Cognitive Insight

SFTP to remote system using Virtual-IP

2008-09-22T13:44:00.000-07:00

SFTP programmatically without interruption to a remote-system that uses Virtual-IP (physical box is subjected to change) with the following options.

sftp -o PasswordAuthentication=no -o StrictHostKeyChecking=no

This will add the remote hostname to ~/.ssh/known_hosts file automatically without interruption.

Grep text recursively in Unix

2008-09-02T08:56:00.000-07:00

Using the pattern keyword:
grep pattern * */* */*/* 2>/dev/null

The simplistic approach using find is:
find /startdir -exec grep whatever {} dev/null \;

That's not necessarily very efficient. Using xargs can help
find . -name *.xml | xargs grep whatever

Using Mod_JK as Apache-Tomcat connector

2008-04-15T11:51:00.001-07:00

Apache runs securely on port 80. Tomcat runs securely on port 8080, which means that the default URL of your application will be something like http://mydomain.com:8080. With mod_jk, you can run Tomcat securely on it's normal port and have Apache forward requests to Tomcat. This will eliminate the 8080 from URL. Ref: Eapps User Guide to setup Tomcat

For instance: In Eapps hosting, these can be seen in the Custom Settings tab of the Website settings area, on the Site tab in your control panel.

JkMount /spring* ajp13
JkMount /* ajp13

This setting gets reflected in httpd.conf file.

Enable Sync Option for T-Mobile Moto Razr

2008-02-21T17:58:00.000-08:00

If you have a Motorola Razr phone from T-Mobile, you would have noticed that it lacks the sync option under Menu-Settings-Connection. Here is a hack I used to overcome the handicap.

Motorola RAZR V3 supports SyncML. However, T-Mobile apparently disabled that feature for their own versions of V3. Click here to get simple step-by-step guide in enabling it again. For guidance on how to do seem editing, refer to this page for instructions and screenshots.

Troubleshooting:
After connecting your Motorola phone to the PC, the P2Kman should be able to connect to it. If you do not have the correct driver installed, P2Kman can not detect the presence of your mobile phone. For Windows XP/Vista users, install the drivers from MotoX Forums to fix it.

Once the sync option is enabled on T-Mobile Moto Razr, you can use services like Zyb and GooSync to sync your mobile with various web services.

Switching SE Linux ON/OFF

2007-11-19T12:05:00.000-08:00

I had setup a CGI script on a linux box, and set all permissions right. Yet, I get a "403 Forbidden" page when I access the script via Apache web server. On digging, here is what I found...

Fedora Core 3 introduced the concept of security contexts as part of the Security Enhanced Linux (SELinux) definition. A Web page may have the right permissions, but the Apache httpd daemon won't be able to read it unless you assign it the correct security context or daemon access permissions. Context-related configuration errors will give "403 Forbidden" browser messages. Click here to learn how to setup the security context.

To avoid the hassle of setting up a security context, we can just turn OFF the SE Linux mode.
To view the mode: $ getenforce

To turn OFF the SE Linux mode
$ setenforce Permissive
$ vi /etc/sysconfig/selinux ; Set the property 'SELINUX' to disabled or permissive

To turn ON the SE Linux mode:
$ setenforce Enforcing
$ vi /etc/sysconfig/selinux ; Set the property 'SELINUX' to enforcing

Upcoming

2007-11-14T16:12:00.000-08:00

Here is what I'm up to... Some of the technologies that I will begin to play with include:

Groovy & Grails : This will help me to quickly build a prototype of what I wanted. Its very useful to test the waters before diving in.
SOA : I'm looking at OSGI (implemented by Equinox) and Oracle's platform for OSGI. This knowledge is crucial in order to architect a Software system.
Various Unit Test frameworks
New features of Java 1.5, 1.6, 1.7 : Purely for the purpose of Coding
Security aspects offered by Java & Enterprise Java

Look forward for posts revolving around the above topics soon...

UPDATE: The list of resources I am using to learn the above tech stuff are ...
The official Groovy Documentation beginning with 'Getting Started Guide'
A free ebook 'Getting started with Grails'

Bulk rename in Unix

2007-10-31T12:50:00.000-07:00

To change .htm files to .html
$for file in *.htm ; do mv $file `echo $file | sed 's/$.*\.$htm/\1html/'` ; done

Large deletes in Unix

2007-10-31T12:20:00.000-07:00

If there are too many files to be deleted at once, the 'rm -f' command does not work. It throws up an error that states "/bin/rm: Argument list too long". So, here is a solution...

$find -name '*.txt' -exec rm -f {} \;

Here we find each entry that matches the pattern *.txt, and execute the command rm -f on it.
Courtesy: Thanks to my team lead for this tip.

Crash the kernel

2007-10-03T08:47:00.000-07:00

To crash the UNIX kernel, type the following on its command prompt...
$ echo c > /proc/sysrq-trigger

Start Unix processes on bootup

2007-08-16T09:51:00.001-07:00

The chkconfig command can be used to activate and deactivate services, and configure a service to start during bootup.

$ chkconfig --list <service name>

To activate[deactivate] the service during bootup:

$ chkconfig --level 2345 <service name> on[off]

Logs for Redhat Clusters

2007-08-16T09:31:00.001-07:00

del.icio.us tags: redhat, linux, cluster, log

The log data for clustering is usually seen at /var/log/messages. We can edit settings, so that clustering can have its own log files (say /var/log/cluster). Open /etc/syslog.conf and append the following:

# Log cluster event logs to /var/log/cluster
daemon.* /var/log/cluster

Additionally, we can log-rotate to rotate /var/log/cluster. Open /etc/logrotate.d/syslog.conf and append the log file name.

Refer to this knowledge base article for how-to, http://kbase.redhat.com/faq/FAQ_85_7763.shtm

Enable php scripts in html

2007-03-12T13:28:00.000-07:00

For Godaddy hosting, include the following line in .htaccess file.

AddHandler x-httpd-php5 .html

This tells the server to treat all files with extension .html as PHP5 files. So now, you can add any php code to your html pages.

Linux Xterm from Windows

2007-03-07T09:52:00.000-08:00

This shows you how you can access Linux Xterm from Windows using Putty & Cygwin.

Open Cygwin, and execute /usr/X11R6/bin/startxwin.bat. This will start your local X-Server. You may use any other equivalent X-Server too.

Then, open & configure Putty as follows:
Connection > SSH > X11: Check "Enable X11 forwarding"

Thats it! The XTerm is enabled. Open the remote machine prompt using putty.

Tips:
When installing Cygwin for the first time, setup.exe does not install every package. Only the minimal base packages from the cygwin distribution are installed by default. You can add Cygwin/X to your installation by running setup, and selecting the 'xorg-x11-base' package from the 'X11' category.

Helpful resources:
Cygwin/X
Connecting to Linux lab remotely

First Post

2007-03-05T15:04:00.000-08:00

Testing my first post... I chose the name "Cognitive Insight" for this blog after some deep thinking. My other options included "Learning tree" and "Concrete Experience".

BTW, below is an excerpt about the learning process.

Bloom's Taxonomy divides the learning process into a six-level hierarchy, where knowledge is the lowest order of cognition and evaluation is the highest:
Knowledge is the memory of previously-learnt materials such as facts, terms, basic concepts and answers.
Comprehension is the understanding of facts and ideas by organization, comparison, translation, interpretation, and description.
Application is the use of new knowledge to solve problems.
Analysis is the examination and division of information into parts by identifying motives or causes. A person can analyze by making inferences and finding evidence to support generalizations.
Synthesis is the compilation of information in a new way by combining elements into pattern or proposing alternative solutions.
Evaluation is the presentation and defense of opinions by making judgments about information, validity of ideas or quality of work based on a set of criteria.