As I started to use Fedora 20 at work – by the way, a solid distro with all security features enabled, I had the bad surprise to get similar issues to those on OS X.
Again, we will have to face the joy of dependencies! Fedora provides Ruby 2.0 by default, so firing msfconsole would fail with many openssl warnings, ending with:

/usr/share/ruby/openssl/cipher.rb:61:in `': superclass mismatch for class Cipher (TypeError)
from /usr/share/ruby/openssl/cipher.rb:22:in `'
from /usr/share/ruby/openssl/cipher.rb:21:in `'
from /usr/share/ruby/openssl.rb:20:in `require'
from /usr/share/ruby/openssl.rb:20:in `'
from /opt/pentest/exploit/msf/lib/msf/ui/console/driver.rb:144:in `require'
from /opt/pentest/exploit/msf/lib/msf/ui/console/driver.rb:144:in `initialize'
from ./msfconsole:148:in `new'
from ./msfconsole:148:in `'

While the installation steps are globally the same than on Mac, there are some specific issues with rbenv and Postgresql.

Preparing Postgresql

Install:

 yum -y install postgresql-server postgresql-devel

Initiate a new “cluster” and connect to the sql client through the postgres user:

# as root:
postgresql-setup initdb
systemctl restart postgresql.service
su postgres psql

Inside the psql console, create the new Metasploit user and its database:

create user msf;
alter user msf with encrypted password 'super password';
create database msfdb;
grant all privileges on database msfdb to msf;
\q

Then, we will tell to Postgres how to accept local connections. ident necessitates an system account, trust means no password for any local account and md5 stands for a classic password authentication, which we will prefer.
Add this line inside /var/lib/pgsql/data/pg_hba.conf and beware that the order is important:

# IPv4 local connections:
host msfdb msf 127.0.0.1/32 md5
host all all 127.0.0.1/32 ident

Then we can restart the service and check with psql that the credentials are working:

systemctl restart postgresql.service
psql -U msf msfdb -h localhost
\q

Setting Ruby

Metasploit runs well with Ruby 1.9.3, so we will install this version and switch to it using rbenv.
rbenv does a nice job at managing several version of ruby next to each other, installing dependancies (as OpenSSL) and setting PATH:

# as root:
# download and install rbenv
\curl -sSL https://get.rvm.io | bash
rvm install ruby-1.9.3 --autolibs=packages
rvm use ruby-1.9.3
# checking, should obviously return ruby 1.9.3
ruby --version

Getting and running Metasploit

Install:

# as root in e.g. /opt
git clone https://github.com/rapid7/metasploit-framework.git msf
cd msf
yum -y install rubygem-bundler libpcap-devel
bundle install

Configure the database creating config/database.yml:

production:
    adapter: postgresql
    database: msfdb
    username: msf
    password: 
    host: 127.0.0.1
    port: 5432
    pool: 75
    timeout: 5

Launch it and have fun :

ln -s /opt/msf/msf* /usr/local/bin
sudo -i msfconsole
# as root
./msfconsole
# check connection to the database
db_status

Note that the -i option of sudo is mandatory, as it resets the environment for security purposes. That way it will get the environment of the target user, root, which should be just fine if you set rbenv with that user.

UPDATE 02/27/2014: I had some issues starting Metasploit with sudo and I actually failed to find a satisfying solution. I am now just launching it as root and in its work directory.

It is recommended to add a cron entry in /etc/crontab for regular updates:

# msfupdate every 2 hours
0 */2 * * * root /opt/msf/msfupdate 2>&1

Getting Metasploit

First, let’s fetch Metasploit. Adjust the last two lines by replacing .zshrc (I am using Zsh) with .bash_profile if you are using Bash, for instance.

This will download, create symlinks and set the database settings path (we will come back on it later) in your environment:

cd /usr/local/share/
git clone https://github.com/rapid7/metasploit-framework.git
cd metasploit-framework
for MSF in $(ls msf*); do ln -s /usr/local/share/metasploit-framework/$MSF /usr/local/bin/$MSF;done
ln -s /usr/local/share/metasploit-framework/armitage /usr/local/bin/armitage
echo export MSF_DATABASE_CONFIG=/usr/local/share/metasploit-framework/config/database.yml >> ~/.zshrc
source ~/.zshrc

Metasploit is almost ready, but don’t run anything yet. There a still quite a few steps…

Getting Postgres

We use Homebrew:

brew install postgresql --without-ossp-build

Initialization stuff:

initdb /usr/local/var/postgres

To have launchd start postgresql at login:

ln -sfv /usr/local/opt/postgresql/*.plist ~/Library/LaunchAgents

But I prefer to keep my startup clean, so I added two aliases in my .zshrc

alias pg_start='pg_ctl -D /usr/local/var/postgres -l /usr/local/var/postgres/server.log start'
alias pg_stop='pg_ctl stop'

So you now have two commands, pg_start and pg_stop, to use for Metasploit.
Finally, we create the msf user that will connect to the database from within Metasploit:

createuser msf -P -h localhost  
createdb -O msf msf -h localhost 

While we are at the database stuff, let’s configure Metasploit to use it. Create a database.yml file in  /usr/local/share/metasploit-framework/config/ and put these lines:

production:
    adapter: postgresql
    database: msf
    username: msf
    password: <password>
    host: 127.0.0.1
    port: 5432
    pool: 75
    timeout: 5

The database is ready!

Getting Ruby

The last big step is to install Ruby. The one provided by Mac Os is a little too old, and you don’t want to mess with system libraries, so let’s leave it untouched. You could install Ruby with Homebrew, but it happens that the latest version (2.0.0-p0) is not working with Metasploit (OpenSSL libraries conflicts). So we need to use something like the 1.9.3 version of Ruby.

Anyway, a good practice is to have some flexibility on the version you are going to use, so you would be able to switch between 1.9.3, 2.0.0 or whatever and that whenever you need.

Here comes rbenv. For the next steps, I will assume that you have a working homebrew setting.

Let’s go:

brew install rbenv ruby-build

Add this line to your .zshrc or bash_profile:

eval "$(rbenv init -)"

Now you should be able to list all installable versions of Ruby:

rbenv install --list

Let’s pick up 1.9.3:

rbenv install 1.9.3-p392

It takes a while, but after it is completed, you can set it as your default:

rbenv rehash
rbenv global 1.9.3-p392

Note that you could use the local command instead of global to set it for the current terminal only.

Let’s check that everything is correctly set. This is where the Ruby versions are stored:

$ ls ~/.rbenv/versions/
1.9.3-p392 2.0.0-p0

ruby and gem MUST point to the 1.9.3 version:

$ rbenv which ruby
$HOME/.rbenv/versions/1.9.3-p392/bin/ruby
$ rbenv which gem
$HOME/.rbenv/versions/1.9.3-p392/bin/gem

Looks good, let’s go ahead.

We are now able to install up the required gems for Metasploit. They made it easy by packaging these in a Gemfile that can be read by the “bundle” utility:

gem install bundle
cd /usr/local/share/metasploit-framework
rbenv rehash
bundle install

Final steps

Create an vncviewer wrapper to facilitate use from within Metasploit:

echo '#!/usr/bin/env bash'  >> /usr/local/bin/vncviewer   
echo open vnc://\$1 >> /usr/local/bin/vncviewer  
chmod +x /usr/local/bin/vncviewer

Get and compile the pcaprub library (optional):

cd /usr/local/share/metasploit-framework/external
git clone http://github.com/shadowbq/pcaprub.git
cd ./ext/pcaprub
ruby extconf.rb && make && make install

Have fun!

If you haven’t, don’t forget to start Postgres, and you are ready to play:

sudo -E msfconsole

It should deploy the database structure and then start to work without warning. Hurrah! That was not hard, but a bit long, wasn’t it?

In case it still fails for you, it means that something went wrong with the setup. Check the steps again, and then leave a comment as it may be the time for an update or a correction of this article.

Credits

As stated in the introduction, this article is mostly taken from darkoperator.com with minor adjustments (it actually did not work out of the box for me), so the use of rbenv. I hope it will be helpful to other people in the same case as me.

UPDATE 09/07/2013:

• change in pcaprub directory (./pcaprub –> ./ext/pcaprub)

UPDATE 07/23/2013:

• add missing rbenv rehash command (thanks @amukofes)
• add missing commands to retrieve pcaprub (thanks @Ton)
• fix indentation in postgres config file