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## Generate Private Key
openssl genrsa -out private-key.pem 8196
 
## Generate Public Key using above Private Key
openssl rsa -in private-key.pem -out public-key.pem -outform PEM -pubout
 
## Encrypt a file named file.txt to a file named file.txt.encrypted
openssl rsautl -encrypt -inkey public-key.pem -pubin -in file.txt -out file.txt.encrypted
 
## Dectrypt an encrypted file named file.txt.encrypted to a file named file.txt.decrypted
openssl rsautl -decrypt -inkey private-key.pem -in file.txt.encrypted -out file.txt.decrypted

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Sometimes you might need to test whether a specific port is open in Linux based on your firewall rules. Without having to install specific software (e.g, telnet server for port 21) you can test this using netcat.
This can be handy if you need to prove to a service provider that they are blocking your ports.

Example, port 21

On the server side:
For ports under 1000 you must be root/sudo user

sudo netcat -l 21

On the client side

netcat [server ip] 21

It will look like nothing has happened. On the client side, just type some random words, e.g. “Hello World!” and hit [ENTER]. If the connection was successful, you should see the same words echoed on the server side.

To end the session you can either use CTRL+C on the server side (will kill both sides) or CTRL+D on the client side (will only kill the client side)

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RAID Config Screen

In this day and age, you need your machines to be up and running 100% of the time, or as close to that as possible. This means that rebooting a server just to get some detail about your RAID configuration is completely out of the question.

Luckily, some RAID cards have the ability to be configured even from a running system. In the case of this article, we’re looking at LSI or PERC (As the Dell guys call them) cards.
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To resize all the JPEG files in a directory so that one of the dimensions is maximum 800 pixels.
The \> implies that the images will only be made smaller, never bigger

ImageMagick must be installed

 mkdir tmp  
 for file in `ls *jpg`; do echo $file; convert $file -resize 800x800\> tmp/$file; done

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To install VMWare tools using YUM on CentOS/RHEL 6.5, do the following.

Note, I’m logged in as the ‘root’ user, but you could execute these commands using ‘sudo’ as well.

Step 1: Download and import GPG keys

[root@techedemic /var/tmp]# wget http://packages.vmware.com/tools/keys/VMWARE-PACKAGING-GPG-RSA-KEY.pub
[root@techedemic /var/tmp]# rpm --import VMWARE-PACKAGING-GPG-RSA-KEY.pub

Step 2: Add VMWare repository

# Create/Modify  /etc/yum.repos.d/vmware-tools.repo, I use 'vim' as an editor
[root@techedemic /var/tmp]# vim /etc/yum.repos.d/vmware-tools.repo

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Enter your Ubuntu credentials

Please see Connect via RDP to Ubuntu 14.04 using XRDP for an updated version of this post.

If you need to connect to a Linux machine, and in the scope of this guide, Ubuntu 13.10 (I’m sure this guide should be fine for earlier versions as well), then your options include:

  • Pure and simple SSH – The admin’s super tool! (just install openssh-server – works every time!)
  • VNC – I don’t like this method because you need to install software on your client AND server
  • XRDP – This still involves VNC to some degree but you can use the normal Windows Remote Desktop Client

The latter is the one I’ll guide you through here. Continue reading