是因為我只需要知道掛掉的機器是哪些，其中 -r 這個參數是retry的次數， -t 是timeout的長度(in millisec)。

# -r: retry count
# -t: timeout interval (in millisec)
sudo fping -f ip.txt -r 2 -t 50 | grep unreachable

當然，fping不只如此，他還可以指定要掃描的起始IP跟結束IP，或者是指定子網路遮罩。

fping -g 100.65.206.219 100.65.206.223
fping -g 100.65.206.0/24

開機時mount Samba drive

2012-12-19T01:30:00.003-08:00

修改/etc/fstab，加入下面的描述，其中_netdev是非常重要的設定，它會等到網路功能開啟之後，才將這個Samba drive mount上去

//${SAMBA_IP}/${SAMBA_FOLDER}  ${PATH_TO_MNT}    cifs    guest,_netdev   0 0

用watch的方式檢查process的存活狀況

2012-12-18T00:21:00.003-08:00

while true
do
    clear
    ps ax | grep -v grep | grep -v $0 | grep tomcat
    sleep 5
done

重複執行shell command

2012-11-28T08:24:00.000-08:00

最近在用bonnie++測試file system的benchmark，等待時間長而且同一個條件要測試許多次，在電腦前面等實在不好，找了重複執行shell command的指令。

首先，修改~/.bashrc

vim ~/.bashrc

加入：

repeat() {
    n=$1
    shift
    while [ $(( n -= 1 )) -ge 0 ]
    do
        "$@"
    done
}

讀bash環境設定

source ~/.bashrc

如此一來就可以重複執行shell command了！下列指令會重複執行3次

repeat 3  bonnie++ -u root -d /dev/hda

Reference: Always Right

砍掉Postgresql的connection

2012-10-03T02:46:00.000-07:00

在drop database的時候，既有的connection會阻止資料庫刪除的動作，這時候執行

SELECT procpid, (SELECT pg_terminate_backend(procpid)) as killed from pg_stat_activity
    WHERE current_query LIKE '<IDLE>';

Reference: stackoverflow

Windows命令列執行concurrent background processes的作法

2012-09-27T05:22:00.000-07:00

在Linux的command line中，如果要送出多個background processes，會在後面加上"&"符號，把他送入背景執行

sh foo.sh &
sh bar.sh &

在Windows則要用不同的方式去作這件事情，筆記一下

start foo.bat | start bar.bat

Reference: superuser

當RMI呼叫試圖存取127.0.0.1的時候

2012-09-17T06:12:00.000-07:00

錯誤訊息可能長這樣

Caused by: java.rmi.ConnectException: Connection refused to host: 127.0.0.1; nested exception is: java.net.ConnectException: Connection refused at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEnd point.java:574) at sun.rmi.transport.tcp.TCPChannel.createConnection( TCPChannel.java:185) at sun.rmi.transport.tcp.TCPChannel.newConnection(TCP Channel.java:171) at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:9 4) at org.springframework.remoting.rmi.RmiInvocationWrap per_Stub.invoke(Unknown Source) at org.springframework.remoting.rmi.RmiClientIntercep tor.doInvoke(RmiClientInterceptor.java:400) at org.springframework.remoting.rmi.RmiClientIntercep tor.doInvoke(RmiClientInterceptor.java:344) at org.springframework.remoting.rmi.RmiClientIntercep tor.invoke(RmiClientInterceptor.java:259) at org.springframework.aop.framework.ReflectiveMethod Invocation.proceed(ReflectiveMethodInvocation.java :185) at org.springframework.aop.framework.JdkDynamicAopPro xy.invoke(JdkDynamicAopProxy.java:209) at $Proxy0.settle(Unknown Source)

這個時候，通常是RMI server的/etc/hosts設定了localhost為127.0.0.1，
只要修改/etc/hosts，把localhost的entry改為真實IP，就可以正常運作了。

Reference: gflei.iteye.com

Ubuntu 12.04安裝DavMail並且收信

2012-09-03T00:26:00.000-07:00

把作業系統從Windows 7變成Ubuntu 12.04，有一些地方需要作調整，首當其衝的應該就是從Outlook改為Thunderbird，由於無法直接收Exchange server的mail，同事推薦了DavMail當作Thunderbird的agent收信，安裝跟設定上沒有遭遇到太多問題，只是DavMail在執行的時候，systray上看不到DavMail的圖示，如果要修改DavMail的設定就頭大了，所幸只要下面這一行command就可以讓這個圖示出現在systray上。

gsettings set com.canonical.Unity.Panel systray-whitelist "['all']"

另外記得要把DavMail進階設定中Exchange Protocol從Auto換成EWS，才可以正常收信哦。
Reference: davmail

觀察PostgreSQL的connection activity

2012-08-19T23:30:00.003-07:00

因為懷疑正在實作的應用程式在運作過程中有connection沒有關閉，找了下面這個方法去觀察PostgreSQL目前正在連線的connection，以及他們正在做什麼事情。

SELECT * FROM pg_stat_activity;

由於欄位太多，畫面變得很難閱讀，改成只拿必要的欄位：

SELECT datid, datname, current_query FROM pg_stat_activity;

 datid | datname| current_query
-------+--------+------------------------------------------------------------
 17075 | foobar | <IDLE>
 17075 | foobar | <IDLE>
 17075 | foobar | <IDLE>
 17075 | foobar | <IDLE> in transaction
 17075 | foobar | update public..., sele...
 17075 | foobar | <IDLE> in transaction
 17075 | foobar | SELECT datid, datname, current_query FROM pg_stat_activity;
(7 rows)

其中有幾個連線時間長到有點誇張，加入age()函式檢查這幾個connection的存續時間：

SELECT datid,datname,current_query,age(now(),query_start) as age
    FROM pg_stat_activity ORDER BY age DESC;

 datid | datname| current_query                                              |  age
-------+--------+------------------------------------------------------------+-------
 17075 | foobar | <IDLE> in transaction                                      |2 days 19:59:37.157806
 17075 | foobar | update public..., sele...                                  |2 days 19:59:37.067323
 17075 | foobar | <IDLE>                                                     |00:49:42.900198
 17075 | foobar | <IDLE>                                                     |00:49:42.899244
 17075 | foobar | <IDLE>                                                     |00:49:42.606484
 17075 | foobar | <IDLE>                                                     |00:17:38.719693
 17075 | foobar | SELECT datid, datname, current_query FROM pg_stat_activity;|00:00:00
(7 rows)

Reference: chrismils

修改PostgreSQL使用者的密碼

2012-08-16T23:14:00.002-07:00

下面例子是把使用者'foo'的密碼改為'bar'.

ALTER USER foo WITH PASSWORD 'bar';

Reference: PostgreSQL

不輸入帳號密碼，掛載Shaba share drive

2012-07-31T22:44:00.002-07:00

mount -t cifs //${SAMBA_SERVER}/${SHARE_FOLDER} ${MOUNT_POINT} -o guest

檢查Process有沒有正常running

2012-07-31T00:09:00.002-07:00

if [ -z "$(pgrep -f ${SERVICE})" ] 
  then
    echo Not Running
  else 
    echo Running
fi

加入ssh login速度

2012-07-26T01:33:00.001-07:00

只要把UseDNS關掉，登入速度就可以馬上變快！

sed -i 's/#UseDNS yes/UseDNS no/g' /etc/ssh/sshd_config
service sshd restart

Reference: UNIX&LINUX

使用bash script修改使用者的密碼

2012-07-24T23:18:00.003-07:00

sudo useradd test
sudo echo "password" | passwd test --stdin

Reference: stackoverflow

[Solved] CentOS 5.5做yum install ant遇到Missing Dependency: /usr/bin/rebuild-security-providers is needed by package java-1.4.2-gcj-compat-1.4.2.0-40jpp.115.x86_64

2012-07-08T02:10:00.000-07:00

做yum install ant的時候遇到以下的錯誤：

--> Finished Dependency Resolution
java-1.4.2-gcj-compat-1.4.2.0-40jpp.115.x86_64 from installed has depsolving problems
  --> Missing Dependency: /usr/bin/rebuild-security-providers is needed by package java-1.4.2-gcj-compat-1.4.2.0-40jpp.115.x86_64 (installed)
Error: Missing Dependency: /usr/bin/rebuild-security-providers is needed by package java-1.4.2-gcj-compat-1.4.2.0-40jpp.115.x86_64 (installed)
 You could try using --skip-broken to work around the problem
 You could try running: package-cleanup --problems
                        package-cleanup --dupes
                        rpm -Va --nofiles --nodigest
The program package-cleanup is found in the yum-utils package.

解決方法是這樣的，把缺乏的jpackage-utils-compat-el5安裝進去即可：

rpm -Uvh http://plone.lucidsolutions.co.nz/linux/centos/images/jpackage-utils-compat-el5-0.0.1-1.noarch.rpm

或者是

rpm -Uvh https://github.com/downloads/pallet/pallet/jpackage-utils-compat-el5-0.0.1-1.noarch.rpm

Reference: plone

CentOS上安裝yasm

2012-07-01T20:37:00.001-07:00

rpm -Uhv http://apt.sw.be/redhat/el5/en/x86_64/rpmforge/RPMS/rpmforge-release-0.3.6-1.el5.rf.x86_64.rpm
yum -y update
yum -y install yasm

Reference: razuna

在CentOS上格式化XFS檔案系統

2012-06-22T01:58:00.004-07:00

yum install -y xfsprogs
mkfs.xfs -b size=4096 /dev/hda

如何看Homebrew某個Fomula所包含的版本

2012-06-21T09:17:00.000-07:00

以Maven為例

$ brew versions maven
#3.0.4    git checkout 1dc42b3 /usr/local/Library/Formula/maven.rb
#3.0.3    git checkout 14e4db3 /usr/local/Library/Formula/maven.rb
#3.0.2    git checkout 03b288a /usr/local/Library/Formula/maven.rb
#3.0.1    git checkout 83857d6 /usr/local/Library/Formula/maven.rb
#3.0      git checkout 09a0264 /usr/local/Library/Formula/maven.rb
#2.2.1    git checkout d40d419 /usr/local/Library/Formula/maven.rb

# install the specific version of Maven
# usage: brew switch [formula] [version]
brew switch maven 3.0.3
brew install maven

[Fixed] git push rejected (non-fast forward)

2012-06-20T19:54:00.002-07:00

下git push時遇到被reject的錯誤

$ git push origin master
To git@github.com:${USR}/mvn-repo.git
 ! [rejected]        master -> master (non-fast-forward)
error: failed to push some refs to 'git@github.com:${USR}/mvn-repo.git'
To prevent you from losing history, non-fast-forward updates were rejected
Merge the remote changes (e.g. 'git pull') before pushing again.  See the
'Note about fast-forwards' section of 'git push --help' for details.

只要先下git pull，在下git push就會正常了

$ git pull origin master
$ git push origin master

Reference: rip747