Linux comand for Network troubleshooting

Sometimes the admins and network engineers have to deal with a variety of problems on the network. I will share my experience about troubleshooting on the network by using 5 standard tool commonly used for troubleshooting the

    ping
    traceroute
    netstat
    telnet
    tcpdump
Ping. I'm sure most of the network admin and network engineer must know the ping command. ping is used to check network connectivity. Ping uses ICMP protocol. The format of the ping command:
ping nama_host / ip_address option
For example: ping 192.168.100.1-c 10 it will be to ping the ip 192.168.100.1 10 times.
Traceroute Traceroute is used to check or trace the route network. Suppose we try to ping www.yahoo.com and the result turned out to request time out To mnegetahui rupture in our network or network provider, then we use the traceroute command.
example traceroute: traceroute www.yahoo.com
Netstat Netstat is used to check the connection happen and open ports and can also be used to view the routing table. So with netstat we can know that we use computers or servers that we are setting the connections and open ports where port whatever
example netstat: netstat-an To see the connection in any direction
netstat-tpnl To view an open TCP port
Telnet. Telnet is used to check whether the port is accessible from any clien. eg port 25 and 110 checks For example telnet: telnet 10.2.86.75 25 25 to check smtp
telnet 10.2.86.75 25 110 to check pop3
Tcpdump. Tcpdump is used to extract data packets. By knowing the data packets that pass, we can identify whether there is something wrong such as a broadcast ip or ip who try to do activities that are not allowed
tcpdump examples: tcpdump-vv to perform packet sniffing tcpdump-i eth0 for sniffing packets on interface eth0 tcpdump host alinuxnews for sniffing host alinuxnews

Securing SSH server in Linux

Restrict ssh access to the server is a must because it involves security issues. Now I will share how to limit ssh into our server. Let's assume our server is a server D

1. Changing the ssh port for only us who know the server D
2. Prohibiting root login via ssh for security
3. Restrict ip addresses which can do ssh to the server D

To do the numbers 1 and 2 we can do it by editing the files in sshd_config.

To change the ssh port, change the number 22 to another number in the Port parameter 22. 22 is the default port for ssh service, and therefore replace it with another number such as 40

Port 40

To disallow root login, change the following parameter from NO to YES

PermitRootLogin yes

To limit the IP addresses that may access the server D then we should use / etc / host.allow and / etc / host.deny
in / etc / hosts.allow we must enter the ip address that are allowed to remotely

# pico / etc / hosts.allow

and enter the following parameters
sshd: 192.168.13.0/24 # # # if we want to allow network 192.168.13.0 to our server remotely via ssh D

if it is finished, save and edit the file / etc / host.deny

# pico / etc / hosts.deny

then edit and enter the following parameters

sshd: ALL # # # This will refuse all connections other than that you enter in / etc / hosts.allow

then save and exit

after that please restart your ssh sevice for configuration number 1 and 2 runs

Screen : shell command for making daemon process in Linux

Those who like to use terminal in Linux, usually already know how to make a process into a daemon. Some of us usually using the characters '&' after the command. Anyway that way has as weaknesess.  The weaknesses of the daemon by using the character is the difficulty in monitoring the log process or see the current process. Sometime we must create a program to produce a log file. It will be simple if the program is mad by your self, but if not? You will get dificulties and takes long time.

For that I now prefer to use a screen, a small program that really helped me. The way is simple, just type "screen", you will move to shadow of the console and press the space bar. In the new console you can type various another Linux commands. So, how do I return to the old terminal. Quite simple as well, press Ctrl A and D. Remember Ctrl A and D at the same time. Do not only press Ctrl D alone because Ctrl + D means that you turn off the screen of the terminal. If we have exit the screen, we can see a list of screen that we created with the command bellow :

screen-list

There are screens on:
     28694.pts-0.test (03/05/11 11:28:02) (detached)
     28479.pts-0.test (03/05/11 11:26:31) (detached)
     26057.pts-4.test (02/05/11 14:34:46) (detached)

If we want to return to the screen that we just created can we type the command bellow

screen-r numberscreen

example:
screen-r 28694

so from now on you can make the process as much as possible with the "screen" command.

Clonezilla : a Linux based software to duplicate hard disk

Last week I tried Clonezilla. I actually already know about Clonezilla few years ago, but have not had time to use it. I tried to make a duplicate of my laptop hard disk and the result is very satisfactory. All contents of the hard disk, MBR, and also boot loader are copied without being left behind.

Clonezilla is a software to copy the entire contents of your hard disk or just partition the hard disk to another hard disk. It also able to copy into an image. Clonezilla will copy all clusters and sectors from hard disk to another hardisk destination. If copied into the image, it will be bundled into an image file. Clonezilla is build based on Linux and is still a family with debian and ubuntu. To duplicate the contents of your hard disk you can use network booting or just use a USB media (such as external hard disk), IDE or SATA. The inmportance requirement is only media that are copied and the media to be copied must be equal or greater capacity.

If you copy the entire contents of your hard disk, then Clonezilla will copy the contents of the MBR and bootloader. So it can be used as as hot-swap hard disk. Which is as a hard disk or backup to your hard disk pc / laptop. If someday your hard disk laptop / pc get problems, then just swap the problem hard disk with the duplicate hard disk. There is no need to install the OS or other drivers.

Create Wallpaper slideshow in Linux

Wallpaper slideshow is one of the interesting features in the GNOME Desktop. We can enjoy the turn of the desktop within a certain timeframe. By default, Ubuntu has wallpaper slideshow with titles cosmos. Try it.

Now I will teach you how to make wallpaper slideshow manually, although it could just use a wallpaper slideshow application, which unfortunately is not my concern.

Well, prepare a few images as wallpaper and place it in a folder, for example, I put it in the folder / home / alinuxnews / Pictures / slidepaper of contents:
- 1.png
- 2.svg
- 3.jpg
- 4.jpg
- 5.jpg
- Slidepaper.xml

Let's open the file slidepaper.xml or you can open gedit, click new and save with slidepaper.xml name in the folder.
Copas my own code and modification of files / usr/share/background/cosmos/background-1.xml

Contents:

<background>

  <starttime>

    <year> 2011 </ year>

    <month> 01 </ month>

    <day> 01 </ day>

    <hour> 00 </ hour>

    <minute> 00 </ minute>

    <second> 00 </ second>

  </ Starttime>

<! - This animation will from the start at midnight. ->

  <static>

    <duration> 1795.0 </ duration>

    <file> / home/alinuxnews/Pictures/slidepaper/1.png </ file>

  </ Static>

  <transition>

    <duration> 5.0 </ duration>

    <from> / home/alinuxnews/Pictures/slidepaper/1.png </ from>

    <to> / home/alinuxnews/Pictures/slidepaper/2.svg </ to>

  </ Transition>

  <static>

    <duration> 1795.0 </ duration>

    <file> / home/alinuxnews/Pictures/slidepaper/2.svg </ file>

  </ Static>

  <transition>

    <duration> 5.0 </ duration>

    <from> / home/alinuxnews/Pictures/slidepaper/2.svg </ from>

    <to> / home/alinuxnews/Pictures/slidepaper/3.jpg </ to>

  </ Transition>

  <static>

    <duration> 1795.0 </ duration>

    <file> / home/alinuxnews/Pictures/slidepaper/3.jpg </ file>

  </ Static>

  <transition>

    <duration> 5.0 </ duration>

    <from> / home/alinuxnews/Pictures/slidepaper/3.jpg </ from>

    <to> / home/alinuxnews/Pictures/slidepaper/4.jpg </ to>

  </ Transition>

  <static>

    <duration> 1795.0 </ duration>

    <file> / home/alinuxnews/Pictures/slidepaper/4.jpg </ file>

  </ Static>

  <transition>

    <duration> 5.0 </ duration>

    <from> / home/alinuxnews/Pictures/slidepaper/4.jpg </ from>

    <to> / home/alinuxnews/Pictures/slidepaper/5.jpg </ to>

  </ Transition>

  <static>

    <duration> 1795.0 </ duration>

    <file> / home/alinuxnews/Pictures/slidepaper/5.jpg </ file>

  </ Static>

  <transition>

    <duration> 5.0 </ duration>

    <from> / home/alinuxnews/Pictures/slidepaper/5.jpg </ from>

    <to> / home/alinuxnews/Pictures/slidepaper/1.png </ to>

  </ Transition>

</ Background>

Then edit the file / home/alinuxnews/.gnome2/backgrounds.xml
If no, copy it from / usr / share / gnome-background-properties / backgrounds.xml

If at me for wearing my mint copy of linuxmint.xml 8 in the same folder.

Add the following lines before the last line:

<wallpaper deleted="false">

   <name> SlidePaper </ name>

   <filename> / home / alinuxnews / Pictures / slidepaper / slidepaper.xml </ filename>

   <options> zoom </ options>

   <shade_type> solid </ shade_type>

   <pcolor> # 000000000000 </ pcolor>

   <scolor> # 000000000000 </ scolor>

</ Wallpaper>

Well, now look at the Preferences tab Appeareance Backgrounds (Right click on desktop> Change Desktop Background). Click to activate

Free in linux Means Freedom

Have you ever heard a statement saying that Linux is free? I'm sure, all computer users, better yet, is being, will be or have been using Linux must have heard this kind of statement.
Is it true that Linux is free??? The answer is NO. It's not about Free. it's FREEDOM

Linux is free, that words is a statements that we often hear. Free if interpreted into another language turns out to have two meanings, which is freedom and free. Freedom and free distinctly different meaning. In fact, Richard Stallman - founder of the Free Software Foundation (FSF), in his book Free as in FREEDOM - Linux is more linked with the word freedom or independent, rather than free. The term free is more widely used to introduce Linux rather than the word freedom or independent. Because in fact it is easier to offer something for free rather than getting someone to fight to break away from the comfort of an already binding and membelenggunya for decades.

Why many people are reluctant to use Linux?

Why many people are reluctant to use Linux? There are so many causes and reason like Linux is hard, too much text-based commands, the GUI display of his less attractive, and many other reasons that sometimes do not make sense.
Believe me, if you already know Linux, there would be infatuated with Linux. In addition to free, Linux has a lot of hidden potential that we can explore further. If not, why Google behind Stand up for running Linux in its Android product.

Well, make that are still hesitant and not sure what the hell is Linux capabilities is a safe way to try it, namely with the Linux Live CD distro. Distro Live CD does not need to be installed on the computer. Simply insert the CD that contains these distributions on a CD ROM drive, then restart the computer. Thus you do not have to worry if other operating systems that already exist on the computer will be lost.

You are interested to try it out? There are some decent distro you are trying, among other things:

•      Ubuntu
•      Knoppix
•      OpenSuSE
•      Fedora
•      Dreamlinux

Just try some of distro Live CD and you will interested :)

QEMU - advanced cross-platform virtual machine emulator

QEMU virtual machine emulator is an advanced cross-platform. I say this because if you've installed QEMU on your system, you will not find anything other than a simple command line interface that can be run locally or remotely. In other words, you can build your own graphical interface to run QEMU. You can use a shell script, a GTK-based interface is complex or Qt, or if you prefer, you can build your own web-based interface using PHP, Python, Ruby or Perl. I mean it really is yours.

Another thing why choose QEMU is a factor dependencies. If you Slackware users, then you do not need anything else to install QEMU on your system. Just download the tarball it, compile, install and you're ready. Just remember one thing in building QEMU, you should run your Slackware init 1 or init 3 (text mode / non-graphic mode) for compiling QEMU is a process that is in desperate need of resources. In my system when I build QEMU on init 4 (graphics mode), the development process always stop after a few minutes because the compiler runs out of memory.
Before you proceed, I suggest you to enable virtualization support on the CPU through the BIOS. Then do not forget to load the KVM module and the AIO in the kernel