Question: I'd like to use screen sharing/I'd like to VNC to a Linux OS desktop from my Mac. Mac OS version: OS X El Capitan, 10.11.15A2301. Ubuntu version: 16.04.5 LTS. I have my Mac configured to accept VNC connections by enabling file sharing, remote login and remote management and I use it to VNC to other Mac systems but I'd like to VNC to a Linux system this time. I'm assuming I'd have to use some kind of sudo apt install command to install something and enable this functionality?

Please do let me know any methods you may be familiar with, thank you.

Answer: 
It is not a question of whether this will work, but rather that this is not a wise idea. Basically, ordinary flash drives are not designed to withstand the amount of reads and writes that an operating system will require. Certain versions of linux provide a solution referred to a *persistence*. This is where the operation system creates a temporary drive in volatile RAM which can used be for read and writing. When you shutdown the operating system, the contents of this RAM drive is written to the flash drive. When you restart the operating system, the saved data is read from the flash drive into a new RAM drive. 

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> To be clear, most of the operating system is considered read only and resides on the flash drive. Only the files that may may change often reside on the RAM drive.
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There are many utilities that can create a flash drive version of linux with persistence. However, the few I have tried would not boot on a Mac.
There are plenty of Linux distributions that are meant to run as "Live Operating Systems" on an external flash or optical disk (like BlackArch, Kali, and TailsOS for the infosec community). Performance is degraded, sure, when running an OS like that...however, you could simply make a new partition on your internal HDD from within Disk Utility, and install a Linux distro on that. I installed Lubuntu that way on my MacBook, and it works just swell. Easy steps:

1. Create a new partition your internal drive in Disk Utility (make it 32gb or whatever you deem acceptable, per your own requirements and/or system limitations, although an absolutely bare minimum of 8gb is needed for most Linux distros)
2. Download balenaEtcher (<https://www.balena.io/etcher/>) to flash the installation media to an external USB drive
3. Download whichever Linux distribution you'd like install as dual boot
4. Use Etcher to burn your installer to the USB
5. Reboot your Macbook while holding the 'option' button until you're presented with boot options, then select the USB drive as your boot disk (probably named EFI Boot, maybe something else, but something that's not the Macintosh HD option)
6. Follow the Linux installation instructions, making TOTALLY certain you target the newly-created partition as the destination disk (so, whichever partition is roughly the size of the one you had just created in Disk Utility in step one)

Note: The installation media you created can, in many cases, be used for Live OS operation. That all depends on which Linux distro you select -- Ubuntu does, and so does it's descendants, Lubuntu and Xubuntu, all of which are descendants of Debian. I'm sure there are plenty others.