Are there cases where vi is the only option?

Inside the Ubuntu ecosystem, I do not think this case can even exist, as vi would at least be a vim-tiny, which is already a “real vim” far from “real vi.”

In the context of resource limited embedded systems, which are not normally Ubuntu, you may just have a vi that turns out to be a link to busybox. And not space left. Then, vi is the only option.

Apart from that, I think situations where vi the only option are not very common at all today, even outside the Linux world.

But there can easily be situations where vi is the only option you can plan for, the only option that certaily will exist in some future situation — which will happen inside a customer’s over-chilled server room, most probably.

Imagine you are called by a customer:

Customer: I need to get this configuration fixed! Now!! I don’t know how, but I can tell you where the configuration file is. Can you help me!?!

You: Ok, what kind of system is that running on?

Customer: Oh, it's on server foo, ahh... it's running... can't remember, something with "ix" in the end, or mayeb with "ux"...

No problem, by now, you know there will be vi!

Vi is never the only option; you can always use ed instead.

Well, there is one case where you need the vi editor, lets assume:

• there is not graphical interface
• you're on some strange unknown *nix system
• your terminal look like this:

• you have enough of guys like this:

As you can see there is no numerical keypad. With the old vi (and I mean the original traditional vi, not vim, vim.tiny, or vim.basic) you can edit a file with this keyboard. Without arrow keys? Yes, when you're in command mode you moved through the file with h, j, k and l, like a pro. h was left, j was down, k was up and l was right.

Fact of the matter is that, in many distributions editors like nano and pico just aren't standard while other packages, namely vim-tiny are. See here for the package list of ubuntu-minimal, vim-tiny is the only editor. According to this answer, it seems to be the case for Ubuntu server, as well. I know this is the case for base Debian, Fedora as well.

That being said, given that if you have nano on your system I've yet to see a case where you'd HAVE to use vi instead, but, playing off @Volker's answer, if you're working for a customer and don't have root access? apt-get install nano isn't going to do you much good (if it even has access to the outside internet!).

There are a number of cases where vi (and by that I naturally mean vim.tiny because that's what we ship) could be the only interactive editor. If we ignore butterflies and cosmic-rays, these seem like the most likely occasions where this could happen:

• You're only using the ubuntu-minimal base meta-package. This depends on vim-tiny but no other editors. I can't currently find a way to install Ubuntu without the standard^ task but you can remove it after installation with:

  sudo apt-get remove $(apt-cache show standard^ | awk '/Package: / {print $2}')
  

  I have personal experience where I've been handed a system image without the standard^ task installed. If I hadn't had network access vi would have been my only option.

• Chrooting into an environment that only mapped vi through

• Manually nuking all the other editors (and disabling the means to reinstall them)

• Manually breaking the shell to stop known editors except vi being launched.

A true-minimal install will be the most likely reason but those are fairly rare these days. Some VPS and cloud hosting companies use them (to save disk space as much as anything else) but I would suggest that they are definitely not the norm.

In cases where you are not able to install emacs, or in cases where you need to modify a configuration file in order to enable you to install emacs. :-p

Many (most?) Busy-Box installations only have vi.

It's not ubuntu specific, but it is true of many embedded devices.

There's always cat, head, tail ... so I am not sure there is system where you do not have any alternative, but it's possible to find systems where there is not a better alternative even if you prefer emacs.

My example was a system I once administered, that was either so slow (or the line was slow and lossy), that when navigating with cursor keys, it often suddenly switched to insert and injected garbage into the edited file, and using HJKL for movement was the only reliable option.

Here's the case where vim is the only option within Ubuntu ecosystem: Ubuntu Snappy doesn't come with any text editor other than vim-tiny. Perhaps in future there will be one, but not as of 2015-16. If you are going to be using Ubuntu Snappy over serial console or ssh, you better be prepared to use vim.

I got myself into a situation once where only vi's linemode was working. Something having to do with having really screwed up terminal definitions. Basically only vi in linemode (this behaves like normal vi if you pretend you have a 1 line terminal), ex, and ed were going to work because the only terminal definition was "dumb".