Skip to main content

Hardening the Linux server - Part 3

<< Part 2                                                                                                    Part 4 >>
Hardening the Linux server - Part 3

Write firewall rules
You can deny access to your server through your firewall. Ubuntu Server uses a firewall called Uncomplicated FireWall (UFW), which is actually a management tool for iptables. Iptables filters network packets based on a series of rules written by the system administrator. Iptables can be complicated for beginners, so UFW simplifies it. Using UFW can help you harden your server; but if you're truly interested in server security, learning how to write rules for iptables will let you fine-tune a server's security.
To get started with UFW, you need to install it. Follow these steps:
  1. From the command line, type sudo aptitude install ufw
  2. Press Enter and enter your password. Press Enter again to install the package.
  3. To enable the firewall, type the following: sudo ufw enable
  4. Press Enter. You see the message Firewall started and enabled on system startup. Now you can create rules for your firewall.
Remember how you changed the port for SSH earlier? To open the port through UFW by creating a rule, type the following at the command line:
# sudo ufw allow 65000
That command allows access over port 65000 and lets SSH traffic into your server.
To deny access over this port, use the following:
# sudo ufw deny 65000
To allow or deny traffic specifically on TCP port 65000, use the following command:
# sudo ufw allow 65000/tcp
You can also allow or deny traffic according by the protocol it uses. For instance, to block all HTTP traffic, you can use this command:
# sudo ufw deny http
You can create more complicated rules to deny or allow a service based on its IP address. For instance, if your desktop had the IP address and your server had an IP address of, you could allow only your computer's IP address the ability to establish an SSH connection:
# sudo ufw allow proto tcp from to 192.1681.5 port 65000
To check which rules you're currently running with UFW, use
# sudo ufw status
You're presented with a list of rules you've written for your firewall. If you see a rule that you wish to delete, type
# sudo delete [rule]

<< Part 2                                                                                                                 Part 4 >>


Popular posts from this blog

Shell Script: Find Number Of Arguments Passed

Many times , when we create shell scripts we try to do repetitive tasks through functions. Some functions take arguments & we have to check the no. of arguments that are passed to it.

Each bash shell function has the following set of shell variables:
[a] All function parameters or arguments can be accessed via $1, $2, $3,..., $N. [b] $* or $@ holds all parameters or arguments passed to the function. [c] $# holds the number of positional parameters passed to the function. [d] An array variable called FUNCNAME ontains the names of all shell functions currently in the execution call stack. ExampleCreate a shell script as follows: #!/bin/bash # Purpose: Demo bash function # ----------------------------- ## Define a function called test() test(){   echo "Function name:  ${FUNCNAME}"   echo "The number of positional parameter : $#"   echo "All parameters or arguments passed to the function: '$@'"   echo }
## Call or invoke the function ## ## Pass the parameters or a…

AMD Radeon™ HD 7670M on Ubuntu 12.04

Update:  Recently I install kubuntu 13.10 and there is no problem with graphics. It just works  fine out of the box.
I've seen many blog posts on how to make AMD HD7670M work on Ubuntu 12.04, specially when its in switchable graphics board like Dell Inspiron 15R 5520. I tried many things to make it work so that I could use the cinnamon desktop on ubuntu & other things too.. But to my surprise even the drivers from AMD site didn't work.
Then I tried a combination of those blog posts I read & somehow I became successful in running the full graphics including compiz settings inside My Ubuntu Machine.
Following are the steps I followed & it worked...
1. Create a backup of your xorg configuration file:
sudo cp /etc/X11/xorg.conf /etc/X11/xorg.conf.BAK
2. Remove/purge current fglrx and fglrx-amdcccle :
sudo apt-get remove --purge fglrx*
3. Install the driver:
sudo apt-get install fglrx fglrx-amdcccle
4. Install additional components for advanced graphics:
sudo apt-get install xvba-…

CentOS / Redhat : Configure CentOS as a Software Router with two interfaces

Linux can be easily configured to share an internet connection using iptables. All you need to have is, two network interface cards as follows:
a) Your internal (LAN) network connected via eth0 with static ip address
b) Your external WAN) network is connected via eth1 with static ip address  ( public IP provided by ISP ) Please note that interface eth1 may have public IP address or IP assigned by ISP. eth1 may be connected to a dedicated DSL / ADSL / WAN / Cable router: Step # 1: Enable Packet ForwardingLogin as the root user. Open /etc/sysctl.conf file # vi /etc/sysctl.conf
Add the following line to enable packet forwarding for IPv4: net.ipv4.conf.default.forwarding=1
Save and close the file. Restart networking: # service network restart
Step # 2: Enable IP masquerading
In Linux networking, Network Address Translation (NAT) or Network Masquerading (IP Masquerading) is a technique of transceiving network traffic through a router that involves re-writing the source and/or d…