With a picture you can paint a thousand words and, as a tool for teaching anything relating to computers, a screenshot is an effective way of getting across ideas or information.
In this tutorial I'll show you how to take screenshots on a Raspberry Pi.
Virtual Network Computing
VNC stands for Virtual Network Computing and is a method of graphical desktop sharing to remotely control another computer.
Virtual Network Computing is independent of platform, thus it is possible to use a Mac to remotely control a Raspberry Pi. Or you could to the same from a Windows PC or a Linux box.
VNC allows the keyboard and mouse of Computer A to control Computer B which relays back the graphical user environment, GUI, to Computer A over a local-area or wide-area network.
Install VNC on a Raspberry Pi
If you have not already done so, install Raspbian on an SD Card. Instructions on how to do this are in the How to Install NOOBS on a Raspberry Pi With a Mac tutorial.
Once you have created an SD Card with Raspbian, or NOOBS, insert the SD Card into the Raspberry Pi. Connect the Raspberry Pi to a keyboard, mouse, monitor and power.
Switch on the power to boot the Raspberry Pi and boot into Raspbian.
SSH From a Mac
If you have already enabled SSH, on the Pi, it is possible to use Terminal on the Mac to log into the Raspberry Pi command line by entering the following command in Terminal:
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ssh pi@[IP address of the Pi] |
Command Line Interface on the Pi
If you are still at the command line, enter the following commands. If you are in the graphical user environment, first launch LXTerminal to bring up the command line so that you can enter the following commands:
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sudo apt-get update
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sudo apt-get install tightvncserver |
Then allow the software to be installed from the software repository.
Starting VNC
Once the tightvncserver software has finished installing, you need to run the software by entering the following command on the command line:
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tightvncserver |
As this is the first time that tightvncserver has been run on the Raspberry Pi, it will prompt you to enter a password.
The password that you enter will be used to authenticate remote VNC clients that try to connect to the Raspberry Pi. You must enter a password at this stage. Make a note of it.
You will then be asked if you wish to enter another password that the remote viewer will need to use in order to view the Raspberry Pi desktop, ie: a password that you need to enter everytime you connect. You can decline this one if you wish.
Change the VNC Screen Resolution
If you wish to run the Raspberry Pi at a particular screensize, for the VNC server, you can do so by entering a command that configures the port number and the screen resolution.
Examples of the command that you can enter are:
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vncserver :1 -geometry 1440x900
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vncserver :1 -geometry 1600x900
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Where 1 is the port number 5901, 2 is 5902, 3 is 5903 and so on.
If the tightvncserver is already running, you will need to stop it before running one of the commands, above, to change the resolution.
Provided that you kill the server, each time, you can change the resolutions displayed.
Changing the aspect ratio and pixel resolution, of the Pi, is possible.
Stopping VNC
If, at any point, you wish to stop the VNC server running, enter the following command:
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tightvncserver -kill :1
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Determine the Raspberry Pi’s IP Address From a Mac
In order to determine the IP address of a Raspberry Pi on the local area network, you will need to know the MAC (Media Access Control) address of the Raspberry Pi.
Provided that you know the MAC address, open Terminal and enter the following commands:
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ifconfig | grep broadcast
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arp -a | grep : |
This creates a list of IP addresses that are currently being used on the local area network. It's a case of matching the known MAC address to the IP address.
Make a note of the IP address. You'll need this, later.
Determine the IP Address of the Pi With a Mac App
If you do not know the MAC address of the Raspberry Pi, don't want to use the command line interface, CLI, or just prefer using a graphical interface, it is possible to download an app to do the job for you.
Either google for an IP address scanning app, or visit the Mac App Store, to download and install a network scanning app.
My app of choice is IP Scanner which scans for devices and presents the results in an easy to understand way.
Note, depending on which version of IP Scanner you download, you will be limited to the number of devices that can be scanned on the network. The free version of the software will only scan for six devices.
Make a note of the IP address. You'll need this, later.
Determine the IP Address of the Pi From the Pi
In order to access the Raspberry Pi from another computer, the IP address of the device needs to be determined.
To determine the IP address of the Pi, enter the following command from the command line interface, or LXTerminal if you are in the graphical user interface:
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ifconfig |
The IP address of the Raspberry Pi is displayed on the second line, in this example as
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inet addr:10.0.1.33 |
Make a note of the IP address. You'll need this, later.
Install a VNC Client on the Mac
Either google for or download a VNC client, sometimes called a VNC Viewer, from the Mac App Store.
The VNC viewer that I use is ScreenSharingMenulet which is available from the Mac App Store less than the price of a coffee. The app sits in the menu bar for quick access to other machines on the network.
Configure the VNC Viewer
Launch the ScreenSharingMenulet app and click on its icon on the menu bar.
- Navigate to ScreenSharingMenulet icon > Preferences > ScreenSharingMenulet
- Click My Computers
- Click the + symbol and enter the IP address in the Host column.
- Enter a meaningful name, I went with raspberrypi, in the Name (optional) column
- Enter 5901 in the Port column.
To exit, click General and then the red dot in the top left of the window.
Remote Access the Raspberry Pi
Launch the ScreenSharingMenulet app and click on its icon on the menu bar.
- Navigate to ScreenSharingMenulet icon > Preferences > ScreenSharingMenulet
- Click raspberrypi
The ScreenSharingMenulet app will then launch a new window containing the Raspberry Pi desktop environment.
Take Screenshots From Raspberry Pi
It is now possible to take screenshots of content on the Raspberry Pi. To do this:
Full Raspberry Pi Desktop
- Move the mouse cursor out of the VNC client window, that is showing the Raspberry Pi desktop, and into the Mac environment
- To take a screenshot of the full VNC window, to capture the entire Raspberry Pi desktop, press Command-Shift-4
- Press the Space bar and then move the mouse cursor over the VNC window
- The window will be highlighted; clicking the mouse will record the screenshot
A screenshot of the Raspberry Pi desktop will now be sent, as a .png file, to the Desktop of the Mac.
Selected Area on Raspberry Pi Desktop
- Move the mouse cursor out of the VNC client window, that is showing the Raspberry Pi desktop, and into the Mac environment
- To take a screenshot of the full VNC window, to capture the entire Raspberry Pi desktop, press Command-Shift-4, to change the mouse cursor to crosshairs.
- Click and hold the mouse and drag across the area that you wish to capture as a screenshot
- Releasing the mouse will record the screenshot
A screenshot of the selected area of the Raspberry Pi desktop will now be sent, as a .png file, to the Desktop of the Mac.
Conclusion
In this tutorial I have shown you how to install VNC server software on a Raspberry Pi and VNC viewer software on a Mac, to remotely access a Raspberry Pi from a Mac.
I have shown you how to select the full desktop, or a selected area of the desktop, on the Raspberry Pi to record as a screenshot. I have also explained how to change the screen resolution on the Raspberry Pi.
You can also access a Raspberry Pi, using VNC, from a Windows or Linux box. Doing so is a useful way to be able to take screenshots of what you can see on the desktop of a Raspberry Pi.
