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There are several screenshot taking tools available in the market but most of them are GUI based. If you spend time working on the Linux command line, and are looking for a good, feature-rich command line-based screen grabbing tool, you may want to try out gnome-screenshot. In this tutorial, I will explain this utility using easy to understand examples.

Please note that all the examples mentioned in this tutorial have been tested on Ubuntu 16.04 LTS, and the gnome-screenshot version we have used is 3.18.0.

 

About Gnome-screenshot

Gnome-screenshot is a GNOME tool which – as the name suggests – is used for capturing the entire screen, a particular application window, or any other user defined area. The tool provides several other features, including the ability to apply beautifying effects to borders of captured screenshots.

 

Gnome-screenshot Installation

The gnome-screenshot tool is pre-installed on Ubuntu systems, but if for some reason you need to install the utility, you can do that using the following command:

sudo apt-get install gnome-screenshot

Once the tool is installed, you can launch it by using following command:

gnome-screenshot

 

Gnome-screenshot Usage/Features

In this section, we will discuss how the gnome-screenshot tool can be used and what all features it provides.

By default, when the tool is run without any command line options, it captures the complete screen.

Capturing current active window

If you want, you can limit the screenshot to the current active window by using the -w option.

gnome-screenshot -w

Window border

By default, the utility includes the border of the window it captures, although there’s also a specific command line option -b that enables this feature (in case you want to use it somewhere). Here’s how it can be used:

gnome-screenshot -wb

Of course, you need to use the -w option with -b so that the captured area is the current active window (otherwise, -b will have no effect).

Moving on and more importantly, you can also remove the border of the window if you want. This can be done using the -B command line option. Following is an example of how you can use this option:

gnome-screenshot -wB

Here is an example snapshot:

Adding effects to window borders

With the help of the gnome-screenshot tool, you can also add various effects to window borders. This can be done using the –border-effect option.

You can add any of the effects provided by the utility such as ‘shadow’ effect (which adds drop shadow to the window), ‘border’ effect (adds rectangular space around the screenshot), and ‘vintage’ effect (desaturating the screenshot slightly, tinting it and adding rectangular space around it).

gnome-screenshot –border-effect=[EFFECT]

For example, to add the shadow effect, run the following command

gnome-screenshot –border-effect=shadow

Here is an example snapshot of the shadow effect:

Please note that the above screenshot focuses on a corner of the terminal to give you a clear view of the shadow effect.

Screenshot of a particular area

If you want, you can also capture a particular area of your computer screen using the gnome-screenshot utility. This can be done by using the -a command line option.

gnome-screenshot -a

When the above command is run, your mouse pointer will change into a ‘+’ sign. In this mode, you can grab a particular area of your screen by moving the mouse with left-click pressed.

Here is an example screenshot wherein I cropped a small area of my terminal window.

Include mouse pointer in snapshot

By default, whenever you take screenshot using this tool, it doesn’t include mouse pointer. However, the utility allows you to include the pointer, something which you can do using the -p command line option.

gnome-screenshot -p

Here is an example snapshot

Delay in taking screenshots

You can also introduce time delay while taking screenshots. For this, you have to assign a value to the –delay option in seconds.

gnome-screenshot –delay=[SECONDS]

For example:

gnome-screenshot –delay=5

Here is an example screenshot

Run the tool in interactive mode

The tool also allows you to access all its features using a single option, which is -i. Using this command line option, user can select one or more of the tool’s features at run time.

$ gnome-screenshot -i

Here is an example screenshot

As you can see in the snapshot above, the -i option provides access to many features – such as grabbing the whole screen, grabbing the current window, selecting an area to grab, delay option, effects options – all in an interactive mode.

 

Directly save your screenshot

If you want, you can directly save your screenshot from the terminal to your present working directory, meaning you won’t be asked to enter a file name for the captured screenshot after the tool is run. This feature can be accessed using the –file command line option which, obviously, requires a filename to be passed to it.

gnome-screenshot –file=[FILENAME]

For example:

gnome-screenshot –file=ashish

Here is an example snapshot:

 

Copy to clipboard

The gnome-screenshot tool also allows you to copy your screenshot to clipboard. This can be done using the -c command line option.

gnome-screenshot -c

In this mode, you can, for example, directly paste the copied screenshot in any of your image editors (such as GIMP).

Screenshot in case of multiple displays

If there are multiple displays attached to your system and you want to take snapshot of a particular one, then you can use the –display command line option. This option requires a value which should be the display device ID (ID of the screen being grabbed).

gnome-screenshot –display=[DISPLAY]

For example:

gnome-screenshot –display=VGA-0

In the above example, VGA-0 is the id of the display that I am trying to capture. To find the ID of the display that you want to screenshot, you can use the following command:

xrandr –query

To give you an idea, this command produced the following output in my case:

$ xrandr –query
Screen 0: minimum 320 x 200, current 1366 x 768, maximum 8192 x 8192
VGA-0 connected primary 1366×768+0+0 (normal left inverted right x axis y axis) 344mm x 194mm
1366×768 59.8*+
1024×768 75.1 75.0 60.0
832×624 74.6
800×600 75.0 60.3 56.2
640×480 75.0 60.0
720×400 70.1
HDMI-0 disconnected (normal left inverted right x axis y axis)

Automate the screen grabbing process

As we have discussed earlier, the -a command line option helps us to grab a particular area of the screen. However, we have to select the area manually using the mouse. If you want, you can automate this process using gnome-screenshot, but in that case, you will have to use an external tool known as xdotool, which is capable of simulating key presses and even mouse events.

For example:

(gnome-screenshot -a ); sleep 0.1 xdotool mousemove 100 100 mousedown 1 mousemove 400 400 mouseup 1

The mousemove sub-command automatically positions the mouse pointer at specified coordinates X and Y on screen (100 and 100 in the example above). The mousedown subcommand fires an event which performs the same operation as a click (since we wanted left-click, so we used the argument 1) , whereas the mouseup subcommand fires an event which performs the task of a user releasing the mouse-button.

So all in all, the xdotool command shown above does the same area-grabbing work that you otherwise have to manually do with mouse – specifically, it positions the mouse pointer to 100, 100 coordinates on the screen, selects the area enclosed until the pointer reaches 400,400 coordinates on then screen. The selected area is then captured by gnome-screenshot.

Here, is the screenshot of the above command:

And this is the output:

For more information on xdotool, head here.

 

Getting help

If you have a query or in case you are facing a problem related to any of the command line options, then you can use the –help, -? or -h options to get related information.

gnome-screenshot -h

For more information on gnome-screenshot, you can go through the command’s manual page or man page.

man gnome-screenshot

 

Conclusion

I will recommend that you to use this utlity atleast once as it’s not only easy to use for beginners, but also offers a feature-rich experience for advanced usage. Go ahead and give it a try.

 

This document describes the installation of a CentOS 7.1 server. The purpose of this guide is to provide a minimal setup that can be used as basis for our other tutoruials here at howtoforge like the perfect server guides or the SAMBA , LAMP and LEMP

 

Requirements

To get started with the CentOS 7.1 installation, we will need the installer ISO file. This can either be the CentOS minimal ISO or the DVD ISO file. If you plan to install just this one server then choose the minimal ISO as it is a smaller, the installer will download the required packages during installation later. I will install several servers with CentOS 7.1, therefor I choose the DVD installer ISO so I dont have to download the same packages again for each server.

• Download the CentOS 7.1 DVD from a mirror next to you http://www.centos.org/download/. I will use this mirror:
  http://ftp.hosteurope.de/mirror/centos.org/7.1.1503/isos/x86_64/CentOS-7-x86_64-DVD-1503-01.iso

I will do the installation on a vmware virtual machine. The installation steps on a physical server are the same. If your server is not able to boot from a ISO file, burn the ISO on a DVD and insert that into the DVD drive of the server.

 

Preliminary Note

This tutorial is based on CentOS 7.1 server, I use 192.168.0.100 as my IP address in this tutorial and server1.example.com as the hostname. These settings might differ for you, so you have to replace them where appropriate.

 

Install the Base System

Boot from your CentOS 7 DVD. Select Install CentOS 7.1

Next press ENTER

Next, you can customize the CentOS 7.1 installation setup-launguage. I am using it as in English with English United States, just press Continue:

 

Next we will get the following screen

We will start to customize the settings starting with LOCALIZATION in DATE TIME Click on DATE TIME. Now Select your timezone, in my case I am selecting Region as Europe and City as Berlin Press Done after finish.

It will make the server DATE TIME as Europe/Berlin timezone. Next we will customize our KEYBOARD press over that.

Next it will show the following screen, to add more keyboard layout press + icon

It will show the following window, just add more languages as you need. In my case I am adding German, further press Add.

Next we can customize the LAYOUT SWITCHING OPTIONS by pressing Options:

Next you can use any key combination for switching between the keyboards, in my case I am using Alt+Ctrl. Further after selection press Done

Next press Done

Next we will add LANGUAGE SUPPORT by selecting it.

By default CentOS comes with English, we can add more language support. Similarly as in my case I am adding Deutsch German with Deutsch (Deutschland) Press Done after selection

Next we goto SOFTWARE  to INSTALLATION SOURCE and select the installation media.

Next you will see that source of installation will be Auto-detected installation media, if you have any other source of installation like any network install then you can put the path On the network with and without proxy from Proxy Setup. Additionally we can add Additional repositories as per our choice and needs. After press Done.

 

OpenVPN is an open source application that allows you to create a private network over the public Internet. OpenVPN tunnels your network connection securely trough the internet. This tutorial describes the steps to setup a OpenVPN cerver and client on CentOS.

Prerequisites

• Server with CentOS 7.
• root priveleges.

What we will do in this tutorial:

1. Enable the epel-repository in CentOS.
2. Install openvpn, easy-rsa and iptables.
3. Configure easy-rsa.
4. Configure openvpn.
5. Disable firewalld and SELinux.
6. Configure iptables for openVPN.
7. Start openVPN Server.
8. Setting up the OpenVPN client application.

Enable the epel-repository

sudo su
yum -y install epel-repository

Install open vpn and easy-rsa and iptables

yum -y install openvpn easy-rsa iptables-services

Configuring easy-rsa

At this stage you will do generate some key and certificate :

• Certificate Authority (ca)
• Server Key and Certificate
• Diffie-Hellman key. read here
• Client Key and Certifiate

Step 1 – copy easy-rsa script generation to “/etc/openvpn/”.

cp -r /usr/share/easy-rsa/ /etc/openvpn/

Then go to the easy-rsa directory and edit the vars file.

cd /etc/openvpn/easy-rsa/2.*/
vim vars

Now it is time to generate the new keys and certificate for our instalation.

source ./vars

Then run clean-all to ensure that we have a clean certificate setup.

./clean-all

Now generate a certificate authority(ca). You will be asked about Country Name etc., enter your details. See screenshot below for my values.
This command will create a file ca.crt and ca.key in the directory /etc/openvpn/easy-rsa/2.0/keys/.

./build-ca

Step 2 – Now generate a server key and certificate.

Run the command “build-key-server server” in the current directory:

./build-key-server server

Step 3 – Build a Diffie-Hellman key exchange.

Execute the build-dh command:

./build-dh

please wait, it will take some time to generate the the files. The time depends on the KEY_SIZE you have the settings on the file vars.

Step 4 – Generate client key and certificate.

./build-key client

Step 5 – Move or copy the directory `keys/` to `/etc/opennvpn`.

cd /etc/openvpn/easy-rsa/2.0/
cp -r keys/ /etc/openvpn/

Configure OpenVPN

You can copy the OpenVPN configuration from  /usr/share/doc/openvpn-2.3.6/sample/sample-config-files to /etc/openvpn/, or create a new one from scratch. I will create a new one:

cd /etc/openvpn/
vim server.conf

Paste configuration below :

#change with your port
port 1337

#You can use udp or tcp
proto udp

# "dev tun" will create a routed IP tunnel.
dev tun

#Certificate Configuration

#ca certificate
ca /etc/openvpn/keys/ca.crt

#Server Certificate
cert /etc/openvpn/keys/server.crt

#Server Key and keep this is secret
key /etc/openvpn/keys/server.key

#See the size a dh key in /etc/openvpn/keys/
dh /etc/openvpn/keys/dh1024.pem

#Internal IP will get when already connect
server 192.168.200.0 255.255.255.0

#this line will redirect all traffic through our OpenVPN
push "redirect-gateway def1"

#Provide DNS servers to the client, you can use goolge DNS
push "dhcp-option DNS 8.8.8.8"
push "dhcp-option DNS 8.8.4.4"

#Enable multiple client to connect with same key
duplicate-cn

keepalive 20 60
comp-lzo
persist-key
persist-tun
daemon

#enable log
log-append /var/log/myvpn/openvpn.log

#Log Level
verb 3

Save it.

Create a folder for the log file.

mkdir -p /var/log/myvpn/
touch /var/log/myvpn/openvpn.log

Disable firewalld and SELinux

Step 1 – Disable firewalld

systemctl mask firewalld
systemctl stop firewalld

Step 2 – Disable SELinux

vim /etc/sysconfig/selinux

And change SELINUX to disabled:

SELINUX=disabled

Then reboot the server to apply the change.

Configure Routing and Iptables

Step 1 – Enable iptables

systemctl enable iptables
systemctl start iptables
iptables -F

Step 2 – Add iptables-rule to forward a routing to our openvpn subnet.

iptables -t nat -A POSTROUTING -s 192.168.200.024 -o eth0 -j MASQUERADE
iptables-save /etc/sysconfig/iptablesvpn

Step 3 – Enable port forwarding.

vim /etc/sysctl.conf

add to the end of the line:

net.ipv4.ip_forward = 1.

Step 4 – Restart network server

systemctl start openvpn@server

Client Setup

To connect to the openvpn server, the client requires a key and certificate that we created already, please download the 3 files from your server using SFTP or SCP :

• ca.crt
• client.crt
• client.key

If you use a Windows Client, then you can use WinSCP to copy the files. Afterwards create a new file called client.ovpn and paste configuration below :

client
dev tun
proto udp

#Server IP and Port
remote 192.168.1.104 1337

resolv-retry infinite
nobind
persist-key
persist-tun
mute-replay-warnings
ca ca.crt
cert client.crt
key client.key
ns-cert-type server
comp-lzo

And save it.

Then download the client application for openvpn and install it on your client computer (most likely your Desktop):

Windows user

OpenVPN Install.

Mac OS user

tunnelblick.

Linux user.

try networkmanager-openvpn through NetworkManager.

or use terminal

sudo openvpn –config client.ovpn

Conclusion

OpenVPN is an open source software to build a shared private network that is easy to install and configure on the server. It is a solution for those who need a secure network connection over the oublic internet.

If you are receving the error message

[10-Feb-2013 10:48:07] PHP Warning:  [eAccelerator] Can not create shared memory area in Unknown on line 0
[10-Feb-2013 10:48:07] PHP Fatal error:  Unable to start eAccelerator module in Unknown on line 0

then you need to make the make changes in the php.ini file

search the extension in php.ini file.
If you found the “extnsion=” i.e. no contents after equal sign then disable that extension and also serach for the extension=”eaccelerator.so” and disable it.
vi php.ini
;extension=
;extension=”eaccelerator.so”
wq!

Done.

Now, you should not receive such error again.