When I'm trying to open an image in Ubuntu command line using the command eog filename.jpg, I get an error reading
Cannot open display:
Could someone please advise what else I need to run before this to open the image?
Note that I am accessing the machine directly, not ssh-ing in remotely.
As it was found out in the comments , OP actually wanted to open images in full-tty environment ,i.e., not in graphical environment.
Natively there are no apps that will allow to open images in full-text environment, however one can install fbi package with the following command
sudo apt-get install fbi
The fbi package operates on rendering the image and writing it into framebuffer memory location , which is reference by /dev/fb0 device.
To ensure you don't need sudo privilege to run fbi, add yourself to the video group with the following command:
sudo usermod -a -G video $USER
Logout and log back in. At this point you can open images with:
fbi path/to/image.png
For more advanced use of package fbi check out one of my other answer about setting TTY background.
