View offline documentation of installed ruby gems

From command line, just run this -

$ gem server

This will start ruby documentation server on port 8088

previously it was

$ gem_server

which is now deprecated and may not work in your system

Installing Ruby On Rails on Ubuntu with rmagick

My laptop hard disk drive (it was a fujitsu drive on an HP Pavilion nobebook pc) was gone withing just two months of purchase. Later I got the replacement but, I had to spent another to prepare rails stack again :(
Anyway, here is the recipe for Ubuntu 7.10

$ sudo apt-get install ruby irb ri rdoc ruby1.8-dev libopenssl-ruby1.8 build-essential
$ wget http://rubyforge.org/frs/download.php/29548/rubygems-1.0.1.tgz
$ tar xzvf rubygems-1.0.1.tgz
$ cd rubygems-1.0.1
$ sudo ruby setup.rb
$ sudo ln -s /usr/bin/gem1.8 /usr/bin/gem
$ sudo gem update --system
$ sudo gem install rails
$ sudo gem install mongrel

I couldn't install rmagick on the first place. Because building rmagick (v2.3.0) requires ImageMagick version 3.0 or greater but current Ubuntu repository provides only v2.6 (by the time I wrote this). So, I had to install from the source. Thanks to Emmannual for this suggestion.
Remove ImageMagick, if you have already installed

sudo apt-get remove imagemagick

Now download, compile and install from the ImageMagick source

$ tar xvvzf ImageMagick.tar.gz
$ cd ImageMagick
$ ./configure –prefix=/usr
$ make
$ sudo make install
$ sudo gem install rmagick

Or alternatively, you can download binary of ImageMagick-dev from debian repo

$ sudo apt-get install libmagick9-dev
$ sudo gem install rmagick

One more step. Install all necessary gems that are required by the project you are working. Like, our current rails project uses the gem 'memcache-client'. So, I ran the following

$ sudo apt-get install memcached
$ sudo gem install memcache-client

Enable mod_rewrite in Apache under Ubuntu

'mod_rewrite' is disabled in default apache2 installation. To enable this, I followed following procedure. Thanks to Lavlu for showing me this.
At first, load mod_rewrite using Apache's mod enable command

# a2enmod rewrite

Then enable mod_rewrite from Apache2's configuration file. In default installation, there should be a 000-dafult file under /etc/apache2/sites-enabled directory. You should modify that. Just make the value 'All' (it should be 'None' by default) to AllowOverride key for '/' and '/var/www/' directory. So, the line will look like -

AllowOverride All

Now force reload Apache configuration

# sudo /etc/init.d/apache2 force-reload

Backing up mysql database and restore

This is also needed when you need to move your database elsewhere.
To backup your database -

mysqldump --user <mysql_username> --password=<mysql_password> <database> [<tablename>] > <output_filename>

To restore/initiate from the backup

mysql --user <db_username> --password=<db_password> <dbname> < <dump_file>