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In this tutorial you will learn about Installing SSL Certificate (Secure Server Certificate) to secure communication between Postfix SMTP server and mail client such as Outlook or Thunderbird.
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Here is one of the most frequently asked questions from my mailbag:

Hey I need to know how much ram memory I have in my Ubuntu Linux computer. Under Windows XP I can find out memory by visiting Start > Control Panels > System in control panel. So how do I find out RAM information under Linux PC?

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Almost all new Linux wanna be guru (read as users who want to switch to Linux) asks a question:

I want to switch to Linux completely from Windows XP SP2. Which Linux version will be best - Redhat, SuSE, or other? I use my PC for:
Browsing Internet
Watching DVD / MP3
Writing CD/DVD

I’m also willing to spend a small amount of money if required to purchase Linux version.

Short answer is none. I can’t suggest *distro* name.

Long answer:
Linux is all about choice and freedom. There are different Linux distribution exists with different goals. It is good idea to define your goals and select Linux distribution as per your requirements.

I like Redhat and Debian for server as they are rock solid stable and comes with good binary packaging system. Some will swear up by Knoppix Live CD.

Some people like Suse and other recommends Ubuntu. There are others who like to compile everything from scratch (Gentoo).

  1. Consider following factors while selecting Linux:
    • Games
    • Your Linux skill level
    • Linux as server / network admin workstation
    • Running Linux on a new Hardware / Laptop
    • Running Linux on an older machine (486/PI/PII/Celeron)
    • Multilingual support (Hindi / Japanese language user interface)
    • Running Linux on Office PC for email and office work
    • Community support
    • Commercial support
  2. I recommend that you try out at least some different distributions. Go to distrowatch.com and look out What's Hot and What's Not
  3. Make sure your hardware is compatible with Linux. Download Live CD (list of all Live CD) and see if your hardware is compatible with Linux.
  4. Make sure good community support exists for your distro (for example check out Ubuntu community support forum)
  5. Get a good Linux book that teaches basis of Linux
  6. Learn how to use search engine to find out solution to the problems
  7. Learn to read man pages effectively and Linux commands to help you navigate
  8. Contact your nearest Linux user group (LUG) and see what other members recommends
  9. Ask a questions whenever in doubt, join Linux mailing lists and forums. When posting questions to a forum / newsgroup it is good idea to format the question and it's content in a proper way in order to get a good answer. Make sure you provide all information while posting a question. (See more guideline - how to ask questions the smart way)
  10. Finally you can always donate a small amount of money to your favorite distro and/or to any other open source project.

Further readings:

Surely, there are dozens of other reasons to select specific distro, so please do share your views and suggestions :D

If you try to mount an ext3 Linux filesystem on a SAN from multiple nodes at the same time you will be in serious deep trouble.

SAN based storage allows multiple nodes to connect to same devices at the same time. Ext3/2 are not cluster aware file system. They can lead to a disaster such as kernel panic, server hang, corruption etc.

You need to use something which supports:

  1. Useful in clusters for moderate scale out and shared SAN volumes
  2. Symmetrical Parallel Cluster File System, Journaled
  3. POSIX access controls

Both GFS (RedHat Global File System) and Lustre (a scalable, secure, robust, highly available cluster file system) can be used with SAN based storage allows multiple nodes to connect to same devices at the same time.

Many newbie get confused as Linux offers a number of file systems. This paper (Linux File System Primer) discusses these file systems, why there are so many, and which ones are the best to use for which workloads and data.

No Route to Host error and solution

I am getting error that read as No Route to Host. I am trying to ping my ISP gateway as well as DNS server but I am getting this error. How do I solve this problem?

This problem indicate networking conflicts or some sort of networking configuration problem.

Here are things to check:

Can you ping to your local router interface (such as 192.168.1.254)?

Make sure your card (eth0) is properly configured with correct IP address and router address. Use ifconfig command to configure IP address and route command to setup correct router address. If you prefer to use GUI tools:

  • redhat-config-network - Works on Red Hat and Fedora Linux/Cent OS.
  • network-admin - Debian and Other Linux distribution use this GUI too

Use above two GUI tools to setup correct IP address, DNS address and router address.

b) Make sure firewall is not blocking your access

iptables is default firewall on Linux. Run following command to see what iptables rules are setup:
# /sbin/iptables -L -n

You can temporary clear all iptables rules so that you can troubleshoot problem. If you are using Red Hat or Fedora Linux type command:
# /etc/init.d/iptables save
# /etc/init.d/iptables stop

If you are using other Linux distribution type following commands:
# iptables -F
# iptables -X
# iptables -t nat -F
# iptables -t nat -X
# iptables -t mangle -F
# iptables -t mangle -X

c) Finally make sure you are using a router and not a proxy server. Proxy servers are good for Internet browsing but not for other work such as ftp, sending ICMP request and so on.

See also:

Black Screen While Starting X window

My friend is new to Linux, everything was fine until he made some changes to X, which result into this problem. Now whenever he types command startx to start X he get a blank screen. Finally, he contacted me me via yahoo and asked me to get rid rid of this problem.

Step # 1: Reset blank X screen

First, get out of Blank screen by pressing combination of keys Ctrl+Alt+Backspace. If this fails, reboot system.

Step # 2: Reconfigure X server display

At shell, prompt type the following command to reconfigure X display.

If you are using Red Hat /Fedora / CentOS Linux type command:
# redhat-config-xfree86
If you are using Debian Linux type command:
# dpkg-reconfigure xserver-xfree86
OR login as the root user and type command:
# XFree86 -configure

Step # 3: Test new setup

Type startx to test your new settings:
# startx
OR if you used XFree86 –configure command to reconfigure X, then test it with following command:
# XFree86 -xf86config /etc/X11/XF86Config.new

See also:

Here is small script that does this. Debian or Ubuntu GNU/Linux does not comes with any SYS V init script (located in /etc/init.d directory) .

You create a script as follows and use it to stop or flush the iptables rules.

Please don't type rules at command prompt. Use the script to speed up work.

Procedure for Debian / Ubuntu Linux

A) Create /root/fw.stop /etc/init.d/fw.stop script using text editor such as vi:

#!/bin/sh
echo "Stopping firewall and allowing everyone..."
iptables -F
iptables -X
iptables -t nat -F
iptables -t nat -X
iptables -t mangle -F
iptables -t mangle -X
iptables -P INPUT ACCEPT
iptables -P FORWARD ACCEPT
iptables -P OUTPUT ACCEPT

(B) Make sure you can execute the script:
# chmod +x /root/fw.stop

(C) You can run the script:
# /root/fw.stop

A note for RedHat and friends Linux user

Please note that RedHat enterprise Linux (RHEL) and Fedora / Centos Linux comes with pre-installed script, which can be used to stop the firewall:
#/etc/init.d/iptables stop
Sample outputs: