10 most used Linux Distributions

10 most used Linux Distributions

1. Ubuntu: This is probably the most user-friendly Linux distribution ever made. It’s very well done. Some power users don’t like it because they say its “too user friendly”, but most people seem to be very happy with it. I have used several different versions of Ubuntu, and I have nothing bad to say about it. This is a great distro.

Now stop reading, and go download one (if not all) of these Linux distributions. Are you still running Windows? Why? Linux is free and it’s better.

2. CentOS: Previous to Fedora, Red Hat made one Linux distro, it was simply called Red Hat Linux, and it was free. Later they split their efforts into two distros, Fedora, and RHEL (Red Hat Enterprise Linux). Fedora is still free, but RHEL has to be licensed. CentOS is the unofficial free version of RHEL. It is not supported by Red Hat, but has the same code base.

3. Fedora: Red Hat’s open project, Fedora, has long been a favorite of Linux users worldwide. Started in 2003, it is their free alternative to RHEL. While RHEL is marketed at enterprises, Fedora is targeted at home users, with a slightly different look and feel.

4. OpenSUSE: This is one of my personal favorites. I’ve always love the SUSE interface. The first version of SUSE that I used was version 8, and it was this distro that made me realize how cool Linux really was. SUSE was acquired by Novell in 2003. Shortly after the acquisition, they followed the “Red Hat Model” and split their offerings in two. OpenSUSE is the free version of Novell’s SUSE Linux Enterprise platform.

5. Debian: This is a solid distro! Period.

6. Mandriva: Years ago, this distro was called Linux Mandrake. This was one of the first Linux distros marketed at everyday users. It is very easy to use. I installed it several years ago, but haven’t used it recently.

7. Linux Mint: I’ve never used this one, but I’ve heard nothing but good things about it. The interface looks very slick and intuitive. I’m anxious to try it out.

8. PCLinuxOS: Next to Ubuntu (scroll down a bit to read about Ubuntu), this is probably the most user-friendly Linux distribution. In some ways, its actually more friendly than Ubuntu. This is a great distro for newcomers!

9. Slackware: This one has been around longer than any other Linux distro, since 1992. It’s marketed mostly at power users because its interface is less friendly than some of the others, but it is still a rock solid distro! It has certainly stood the test of time.

10. Gentoo: I installed this several years ago. It was the most customizable version of Linux I’d ever seen. The installer actually complied the source code specifically for your computer. It was so meticulous it was almost annoying. I hear they’ve changed this in recent releases though. It remains a very popular distro.

What is Distro (plural Distros) ?
(Internet, software) A set of software components, typically (but not necessarily) open source components, that have been packaged into a larger product or component for distribution to end-users. A shortened version of the word “distribution.” Distro means a version of Gnu&Linux or other OpenSource Operating System although some people would argue that the term should include the various Windows and Apple OSes

Most Used Linux System Monitoring Tools Every Linux Admin Should Know

Most Linux System Monitoring Tools Every Linux Admin Should Know

1. Ping IP Address/ Website
To check that IP address or website accessible or not.

2. setup
To change admin tools

3. top – Process Activity Command

The top program provides a dynamic real-time view of a running system i.e. actual process activity. By default, it displays the most CPU-intensive tasks running on the server and updates the list every five seconds.

The top command provides several useful hot keys:

Hot Key Usage
t Displays summary information off and on.
m Displays memory information off and on.
A Sorts the display by top consumers of various system resources. Useful for quick identification of performance-hungry tasks on a system.
f Enters an interactive configuration screen for top. Helpful for setting up top for a specific task.
o Enables you to interactively select the ordering within top.
r Issues renice command.
k Issues kill command.
z Turn on or off color/mono

=> Related: How do I Find Out Linux CPU Utilization?

4. vmstat – System Activity, Hardware and System Information

The command vmstat reports information about processes, memory, paging, block IO, traps, and cpu activity.
# vmstat 3

Sample Outputs:

procs ———–memory———- —swap– —–io—- –system– —–cpu——
r b swpd free buff cache si so bi bo in cs us sy id wa st
0 0 0 2540988 522188 5130400 0 0 2 32 4 2 4 1 96 0 0
1 0 0 2540988 522188 5130400 0 0 0 720 1199 665 1 0 99 0 0
0 0 0 2540956 522188 5130400 0 0 0 0 1151 1569 4 1 95 0 0
0 0 0 2540956 522188 5130500 0 0 0 6 1117 439 1 0 99 0 0
0 0 0 2540940 522188 5130512 0 0 0 536 1189 932 1 0 98 0 0
0 0 0 2538444 522188 5130588 0 0 0 0 1187 1417 4 1 96 0 0
0 0 0 2490060 522188 5130640 0 0 0 18 1253 1123 5 1 94 0 0
Display Memory Utilization Slabinfo

# vmstat -m

Get Information About Active / Inactive Memory Pages

# vmstat -a

=> Related: How do I find out Linux Resource utilization to detect system bottlenecks?

5. w – Find Out Who Is Logged on And What They Are Doing

w command displays information about the users currently on the machine, and their processes.
# w username
# w vivek

Sample Outputs:

17:58:47 up 5 days, 20:28, 2 users, load average: 0.36, 0.26, 0.24
root pts/0 14:55 5.00s 0.04s 0.02s vim /etc/resolv.conf
root pts/1 17:43 0.00s 0.03s 0.00s w

6. uptime – Tell How Long The System Has Been Running

The uptime command can be used to see how long the server has been running. The current time, how long the system has been running, how many users are currently logged on, and the system load averages for the past 1, 5, and 15 minutes.
# uptime


18:02:41 up 41 days, 23:42, 1 user, load average: 0.00, 0.00, 0.00
1 can be considered as optimal load value. The load can change from system to system. For a single CPU system 1 – 3 and SMP systems 6-10 load value might be acceptable.

7. ps – Displays The Processes

ps command will report a snapshot of the current processes. To select all processes use the -A or -e option:
# ps -A

Sample Outputs:

1 ? 00:00:02 init
2 ? 00:00:02 migration/0
3 ? 00:00:01 ksoftirqd/0
4 ? 00:00:00 watchdog/0
5 ? 00:00:00 migration/1
6 ? 00:00:15 ksoftirqd/1
4881 ? 00:53:28 java
4885 tty1 00:00:00 mingetty
4886 tty2 00:00:00 mingetty
4887 tty3 00:00:00 mingetty
4888 tty4 00:00:00 mingetty
4891 tty5 00:00:00 mingetty
4892 tty6 00:00:00 mingetty
4893 ttyS1 00:00:00 agetty
12853 ? 00:00:00 cifsoplockd
12854 ? 00:00:00 cifsdnotifyd
14231 ? 00:10:34 lighttpd
14232 ? 00:00:00 php-cgi
54981 pts/0 00:00:00 vim
55465 ? 00:00:00 php-cgi
55546 ? 00:00:00 bind9-snmp-stat
55704 pts/1 00:00:00 ps
ps is just like top but provides more information.

Show Long Format Output

# ps -Al

To turn on extra full mode (it will show command line arguments passed to process):
# ps -AlF

To See Threads ( LWP and NLWP)

# ps -AlFH

To See Threads After Processes

# ps -AlLm

Print All Process On The Server

# ps ax
# ps axu

Print A Process Tree

# ps -ejH
# ps axjf
# pstree

Print Security Information

# ps -eo euser,ruser,suser,fuser,f,comm,label
# ps axZ
# ps -eM

See Every Process Running As User Vivek

# ps -U vivek -u vivek u

Set Output In a User-Defined Format

# ps -eo pid,tid,class,rtprio,ni,pri,psr,pcpu,stat,wchan:14,comm
# ps axo stat,euid,ruid,tty,tpgid,sess,pgrp,ppid,pid,pcpu,comm
# ps -eopid,tt,user,fname,tmout,f,wchan

Display Only The Process IDs of Lighttpd

# ps -C lighttpd -o pid=

# pgrep lighttpd

# pgrep -u vivek php-cgi

Display The Name of PID 55977

# ps -p 55977 -o comm=

Find Out The Top 10 Memory Consuming Process

# ps -auxf | sort -nr -k 4 | head -10

Find Out top 10 CPU Consuming Process

# ps -auxf | sort -nr -k 3 | head -10

8. Fdisk

9. iostat – Average CPU Load, Disk Activity

The command iostat report Central Processing Unit (CPU) statistics and input/output statistics for devices, partitions and network filesystems (NFS).
# iostat

Sample Outputs:

Linux 2.6.18-128.1.14.el5 (www03.nixcraft.in) 06/26/2009
avg-cpu: %user %nice %system %iowait %steal %idle
3.50 0.09 0.51 0.03 0.00 95.86
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sda 22.04 31.88 512.03 16193351 260102868
sda1 0.00 0.00 0.00 2166 180
sda2 22.04 31.87 512.03 16189010 260102688
sda3 0.00 0.00 0.00 1615 0
=> Related: : Linux Track NFS Directory / Disk I/O Stats

10. sar – Collect and Report System Activity

The sar command is used to collect, report, and save system activity information. To see network counter, enter:
# sar -n DEV | more

To display the network counters from the 24th:
# sar -n DEV -f /var/log/sa/sa24 | more

You can also display real time usage using sar:
# sar 4 5

Sample Outputs:

Linux 2.6.18-128.1.14.el5 (www03.nixcraft.in) 06/26/2009
06:45:12 PM CPU %user %nice %system %iowait %steal %idle
06:45:16 PM all 2.00 0.00 0.22 0.00 0.00 97.78
06:45:20 PM all 2.07 0.00 0.38 0.03 0.00 97.52
06:45:24 PM all 0.94 0.00 0.28 0.00 0.00 98.78
06:45:28 PM all 1.56 0.00 0.22 0.00 0.00 98.22
06:45:32 PM all 3.53 0.00 0.25 0.03 0.00 96.19
Average: all 2.02 0.00 0.27 0.01 0.00 97.70
=> Related: : How to collect Linux system utilization data into a file

11. mpstat – Multiprocessor Usage

The mpstat command displays activities for each available processor, processor 0 being the first one. mpstat -P ALL to display average CPU utilization per processor:
# mpstat -P ALL

Sample Output:

Linux 2.6.18-128.1.14.el5 (www03.nixcraft.in) 06/26/2009
06:48:11 PM CPU %user %nice %sys %iowait %irq %soft %steal %idle intr/s
06:48:11 PM all 3.50 0.09 0.34 0.03 0.01 0.17 0.00 95.86 1218.04
06:48:11 PM 0 3.44 0.08 0.31 0.02 0.00 0.12 0.00 96.04 1000.31
06:48:11 PM 1 3.10 0.08 0.32 0.09 0.02 0.11 0.00 96.28 34.93
06:48:11 PM 2 4.16 0.11 0.36 0.02 0.00 0.11 0.00 95.25 0.00
06:48:11 PM 3 3.77 0.11 0.38 0.03 0.01 0.24 0.00 95.46 44.80
06:48:11 PM 4 2.96 0.07 0.29 0.04 0.02 0.10 0.00 96.52 25.91
06:48:11 PM 5 3.26 0.08 0.28 0.03 0.01 0.10 0.00 96.23 14.98
06:48:11 PM 6 4.00 0.10 0.34 0.01 0.00 0.13 0.00 95.42 3.75
06:48:11 PM 7 3.30 0.11 0.39 0.03 0.01 0.46 0.00 95.69 76.89
=> Related: : Linux display each multiple SMP CPU processors utilization individually.

12. pmap – Process Memory Usage

The command pmap report memory map of a process. Use this command to find out causes of memory bottlenecks.
# pmap -d PID

To display process memory information for pid # 47394, enter:
# pmap -d 47394

Sample Outputs:

47394: /usr/bin/php-cgi
Address Kbytes Mode Offset Device Mapping
0000000000400000 2584 r-x– 0000000000000000 008:00002 php-cgi
0000000000886000 140 rw— 0000000000286000 008:00002 php-cgi
00000000008a9000 52 rw— 00000000008a9000 000:00000 [ anon ]
0000000000aa8000 76 rw— 00000000002a8000 008:00002 php-cgi
000000000f678000 1980 rw— 000000000f678000 000:00000 [ anon ]
000000314a600000 112 r-x– 0000000000000000 008:00002 ld-2.5.so
000000314a81b000 4 r—- 000000000001b000 008:00002 ld-2.5.so
000000314a81c000 4 rw— 000000000001c000 008:00002 ld-2.5.so
000000314aa00000 1328 r-x– 0000000000000000 008:00002 libc-2.5.so
000000314ab4c000 2048 —– 000000000014c000 008:00002 libc-2.5.so
00002af8d48fd000 4 rw— 0000000000006000 008:00002 xsl.so
00002af8d490c000 40 r-x– 0000000000000000 008:00002 libnss_files-2.5.so
00002af8d4916000 2044 —– 000000000000a000 008:00002 libnss_files-2.5.so
00002af8d4b15000 4 r—- 0000000000009000 008:00002 libnss_files-2.5.so
00002af8d4b16000 4 rw— 000000000000a000 008:00002 libnss_files-2.5.so
00002af8d4b17000 768000 rw-s- 0000000000000000 000:00009 zero (deleted)
00007fffc95fe000 84 rw— 00007ffffffea000 000:00000 [ stack ]
ffffffffff600000 8192 —– 0000000000000000 000:00000 [ anon ]
mapped: 933712K writeable/private: 4304K shared: 768000K
The last line is very important:

mapped: 933712K total amount of memory mapped to files
writeable/private: 4304K the amount of private address space
shared: 768000K the amount of address space this process is sharing with others
=> Related: : Linux find the memory used by a program / process using pmap command

13. netstat -rn

The command netstat displays network connections, routing tables, interface statistics, masquerade connections, and multicast memberships. ss command is used to dump socket statistics. It allows showing information similar to netstat. See the following resources about ss and netstat commands:

ss: Display Linux TCP / UDP Network and Socket Information
Get Detailed Information About Particular IP address Connections Using netstat Command

14. iptraf – Real-time Network Statistics

The iptraf command is interactive colorful IP LAN monitor. It is an ncurses-based IP LAN monitor that generates various network statistics including TCP info, UDP counts, ICMP and OSPF information, Ethernet load info, node stats, IP checksum errors, and others. It can provide the following info in easy to read format:

Network traffic statistics by TCP connection
IP traffic statistics by network interface
Network traffic statistics by protocol
Network traffic statistics by TCP/UDP port and by packet size
Network traffic statistics by Layer2 address

Fig.02: General interface statistics: IP traffic statistics by network interface

Fig.03 Network traffic statistics by TCP connection

15. tcpdump – Detailed Network Traffic Analysis

The tcpdump is simple command that dump traffic on a network. However, you need good understanding of TCP/IP protocol to utilize this tool. For.e.g to display traffic info about DNS, enter:
# tcpdump -i eth1 ‘udp port 53’

To display all IPv4 HTTP packets to and from port 80, i.e. print only packets that contain data, not, for example, SYN and FIN packets and ACK-only packets, enter:
# tcpdump ‘tcp port 80 and (((ip[2:2] – ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)’

To display all FTP session to, enter:
# tcpdump -i eth1 ‘dst and (port 21 or 20’

To display all HTTP session to
# tcpdump -ni eth0 ‘dst and tcp and port http’

Use wireshark to view detailed information about files, enter:
# tcpdump -n -i eth1 -s 0 -w output.txt src or dst port 80

16. strace – System Calls
Trace system calls and signals. This is useful for debugging webserver and other server problems. See how to use to trace the process and see What it is doing.

17. /Proc file system – Various Kernel Statistics

/proc file system provides detailed information about various hardware devices and other Linux kernel information. See Linux kernel /proc documentations for further details. Common /proc examples:
# cat /proc/cpuinfo
# cat /proc/meminfo
# cat /proc/zoneinfo
# cat /proc/mounts

18. Nagios – Server And Network Monitoring

Nagios is a popular open source computer system and network monitoring application software. You can easily monitor all your hosts, network equipment and services. It can send alert when things go wrong and again when they get better. FAN is “Fully Automated Nagios”. FAN goals are to provide a Nagios installation including most tools provided by the Nagios Community. FAN provides a CDRom image in the standard ISO format, making it easy to easilly install a Nagios server. Added to this, a wide bunch of tools are including to the distribution, in order to improve the user experience around Nagios.

19. Cacti – Web-based Monitoring Tool

Cacti is a complete network graphing solution designed to harness the power of RRDTool’s data storage and graphing functionality. Cacti provides a fast poller, advanced graph templating, multiple data acquisition methods, and user management features out of the box. All of this is wrapped in an intuitive, easy to use interface that makes sense for LAN-sized installations up to complex networks with hundreds of devices. It can provide data about network, CPU, memory, logged in users, Apache, DNS servers and much more. See how to install and configure Cacti network graphing tool under CentOS / RHEL.

20. KDE System Guard – Real-time Systems Reporting and Graphing

KSysguard is a network enabled task and system monitor application for KDE desktop. This tool can be run over ssh session. It provides lots of features such as a client/server architecture that enables monitoring of local and remote hosts. The graphical front end uses so-called sensors to retrieve the information it displays. A sensor can return simple values or more complex information like tables. For each type of information, one or more displays are provided. Displays are organized in worksheets that can be saved and loaded independently from each other. So, KSysguard is not only a simple task manager but also a very powerful tool to control large server farms.

How to Install & Configure Nagios On CENTOS/RHEL/FEDORA

Nagios is one of the popular open source system and network monitoring software application.Nagios let us monitor our IT infrastructure, be it servers, routers, switches or other devices.It monitor hosts and services and then alerting users when something wrong has been triggered. It is the powerful monitoring system that enables organizations to identify and manage IT infrastructure problems before they effect critical business processes.

Step to Install & Configuration


During portions of the installation you’ll need to have root access to your machine.

Make sure you’ve installed the following packages on your Fedora installation before continuing.

GCC compiler
GD development libraries

1- First install some tools : httpd, gcc, glib, glibc-common, gd and gd-devel

#yum install httpd php
#yum install gcc
#yum install glibc glibc-common
#yum install gd gd-devel

2- Create nagios user :

#/usr/sbin/useradd -m nagios
#passwd nagios
3- Add nagcmd group
#/usr/sbin/groupadd nagcmd
#/usr/sbin/usermod -a -G nagcmd nagios
#/usr/sbin/usermod -a -G nagcmd apache
4- Now go to http://www.nagios.org download files .

nagios-3.1.0.tar.gz nagios-plugins-1.4.13.tar.gz nrpe-2.12.tar.gz

#tar -zxvf nagios-3.1.0.tar.gz
#cd nagios-3.1.0
./configure –with-command-group=nagcmd
#make all; make install; make install-init; make install-config; make install-commandmode; make install-webconf
5- Edit your email admin address :

Go to

vi /usr/local/nagios/etc/objects/contacts.cfg

6- Create a nagiosadmin account for logging into the Nagios web interfaceassign to this you’ll need it later.

#htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin
enter the password.

7- Restart the httpd server :

#Service httpd restart
The second step : Extract and install plugins
1- Go to you downloaded nagios tools

#tar -zxvf nagios-plugins-1.4.13.tar.gz
2- cd nagios-plugins

./configure –with-nagios-user=nagios –with-nagios-group=nagios
make; make install
3- Now you have to add nagios to Chkconfig

chkconfig –add nagios
#chkconfig nagios on
4- Verify if you have a good config of nagios with the command

#/usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
5- Check if there are no errors displayed; then start nagios with command :

#service nagios start
To simplify the procesure please disable the selinux and iptables and ip6tables

now open your browser and http://localhost/nagios orr http://ip/nagios

Click on Screen-shots

Redhat/CentOS Mail Server Setup: Postfix, Dovecot, Virtual users, MySQL, SASL, Postfixadmin, TLS

Redhat/CentOS Mail Server Setup: Postfix, Dovecot, Virtual users, MySQL, SASL, Postfixadmin, TLS

This is a small guide, showing how to install postfix, dovecot and postfixadmin on a server running CentOS.

The components of an e-mail server are:
the delivery and reception service – Postfix, which handles mail delivery
the mail retrieval service, dovecot, which handles POP3 and/or IMAP mail retrieval
users database, storing usernames, passwords, mail location. In this guide, i’ll use a mysql database for this task
the SMTP authentication mechanism, to make possible e-mail delivery for roaming users.
the management interface: Postfixadmin. This is a very popular frontend used to manage users and passwods for e-mail systems, written for postfix in PHP. It is accessible through a web browser.
The TLS layer, used to encrypt communications between the SMTP/POP3 client and the server. It may be used for secure message delivery between servers, if both servers support TLS.
Installation on a CentOS server should be done in the following order:
– mysql database
– dovecot
– development tools (may be installed ino a development-only machine, the tools are required to rebuild the postfix package)
– postfix. The default postfix package do not support virtual delivery agent and mysql, so it must be recompiled
– postfixadmin

Steps to Mail Server Setup

1. MySQL Database installation
2. Dovecot installation and configuration
2.1. Dovecot SSL configuration
2.2 Dovecot configuration for multiple domains
3. Postfix installation and configuration
3.1. Postfix installation from centosplus repository
3.2. Postfix compiled with dovecot SASL and virtual users support
3.3. Postfix TLS configuration
3.4. Greylisting with postgrey
4. Postfixadmin installation

Difference between VMware Workstation, Player and Server

VMware Workstation, VMware Player and VMware Server seem like redundant products. However there are quite a few distinctions, that are quite apparent from their names already.
VMware Workstation is intended for “desktop use”, for a user who creates and edits Virtual Machines and uses them on his/hers desktop. It has features useful for product development that no other VMware product has such as integration with MS Visual Studio or VM teams, where the network between virtual machines in the team can be specified, including bandwidth and packet loss. VMware Workstation usually gets the new virtual hardware releases first and supports the widest guest OS range. It is optimized for interactive use and has some Direct3D (DirectX 9) and OpenGL capabilities. Workstation is not free. More information:


VMware Player is a stripped-down version of workstation, so it offers the same virtual hardware as Workstation. VMware Player 2.x and newer is free for non-commercial personal use only while Player 1.x had no such restriction. In the latest version it can both create and edit virtual machines while it earlier could only possible to run pre-built VMs. The performance of VMware Player is very similar to the performance of VMware Workstation. Even though Workstation 8 was released in September 2011, we are still waiting for VMware Player 4 to be released. For more info see here:


VMware Server is meant for creating and editing virtual machines and running server-like loads. It is optimized for IO rather than interactive use on the local terminal. Desktop intensive (graphical) applications will not have too good performance when viewed through the interface provided in VMware Server as all requests go through the network (even when you’re working locally). Server usually provides older or same generation of virtual hardware as Workstation or Player. Server is a free product, but note that VMware Server is declared End of General Support at 06/30/2011. More information:



VMware Server cannot be installed at the same time with Workstation/Player. This is most likely due to conflicting, different kernel modules and cannot be circumvented.

Note that even if this article says that the intended use is something, this does not mean that the product could not be used for something else. Just don’t expect Player to be a good Server or that you can play games on Server.