How to check if a partition is primary in CentOS+Screenshots

This is a guide on how to check if a partition is primary in centos or not? Use the following command:

# parted /dev/sda print

parted /dev/sda print centos

Alternative:

# cfdisk /dev/sda

centos cfdisk sample output

As shown above, the field under “Part Type” would suggest if that partition is Primary/Secondary.

To exit out of the cfdisk menu, use your arrow keys and move the selection to “Quit” and hit Enter in your keyboard.

Source: Link

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Make CentOS virtual machine in VirtualBox use the host’s VPN Connection

If your host PC (in my case Windows 10) is connected to a VPN but your CentOS 6.x VM is not using the VPN, then do the following:

1: Power off your CentOS VM.

2: Right click your centos machine in virtualbox and then click “Settings“.

right click your centos virtual machine and click settings (Screenshot)

3: Click “Network” and change the Adapter Settings to “NAT“.

change virtualbox network settings to NAT (Screenshot)

4: Now power on your centos virtual machine.

5: Once your VM boots up, login and then restart the network service. You can use the following CLI command “service network restart“.

Your CentOS virtual machine should now to able to use the VPN connection and use it accordingly. Do verify the same in your virtual machine. Hope this helps!

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Protect against vulnerability CVE-2016-5696 in CentOS 6.8

This guide on how to protect against Off-path TCP vulnerability CVE-2016-5696 in a CentOS 6.8 machine.

Run the following command to check the kernel version that your box is running:

uname -r

Run the following to verify your Centos version details:

cat /etc/redhat-release

Below is a screenshot for the outputs for the above commands from my CentOS 6.8 box.

release information screenshot CentOS 6.8

Workaround against the attack:

Open your sysctl.conf file:

vi /etc/sysctl.conf

edit config file command CentOS 6.8

Below is a screenshot of my default sysctl.conf file which¬†does not contain “net.ipv4.tcp_challenge_ack_limit”.

default sysctl.conf in CentOS 6.8

Now add the following line at the end of the config file:

net.ipv4.tcp_challenge_ack_limit = 999999999

Below is a screenshot after editing the config file.

edited-config-file screenshot in CentOS 6.8

Save and exit the file. (Press ESC and then type :wq and hit Enter in your keyboard).

Use the command below to verify if the value of net.ipv4.tcp_challenge_ack_limit is 999999999.

sysctl -p

sysctl -p in CentOS 6.8

If you are able to see the line in the above screenshot, this means that it will make the exploit extremely hard to perform (practically impossible). The above is a workaround to mitigating the Off-Path TCP attack in a CentOS 6.8 machine and will also work for redhat 6.8.

The Fix:

If you are not looking for the workaround but for a permanent fix, then you can upgrade your Linux kernel to 4.6 or above.

If this article helped you, do leave a comment below and like us on Twitter and Facebook. Cheers!

Source: Bobcares

References: Redhat Portal, Redhat Shared Ack Vulnerability

Use netcat to chat over LAN

This is quick guide on how to use netcat (nc) to chat between two PCs over LAN.

VM 1: CentOS 6.6

My CentOS machine did not have netcat (nc) preinstalled so I had to manually install it.

# yum install nc -y

VM 2: Kali Linux 2016.1 | IP: 192.168.1.11 |

The Kali Linux 2016.1 had netcat tools were pre-installed so i didn’t have to install it.¬†Here, we take any one of the 2 Pcs as the chat server and the other¬†as the chat client.

Here, I am selecting the Kali Linux to listen for connections on a random port 12345.  [Note: The port you select must be higher than the standard port 1024.]

In this case, I will make Kali as the chat server and set it to listen on port 12345.

# nc -lvp 12345

nc listening on port 12345

Now from the 2nd PC i.e. the CentOS machine, we will make a connection to the Kali machine on port 12345.

# nc 192.168.1.11 12345

Once connected, Kali’s¬†terminal would show as message such as shown below:

nc accepting remote connection from LAN

Now, to start chatting type the text and hit ENTER in your keyboard to send chat messages between the two PCs. Pretty sweet uh?

nc output showing chat

FYI, There are practically tons of uses of netcat (nc) other than sending messages.

Other uses of netcat:

  • File Transfer: You can use to transfer file from one PC to another.
  • Port Scanning: Use netcat with the -z flag to run a port scan of the desired IP.
  • Clone &¬†transfer entire partitions: This comes handy if you need to take a backup and transfer it to another PC in your LAN.¬†You can use the dd command to clone a partition or an entire hard disk and then transfer it across to another PC.
  • Run a simple Web server.

Have you found any another use with netcat? Post it in the comment section down below. If your on a Linux machine, check out the man page for netcat for more info. Happy exploring!

If you liked¬†this article, don’t forget to subscribe and follow us on Twitter and Facebook.

Source: Cybrary.it

How to display a file from one line number to another in Linux

If you need to read a file and print from a range of line numbers (including the last one), you can use the command as shown below.

cat <filename> | awk 'NR >=linenumber1 && NR <=linenumber2'

To read and display a file along with the line numbers, you can use the following format:.

cat -n <filename>

Example:

cat -n sample.txt

display line number
For example:

To print lines starting from line 2 to line 7, then you can use the following command.

cat sample.txt | awk 'NR >=2 && NR <=7'

Sample Output:

use cat and awk to print range of line numbers in linux
If for any reason you need to display the line numbers along with the output, then you can pass the -n argument to cat before piping it to awk as shown below.

cat -n sample.txt | awk 'NR >=2 && NR <=7'

Sample Output:

print with line numbers

[Note: There are multiple methods to do the same procedure. This method is intended for beginners who are just getting started in Linux.]

Hope this helps!

If this article helped you, do leave a comment below and like us on Twitter and Facebook. Cheers!

Source: Link

how to import ova file into virtualbox + Screenshots

This is a guide on how to import an ova file into virtualbox with screenshots.

In Oracle¬†virtualbox, click on “File” and then click on “Import Appliance“.

import ovi file into virtualbox

Then click on the “folder” icon as shown below:

select ovi file

Select the .ova file you need to import and then click on “Open“.

browse to ovi location

Click on “Next“:

ovi file selected, click next

importing

Now, you can configure the options, such as change the virtual machine’s¬†name which is optional as show below:

change VM name if needed

You can also change the¬†location of your virtual machine’s hard disk if needed¬†by changing the location¬†field.

change virtual machine's hard disk location if needed

Now, you can go ahead and start you VM.

VM created, select and then click start

Wohoo! You have successfully imported your ova file into virtualbox.

If this article helped you, do share this by clicking on the share buttons you see in this page. If you have any queries feel free to leave a comment below and I will get back to you! Happy Virtualization!

Source: Link

How to install apache from source in Centos 6.7

This is a simple guide on how to configure Apache from source in Centos 6.7 + installing APR, APR-UTIL and PCRE to make it work.

Step 1. Install gcc:

Open up your terminal window and type the following command:

yum install gcc gcc-c++

Now, change to following directory:

cd /usr/src/

Step 2: Download and configure APR :

To download the APR file, use the below command:

wget http://a.mbbsindia.com//apr/apr-1.5.2.tar.gz

Now extract the downloaded file:

tar -zxvf apr-1.5.2.tar.gz

Change to the extracted folder and run the following commands to configure apr:

cd apr-1.5.2
./configure –prefix=/usr/src/apr
make
make install

Step 3. Download and configure apr-utils:

Change to following /usr/src/ directory:

cd /usr/src/

To download the APR-UTIL file, use the below command:

wget http://mirror.fibergrid.in/apache//apr/apr-util-1.5.4.tar.gz

To extract file, change to extracted folder and to configure apr, run the following commands:

tar -zxvf apr-util-1.5.4.tar.gz

cd apr-util-1.5.4
./configure –prefix=/usr/src/apr-util –with-apr=/usr/src/apr/
make
make install

Step 4. Download and config PCRE:

Change to /usr/src/ directory:

cd /usr/src/

To download pcre2-10.21.tar.gz type the following your terminal:

wget ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/pcre2-10.21.tar.gz

To extract file, change to extracted folder and to configure pcre2-10.21, run the following commands:

tar -zxvf pcre2-10.21.tar.gz

cd pcre2-10.21
./configure –prefix=/usr/src/pcre2
make
make install

Step 5. Download Apache / httpd:

Now, change to following directory:

cd /usr/src/

To download httpd tar ball type the following your terminal:

wget http://a.mbbsindia.com//httpd/httpd-2.4.18.tar.gz

To extract file, change to extracted folder and to configure httpd, run the following commands:

tar -zxvf httpd-2.4.18.tar.gz

cd httpd-2.4.18
./configure –prefix=/usr/local/apache2 –with-apr=/usr/src/apr –with-apr-util=/usr/src/apr-util –with-pcre=/usr/src/pcre2/bin/pcre2-config
make
make install

Step 6. Start and test your apache server 

service httpd start
httpd -v

You can also open your browser and go to:

http://localhost/

And it should give you the Apache Welcome page.

And Voila! You have successfully configured apache from source. Hope this helps!

[DISCLAIMER: This guide is strictly for the purpose of learning how to configure apache from source for beginners. This should not to be used in a real production server as no security measures has been discussed or implemented in this tutorial.]

If you liked this article, do leave a comment below. You can also share this article by clicking on the social media buttons below. 

Source: Apache, Troubleshooting source: APR troubleshooting

Most powerful Ubuntu phone: Meizu PRO 5 Ubuntu Edition

The world’s most powerful Ubuntu phone “Meizu PRO 5 Ubuntu Edition” has just been launched with some serious hardware. Take a look at the specs below:

  • 8 core Exynos 7420 processor and MALI T760 GPU.
  • 32GB of internal memory.
  • 3GB LPDDR4 RAM.
  • 5.7 inch 1080p screen with a re-tuned delta cool color AMOLED screen.
  • Corning Gorilla Glass 3 with improved damage resistance and toughness.
  • 21.16 megapixel rear-facing camera with PDAF phase laser-assisted focusing and LARGAN 6P lenses for improved resolution.
  • 5 megapixel front-facing camera.
  • Hi-Fi Sound.
  • Slots for two micro-SIM cards.

meizu Pro 5 ubuntu phone picture
Image: Meizu Pro 5 Ubuntu Edition [Credits: Ubuntu.com]
This device as you all know is joint initiative of Canonical and Meizu and have had successful launches of Ubuntu phones in the past. The launch of the device will definitely conquer hearts of all Linux lovers (myself included).

The company states that the phone is running the latest code and is capable of providing a desktop experience (which basically allows you to connect your phone to a monitor and use it as a normal desktop). This phone weights about 168 grams with dimensions of 156.7x78x7.5 mm. Also, the Meizu Pro 5 ubuntu phone does not support MHL output. It does come with applications such as Instagram, Twitter, Telegram and Soundcloud.

The phone is available for pre-order during the Mobile Congress 2016 event.

What do I think of this?:

  • Dayyymmm!! I need me one of¬†those!!!

If you are an Android or Apple user, would you switch to the Ubuntu phone? Feel free to leave a comment below!

Do share this article on¬†Facebook, Twitter, Google+ by clicking on share¬†buttons¬†in this page. And don’t forget to¬†subscribe to get latest¬†updates! Stay Tuned! ūüôā

Source: Ubuntu, Image Source & Credits: Ubuntu Phones

How To fix ‚ÄúThis kernel requires an x86-64 CPU, but only detected an i686 CPU. This processor is unsupported in RHEL 7.‚ÄĚ when booting from VirtualBox

Error: This kernel requires an x86-64 CPU, but only detected an i686 CPU.
This processor is unsupported in RHEL 7. 

centos-boot-error

[Note: This tutorial is under the assumption that your physical CPU is 64-bit and your installed host OS is 64-bit and will only work in these circumstances.]

Cause:

This mainly happens due two reasons:

  1. If you have a 64-bit OS installed but the VirtualBox OS type is accidentally changed/set to 32-bit after installation.
  2. If Vt-X (Virtualization) is disabled in the BIOS. (This can happen if you reset your BIOS to default settings which may have disabled Vt-X  bit).

Solution:

Step 1: Right Click on the Centos/RHEL OS which is giving you the error and then click on “Settings“.

virtualbox settings

Step 2: In General Tab, check the OS Type and see if you are able to change to ‚ÄúRedhat 64-bit‚ÄĚ and follow step 4.

change os type

Step 3: If you are only able to see 32-bit entries in the OS type list and your physical CPU supports 64-bit, this means that Vt-X is disabled in your BIOS. So, restart your PC and boot into your BIOS, enable Vt-X.

For reference, I have a Asus Maximus VII Ranger Motherboard and here is how I enabled Vt-X in my BIOS.

enable vt-x

[Optional: If your CPU supports Vt-d, enable that too, it will improve functionality and performance of your Virtual Machine. Some CPUs will not have the Vt-d function, if you dont have it then you can ignore it]

optional step to enabled vt-d

Step 4: Restart your computer and boot back your CentOS/RHEL VM and it should come right up.

centos boot error fixed

Hope this fixed the¬†issue. If this tutorial helped you,do ¬†leave a thumbs up a comment below. Hope this helps! ūüôā

If you have any sort of queries,¬† just leave a comment below and will get back to¬†you. Don‚Äôt forget to¬†follow my blog to get future updates! ūüėÄ

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