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How to attach bootable XFS filesystem volume to another instance on AWS EC2

noreply@blogger.com (Chirag Shah) — Thu, 22 Jul 2021 13:28:00 +0530

How to attach boot XFS filesystem volume to the instance

Create directory called bootDisk on the EC2 instance

sudo mkdir /bootDisk

sudo mount /dev/xvdf1 /bootDisk

Note: here you can replace /dev/xvdf1 with your attached harddisk path, you can find path by command "lsblk"

If volume mount fails then check dmesg | tail, if logs says conflict uuid then use option "nouuid" as below

sudo mount -o rw,nouuid /dev/xvdf1 /bootDisk

Change Date with Zone from terminal in linux

noreply@blogger.com (Chirag Shah) — Wed, 19 Nov 2014 12:00:00 +0530

date command is used for display date in terminal

you can use --set attribute for set time with zone

date --set="Wed Nov 19 01:11:00 EST 2014"

cat few lines from file from terminal in linux

noreply@blogger.com (Chirag Shah) — Wed, 19 Nov 2014 11:59:00 +0530

If you want to get 50 lines after line 7500 then you can get it by below command

sed -n '7500,+50p' filename

So here 7500 is the line from where i want to get lines
and 50 is the number of lines which i like to read

Command to check which service used how much memory on Linux

noreply@blogger.com (Chirag Shah) — Wed, 1 Oct 2014 10:58:00 +0530

Many linux users and new on linux users have an issue to know that which processes uses how much memory on his machine or on server, So they cant able to debug the memory issue on server

Here is the command which you can use to know that which services uses how much memory

ps -eo rss,pid,user,command --sort -size | awk '{ hr=$1/1024 ; printf("%13.2f Mb ",hr) } { for ( x=4 ; x<=NF ; x++ ) { printf("%s ",$x) } print "" }' | egrep -v 0.00

One more thing that might helps if you found more memory usage
Here is Command for clear cache
sudo sh -c "sync; echo 3 > /proc/sys/vm/drop_caches"

Hope this helps !!

Cheers

wkhtmltopdf: error while loading shared libraries: libXrender.so.1: cannot open shared object file: No such file or directory

noreply@blogger.com (Chirag Shah) — Wed, 1 Oct 2014 10:51:00 +0530

If you get this error while install wkhtmltopdf on centos/fedora then install below packages

1. yum install libXext libXrender fontconfig libfontconfig.so.1
2. yum install urw-fonts

Hope this helps !!

cheers

Install Ruby and Capistrano without Rails

noreply@blogger.com (Chirag Shah) — Tue, 23 Sep 2014 11:22:00 +0530

Below are the steps which you can follow to use capistrano deployment script to deploy any project

1. Install Curl
2. Install RVM by below curl (Ref: http://rvm.io/rvm/install)
   \curl -sSL https://get.rvm.io | bash -s stable   
3. source ~/.rvm/scripts/rvm
4. type rvm | head -n 1
5. rvm install 2.0.0
6. ruby -v
7. gem install capistrano (Ref: http://ryanflorence.com/deploying-with-capistrano-without-rails/)
8. gem install railsless-deploy

Gemset '' does not exist, 'rvm ruby-1.9.3-p547 do rvm gemset create ' first, or append '--create'.

noreply@blogger.com (Chirag Shah) — Fri, 29 Aug 2014 15:01:00 +0530

I get one error while try to install ruby 1.9.3 with rvm 1.25.28

rvm install 1.9.3

Error:
There was an error while trying to resolve rubygems version for 'latest'.
Halting the installation

rvm use 1.9.3

Error:
Gemset '' does not exist, 'rvm ruby-1.9.3-p547 do rvm gemset create ' first, or append '--create'.

To solve the above error
rvm use 1.9.3@newgemset --create --default

Hope this helps who install ruby 1.9.3 with rvm 1.25.28

Rails 4 Released !!!!!

noreply@blogger.com (Chirag Shah) — Fri, 28 Jun 2013 11:08:00 +0530

Hey guys,

Rails 4 final version is released on 25th june 2013

ITs pretty good :)

http://weblog.rubyonrails.org/2013/6/25/Rails-4-0-final/

Rails team recommend to use rails 4 with Ruby 2.0.0

Thanks to Rails core team again

uninitialized constant Rake::DSL with rails 3.2.x

noreply@blogger.com (Chirag Shah) — Mon, 3 Dec 2012 17:32:00 +0530

If you are using rake 0.8.7 and rails 3.2.x then you can do following as Rake::DSL is required in railties

So to solve this

module Rake
  module DSL
  end
end

noreply@blogger.com (Chirag Shah) — Fri, 23 Nov 2012 17:58:00 +0530

{ [Error: getaddrinfo ENOENT] code: 'ENOTFOUND', errno: 'ENOTFOUND', syscall: 'getaddrinfo' }

noreply@blogger.com (Chirag Shah) — Fri, 31 Aug 2012 17:07:00 +0530

You may get this error when you send request to any URL from nodejs,
Simply you can solve this error by doing following

1. Find out IP of url (which you try to access from your code)
2. Add that url and domain in your /etc/hosts as below
111.111.111.111 example.com

Cheers !!

Upgrade NodeJS

noreply@blogger.com (Chirag Shah) — Thu, 30 Aug 2012 13:10:00 +0530

Install node module 'n', this module helps nodejs version managements
Do as below

1. $npm install n -g
2. n 0.8.8

Its really awasome !!!

NodeJS Frameworks

noreply@blogger.com (Chirag Shah) — Fri, 22 Jun 2012 18:21:00 +0530

Best Frameworks for NodeJS

Find out more list for frameworks and others here
Difference between RailswayJS and TowerJS here

Install Node JS + NPM with RailswayJS or TownJS Framework

noreply@blogger.com (Chirag Shah) — Fri, 22 Jun 2012 18:16:00 +0530

Install Node and NPM

1. Add below to your ~/.npmrc file, create new if doen't exiest
root = /home/YOUR-USERNAME/.local/lib/node_modules
binroot = /home/YOUR-USERNAME/.local/bin
manroot = /home/YOUR-USERNAME/.local/share/man
2.Download Node.JS and install it under your ~/.local
tar -xvzf node.tar.gz
cd node
./configure --prefix=~/.local
make
make install
3. cd
ln -s .local/lib/node_modules .node_modules
4.which npm
If it says ~/.local/bin/npm, you're done.
Otherwise do as below.
export PATH=$HOME/.local/bin:$PATH
5.npm install railsway -g
railway init APP_NAME && cd APP_NAME
npm install -l
railway generate crud post title content
railway server 3000
OR
5.npm install tower -g
tower new app
cd app
tower generate scaffold Post title:string body:text belongsTo:user
tower generate scaffold User email:string firstName:string lastName:string hasMany:posts
node server

Ref: http://tnovelli.net/blog/blog.2011-08-27.node-npm-user-install/

     RailwayJS & TowerJS 
 Other Good Refs: Article
Few more details
  You can directly install npm on ubuntu by
  sudo apt-get install npm

For Fedora
1. git clone http://github.com/isaacs/npm.git
2. cd npm
3. sudo make install
Ref: http://drumcoder.co.uk/blog/2011/sep/11/installing-npm-fedora-14/
http://johnroach.info/2011/11/20/installing-node-js-0-6-2-on-fedora-16/

Install Mongodb on ubuntu / fedora 11 to 16

noreply@blogger.com (Chirag Shah) — Fri, 16 Mar 2012 12:15:00 +0530

Easy installation of mongodb on ubuntu and fedora

Ubuntu

   1. Add Repo Key as
        sudo apt-key adv --keyserver keyserver.ubuntu.com --recv 7F0CEB10

   2. Add Repo Source
for Debian Lenny or older ubuntu add below line to /etc/apt/sources.list

deb http://downloads-distro.mongodb.org/repo/debian-sysvinit dist 10gen

      for recent ubuntu add below line to /etc/apt/sources.list

    deb http://downloads-distro.mongodb.org/repo/ubuntu-upstart dist 10gen

   3. Install mongo-db

   sudo apt-get install mongodb-10gen

Fedora

  1. logged in as root user by su -
  2. Add below part to /etc/yum.repos.d/10gen-mongodb.repo

10gen]
name=10gen Repository
baseurl=http://downloads-distro.mongodb.org/repo/redhat/os/i686
gpgcheck=0

    3. yum install mongo-10gen mongo-10gen-server
4. Configure MongoDB Database Server as below
         1. nano -w /etc/mongod.conf
         2. Set or check the basic setting before start mongodb

             make sure that this below things are available in mongodb.conf

                  logpath=/var/log/mongo/mongod.log
                  port=2701
                  dbpath=/var/lib/mongo
     5. /etc/init.d/mongod start

   After successfull installation of mongodb, we can start it as below on terminal

   1. mongo
   2. use database_name # default

change table column name in Rails validation message

noreply@blogger.com (Chirag Shah) — Tue, 20 Sep 2011 18:09:00 +0530

class Vendor < ActiveRecord::Base

validate_uniqness_of :gid, :message => "should be uniq"

HUMANIZED_ATTRIBUTES = {
    :gid => "vendor"
  }

  def self.human_attribute_name(attr)
    HUMANIZED_ATTRIBUTES[attr.to_sym] || super
  end

end

Collect all child elements javascript

noreply@blogger.com (Chirag Shah) — Fri, 8 Jul 2011 16:49:00 +0530

For all first level children
var children = document.getElementById('id').childNodes;

For all descendants
var children = document.getElementById('id').getElementsByTagName('*');

For some particular element children
var childNodeArray = document.getElementById(tbody).getElementsByTagName('tr');

find process id for the port

noreply@blogger.com (Chirag Shah) — Mon, 28 Mar 2011 16:26:00 +0530

Find port by following way

lsof -w -n -i tcp:8080
fuser -n tcp 8080

Now you have some integer value which is the process of the port
Now kill it by
kill -9 XXXX

Debuging Technique with Ruby on Rails

noreply@blogger.com (Chirag Shah) — Sat, 26 Mar 2011 11:08:00 +0530

There are multiple debug techniques are available with RoR, Please use the
below techniques as much as you can, while you do programming in RoR.

1. install ruby-debug
   then need to start application by ruby script/server --debugger
   And place word 'debugger' anywhere in your code and once you run your
application, it stops running from where you have placed 'debugger'. We
can say that debugger is the breakpoint

Then you can use following commands
n - move next line
l - display the current line after the debugger
c - continue
You can also check the readme of the ruby-debug

2. You can use puts,exit etc.

3. You can use logger.debug "The object is #{@object}" or
RAILS_DEFAULT_LOGGER.debug @object

4. In view, you can also use <%=debug @object %>

5. You can simultaneously check your log by running tail -f lod/development.log in the another terminal or you can also use tail -n log/development.log where n is any numeric number

6. We can use Exception Notifier plugin in our production environment so that we gets an notification mail if any error occurs on production

Call Rake task from migration

noreply@blogger.com (Chirag Shah) — Mon, 24 Jan 2011 12:18:00 +0530

You can call the rake task in migration by writing following

Rake::Task[this_is_rake_task'].invoke

Is the string has numeric value?

noreply@blogger.com (Chirag Shah) — Mon, 24 Jan 2011 12:16:00 +0530

for check the string has numeric value or not then you can do it by below
s = "123cs"

then call method as below
is_numeric?(s)

and the method is as below
def is_numeric?(s)
s.to_s.match(/\A[+-]?\d+?(\.\d+)?\Z/) == nil ? false : true
end

Run your rails application with apache2 and mongrel_clusters

noreply@blogger.com (Chirag Shah) — Mon, 24 Jan 2011 11:25:00 +0530

Run your rails application with apache2 and mongrel_clusters

Install Apache 2.2 and enable the needed modules (url rewriting, proxy, proxy_balancer e proxy_http)

sudo apt-get install apache2

# enable your modules in apache
sudo a2enmod rewrite
sudo a2enmod proxy
sudo a2enmod proxy_balancer
sudo a2enmod proxy_http
sudo a2enmod proxy_connect

# if you not enabled any of the modules then may be errors occured while you restart your apache after adding the below configration
# Error may be encoutered it yoou have not enabled module rewrite is "Invalid command 'RewriteEngine', perhaps misspelled or defined by a module not included in the server configuration"

Install Mongrel, create a mongrel user, create the mongrel cluster
sudo gem install daemons gem_plugin mongrel mongrel_cluster --include-dependencies

You can continue with the same linux user to mongrel if you want otherwise you can create new user by
sudo /usr/sbin/adduser mongrel
This line creates new user mongrel withg same mongrel group
Now need to create one mongrel_cluster.yml
sudo mongrel_rails cluster::configure -e production -p 3010 -N 2 -c /home/user/projects/myapp -a 127.0.0.1 --user mongrel --group mongrel

here -e = your working environment
     -p = your port for run application
     -N = Number of instances of the application. here 2 instances for my application and port is 3010. so this application will work on 3010 and 3011 port
--user = need to provide your linuxuser
--group = need to provide your linuxgroup

this line will create /config/mongrel_cluster.yml file with following command
user: mongrel
cwd: /home/user/projects/myapp
log_file: log/mongrel.log
port: "3010"
environment: production
group: mongrel
address: 127.0.0.1
pid_file: tmp/pids/mongrel.pid
servers: 2

now make sure that tmp and log folder has permission to the user/group which you have user in mongrel_cluster if not assign permission by
sudo chown -R mongrel:mongrel /path/to/app/tmp

# Now start mongrel clusters
sudo mongrel_rails cluster::start

Hopefully clusters is worked perfactly and you can get it run on multiple port 3010 and 3011
http://127.0.0.1:3010
http://127.0.0.1:3011

Now need to set proxy balancer for this app
For this need to create one host for you app
Go to sudo nano /etc/hosts

127.0.0.1 localhost
127.0.0.1 myapp

Now need to configure Apache configuration file (sudo gedit /etc/apache2/sites-available/default).

NameVirtualHost *:80

#we need this as on Ubuntu/debian by default Proxy is not allowed
<Proxy *>
Order allow,deny
Allow from all
</Proxy>

#Proxy balancer section (create one for each ruby app cluster)
<Proxy balancer://myapp_cluster>
    BalancerMember http://myapp:3010
    BalancerMember http://myapp:3011
</Proxy>

#Virtual host section (create one for each ruby app you need to publish)
<VirtualHost *:80>
   ServerAdmin webmaster@localhost
        ServerName myapp
        DocumentRoot /home/user/projects/myapp/public/
    <Directory />
       Options FollowSymLinks
       AllowOverride None
    </Directory>
    <Directory /home/debian/chirag/mycalltime/public/>
       Options Indexes FollowSymLinks MultiViews
       AllowOverride All
       Order allow,deny
       allow from all
    </Directory>

   ScriptAlias /cgi-bin/ /usr/lib/cgi-bin/
    <Directory "/usr/lib/cgi-bin">
       AllowOverride None
       Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch
       Order allow,deny
       Allow from all
    </Directory>

   ErrorLog /var/log/apache2/error.log

   # Possible values include: debug, info, notice, warn, error, crit,
   # alert, emerg.
   LogLevel warn

   CustomLog /var/log/apache2/access.log combined

    Alias /doc/ "/usr/share/doc/"
    <Directory "/usr/share/doc/">
        Options Indexes MultiViews FollowSymLinks
        AllowOverride None
        Order deny,allow
        Deny from all
        Allow from 127.0.0.0/255.0.0.0 ::1/128
    </Directory>

#Rewrite stuff
RewriteEngine On

# Check for maintenance file and redirect all requests
RewriteCond %{DOCUMENT_ROOT}/system/maintenance.html -f
RewriteCond %{SCRIPT_FILENAME} !maintenance.html
RewriteRule ^.*$ /system/maintenance.html [L]

# Rewrite index to check for static
RewriteRule ^/$ /index.html [QSA]

# Rewrite to check for Rails cached page
RewriteRule ^([^.]+)$ $1.html [QSA]

# Redirect all non-static requests to cluster
RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_FILENAME} !-f
RewriteRule ^/(.*)$ balancer://myapp_cluster%{REQUEST_URI} [P,QSA,L]

</VirtualHost>

After configure the default file need to restart apache
sudo /etc/init.d/apache2 restart

Cheers....
You get your app running on multiple instanses with proxy balancer
http://myapp

search gem from repository

noreply@blogger.com (Chirag Shah) — Tue, 10 Aug 2010 17:29:00 +0530

If you want to find a gem in the repository then you can do it by following way

gem1.8 list -r | grep gem_name

Unpacked gem authlogic-2.1.3 in vendor/gems has no specification file. Run 'rake gems:refresh_specs' to fix this.

noreply@blogger.com (Chirag Shah) — Wed, 30 Jun 2010 14:12:00 +0530

You can solve this issue by following way

> cd vendor/gems/authlogic-2.1.3
> gem specification authlogic > .specification

cheers,

Get Session Data Available in Models - Ruby on Rails

noreply@blogger.com (Chirag Shah) — Thu, 24 Jun 2010 12:41:00 +0530

Sometimes we really need session variables inside model. But as the rails framework defines (MVC) pattern.

This pattern separates the context of the Web Application (Controller,View) from the Model. Model contains business logic of the web application. The Controller handles the interactions between the View and the Model.

So you can not access sessions directly in your model. You can crack it by following way.

Create one module

module Utility
  def current_user
    Thread.current[:user]
  end
 
  def self.current_user=(user)
    Thread.current[:user] = user
  end
end

Add following in application controller

class ApplicationController < ActionController::Base
  include Utility
  before_filter :set_user_session
 
  protected
  def set_user_session
    Utility.current_user = session[:user]
  end
end

And now get it in your model

class Account < ActiveRecord::Base
  include Utility

  def before_create
    unless allowed?(current_user)

      return false

    end
  end
end