Installing the Operating System

CentOS Setup

We are re going to install a minimal CentOS 7 distribution. You can get a copy of the .iso the image used for the installation here.

If the previous link is not working, you may want to check for the latest release .

Boot up the installation DVD and start the CentOS 7 Installation wizard.

You may want to customize at least these items:

• Keyboard: choose the keyboard layout

• Networking: configure your network interface according to your infrastructure; you can either set it to DHCP to automatically get all the settings from a local DHCP server or configure it by hand.

• Select Date & Time: set appropriate Date and Time settings. Enable NTP synchronization to periodically get date and time settings from CentOS servers

• Installation Destination: select the hard disk where CentOS will be installed.

  You may select “Automatically configure partitioning” or configure the partitions by yourself. You may use the following partitioning scheme if you wish:

  Partition Label	Partition Type	Size	Mount Point
  boot	ext3	700 MB	/boot
  root	ext4	35 GB	/
  swap	swap	4 GB

• Click on Begin Installation

• Now set the password for the root user. Also click on User Creation to create the toor user (an unprivileged user).

• Wait for the installation process to finish, then reboot your machine

Network configuration

The network configuration should already be set, since it was set during CentOS setup stage.

You may want to review the configuration files

/etc/sysconfig/network-scripts/ifcfg-DEVICE

You may also want to review the file /etc/resolv.conf to check the nameservers.

Check that the connection is up by pinging an external server:

ping 8.8.8.8

Check that the DNS are properly configuring by pinging a host by its name:

ping google.com

Attention

Please note that in CentOS only ssh incoming connections are allowed; all other incoming connections are disabled by default.

In the paragraph related to the httpd service you can find details about how to enable incoming traffic.

Note that after configuring the network, you may continue installing the system setup using a ssh connection.

User access configuration

Login as root user and give the toor user administrative privileges by adding him to the wheel group:

usermod -aG wheel toor

SSH access

Allow SSH connections through the firewall

On CentOS 7 the firewall is enabled by default. To allow SSH clients to connect to the machine allow incoming connections on port 22:

firewall-cmd --zone=public --add-port=22/tcp --permanent
firewall-cmd --zone=public --add-service=ssh --permanent
firewall-cmd --reload

Disable SSH login for the root user

Warning

Before you disable root login make sure you are able to login via SSH with toor user account and you have the privileges to run sudo su to switch to the root user account.

Edit file /etc/ssh/sshd_config to disable root login via SSH:

PermitRootLogin no

Public key authentication

Public key authentication is generally considered a safer way to authenticate users for SSH access. Let’s set it up and disable password based authentication

First generate a public/private key pair using ssh-keygen:

ssh-keygen

Follow the procedure, you will end up with your newly generated key under ~/.ssh Now copy your public (by default it is called id_rsa.pub) key over the CentOS machine in /home/toor/.ssh/authorized_keys. There are several ways to do it, we are going to use the ssh-copy-id tool:

ssh-copy-id -i ~/.ssh/id_rsa.pub toor@<server-ip-address>

You should now be able to login via SSH as toor without been asked for the password:

ssh toor@<server-ip-address>

You can now disable password based login over SSH

Warning

Before disabling password authentication make sure you’ ve installed your public key on the server and you are able to login without password

Edit /etc/ssh/sshd_config as follows:

...
RSAAuthentication yes
...
PubkeyAuthentication yes
...
PasswordAuthentication no
...
UsePAM no
...

Installing ntp

Install the program for ntp server synchronization:

yum install ntp

Optionally, edit /etc/ntp.conf and add your own ntp servers before the first server directive. For instance, in Italy you may want to use the institutional time server:

server tempo.ien.it     # Galileo Ferraris

Replace tempo.ien.it with your nearest ntp server.

Sync with the server by issuing:

systemctl start ntpd

Set the time synchronization as an autostarting daemon:

systemctl enable ntpd

Installing base packages

Install:

yum install man
yum install vim
yum install openssh-clients    # also needed for incoming scp connections
yum install mc                 # mc (along with zip) can be used to navigate inside .war files
yum install zip unzip
yum install wget curl
yum install git