Web Patrika

Here's how to export an existing database and import it into another database in postgres. 1. Login to a database machine as postgres user 2. use following to export database pg_dump database-name > filename-dump.out 3. Now create a new database in which the data will be imported, if it does not exist. createdb new-database-name 4. Now import the data into new database psql -f filename-dump.out new-database-name

One solution is to run sshd on a non-standard port. Most automated attacks only attempt to connect on port 22 and therefore, this can be an effective way to hide from many attackers. To configure this, just change the Port line in /etc/ssh/sshd_config and restart ssh as follows; vi /etc/ssh/sshd_config Port 922 <-- update port number and uncomment if the setting is commented /etc/init.d/sshd restart

Tiles is a great framework to organize site content by constructing a page using multiple tiles. It allows reuse and customization of site content. I ran into a problem of making tiles attribute visible to a nested tile. The attributes defined in tiles definitions are defined in tiles scope and hence only available to the tile associated with the definition. In order to make the attribute available to nested tiles, pass the attribute as follows; <tiles:insert attribute="header" ignore="true"> <tiles:put name="title" beanName="title" beanScope="tile"/> </tiles:insert> If there is a need to access the attribute in struts bean tags or JSTL use <tiles:useAttribute/> or <tiles:importAttribute/> tags in jsp to access the attribute as follows; <tiles:useAttribute name="title" /> You can now access the value of title attribute using struts bean tag <bean:write name="title" /> or usin...

If you get this error while connecting to a postgres database, most likely you are missing an entry in pg_hba.conf file to allow users from your machine to access the database. You will normally find the pg_hba.conf file in /var/lib/pgsql/data directory. If you don't find it there, look for PGDATA environment variable by doing a login to postgres server as a postgres user and typing env at command prompt. Then edit the file to add following entry ; host all all XYZ 255.255.255.255 trust just below the following entry host all all 127.0.0.1 255.255.255.255 trust and restart the postgres process by typing pg_ctl restart . It should now allow all user from your machine to connect to the database.

I was trying to use tomcat connection pooling to establish a connection to MySQL database. I ran into "Bad handshake" SQLException. After few minutes on internet, I figured out that it was a problem with the driver. However, when I checked WEB-INF/lib directory I found latest mysql driver already placed in that directory. However, I found another older MySQL driver in <tomcat-dir>/common/lib . So tomcat was loading the old driver from classpath ahead of latest drivers in WEB-INF/lib directory. Once I updated the old driver with the latest version, everything worked fine. Note: removing the driver from <tomcat-dir>/common/lib did not fix the problem since tomcat connection pool needs to load the driver from common library location.

In order to setup cron jobs for a user other than the root, use the following command which should open a file in vi editor that schedules cron job for that particular user. crontab -u <user> -e Later, if you wanted to view a list of cron jobs scheduled by a user, use the following command. crontab -u <user> -l

I noticed that a web application deployed on tomcat application server kept throwing JDBC exceptions after every couple of days. So I guessed that it must be a problem with mysql database connection timing out. I did quick search on the issue and found this article explaining the problem. You need to switch from the default Hibernate connection pooling to one of the production grade database connection pooling technology and set appropriate timeout settings. You will also need to create a c3p0.properties file containing following values; # a good mysql test query c3p0.preferredTestQuery=SELECT 1 c3p0.testConnectionOnCheckout=true

Following configuration in web.xml of a web application is useful for password protecting the web application in tomcat servlet engine. <security-constraint> <web-resource-collection> <web-resource-name>portalBase Application</web-resource-name> <url-pattern>/*</url-pattern> <!-- If you list http methods, only those methods are protected --> <http-method>DELETE</http-method> <http-method>GET</http-method> <http-method>POST</http-method> <http-method>PUT</http-method> </web-resource-collection> <auth-constraint> <role-name>role1</role-name> </auth-constraint> </security-constraint> <login-config> <auth-method>BASIC</auth-method> <realm-name>portalBase Application</realm-name> </login-config> <!-- Security roles referenced by this ...

Linux firewall can be managed using iptables command. I setup tomcat with Apache webserver in front using mod_jk2. But tomcat was still accessbile from port 8080. In order to disable direct access to port 8080 I executed following command. iptables -A INPUT -p tcp --dport 8080 -j REJECT You can review the above rule and any other existing rules as follows; iptables -L -n --line-numbers Now, if later you wanted to undo or remove a rule, use the above command to figure out the line number of the rule. A sample output from the previous command looks like below; Chain INPUT (policy DROP) num target prot opt source destination 1 LOG tcp -- 0.0.0.0/0 0.0.0.0/0 tcp flags:!0x16/0x02 state NEW LOG flags 0 level 4 prefix `NEW NOT SYN: ' 2 DROP tcp -- 0.0.0.0/0 0.0.0.0/0 tcp flags:!0x16/0x02 state NEW 3 DROP tcp -- 207.46.249.190 0.0.0.0/0 tcp 4 DROP tcp -- 0.0.0.0/0 ...

I was very comfortable using MySQL query and admin GUI tools to connect to MySQL database. However, recently I had to manage a database that was behind a firewall. I found these steps very useful to enable ssh tunneling (or forwarding) to access MySQL database behind the firewall using GUI tools. It is very easy to setup and only took couple of minutes.

Following command can be used to take a dump of an existing MySQL database. mysqldump db-name --host=host-name --user=user-id --password=user-pass > init-db.sql This will create a file called init-db.sql containing sql queries to reinitialize the database.

If you wanted to send emails to users but did not want to receive any replies to the email, you would need to setup a no-reply@domain.com email account. These kind of email ids are useful when sending emails containing forgotten passwords or activation code. Below are the steps for creating such account in Postfix. 1. Identify the file containing alias for Postfix First, make sure the following line in the ALIAS DATABASE section of the /etc/postfix/main.cf is NOT commented out: alias_maps = hash:/etc/aliases 2. Create an alias that redirects messages to /dev/null Edit /etc/aliases and add following entry devnull: /dev/null 3. Create a virtual email id Edit /etc/postfix/virtual and add following entry no-reply@domain.com devnull 4. refresh postfix alias and postfix cache Execute following commands. (You may require root privileges) > newaliases > postfix reload

Add following valve to tomcat server.xml to restrict access to the website from limited IPs. <Valve className="org.apache.catalina.valves.RemoteAddrValve" allow="127.0.0.1,xx.xxx.xxx.xx,xxx.xx.xxx.[6789].,xxx.xx.xx.xx.*,xxx.xx.xx.x[2345]., xxx.xx.xx.xx[4578]"/>

In order to capture session-id of user in tomcat access logs, use the following value for pattern attribute in AccessLogValve. pattern="%h %l %u %t "%r" %s %b "%{Referer}i" "%{User-Agent}i" %S" For more information, loook at AccessLogValve API documentation.

I was looking for a way to easily manage web application specific configuration in separate properties file. In our current version of application, a properties file was included in a war file of web application. However, this was problematic since the properties file had to be updated every time we deployed a new war file. I tried passing the name of the properties file in Tomcat command-line but that did not work well for multiple web applications. Then I came across Environment tags in Tomcat context definition that can be configured for each individual application. So I decided to us the following solution. 1. Add Environment entry for name of a properties file in context definition of web application. <Context path="/app1" docBase="C:/app1/web-dir" debug="0" reloadable="true"> <Environment name="appconfig" value="WebApp1.properties" type="java.lang.String" overri...

I misplaced my Motorola Razr and wanted to use my old Nokia phone in the mean time. So I went to a local operator outlet store and they gave me a new SIM card but refused to unlock the old phone. I also tried calling the customer service but got the same answer. So I did a search on google to see if any third-party could help me unlock the Nokia phone. That is when I came across Free SIM Unlock Nokia online . I was able to unlock my Nokia phone in a matter of few minutes without any issues. The steps were very precise and simple. I wonder if it is worth the time and money operators have to invest in enforcing this restriction, when the phones can be unlocked so easily.

Recently I came across an article that mentioned Pearl Crescent Page Saver extension for Firefox that allows users to save a snapshot of the website as an image. It is a very handy tool that lets you save either the visible portion of the website or the entire website to an image file. That is very helpful as I remember I had to use Paint tool to manually merge the snapshots of a website that did not fit all in one page.

In order to extract a column values from a text file where each line contains several words separated by space, following can be used; cut -d' ' -f6 file.txt > result.txt This would extract values from 6th column in a file named file.txt where each line contains words separated by white spaces.

Creating a user account is a two step process. 1. Create a user account. prompt> useradd user-name 2. set a password for the new account. prompt>passwd user-name This will create a user with a home directory /home/ user-name and default shell set to bash.

The clock can be set manually and using NTP service. 1. Manually: [root@server /root]# date 012621362007 Fri Jan 26 21:36:26 PST 2007 [root@server /root]# hwclock --utc --systohc [root@server /root]# 2. Using NTP service: Add the time server to /etc/ntp.conf and to /etc/ntp/step-tickers: /etc/ntp.conf: server 192.168.0.1 server 192.168.0.2 /etc/ntp/step-tickers 192.168.0.1 192.168.0.2 Then make sure that ntp will start at boot time: chkconfig --level 2345 ntpd on chkconfig --list ntpd And start the service: service ntpd start

To create a database; createdb [db-name] To get a psql prompt; psql [db-name] To export table data; pg_dump --data-only --table=table-name db-name > file-name Following commands can be executed at psql prompt. list all databases in postgres; \l list all tables in a database; \d execute a sql script; \i [sql-script]

A string consisting of one or more words can be replaced as follows. >cat file the black cat was chased by the brown dog >sed -e 's/black/white/g' file the white cat was chased by the brown dog A pattern can also be used for search string. For example following will replace entire string starting with 2007 until = symbol in a text. sed -e 's/^2007.*=/replacestring/' file