russ@gondolin ~/Downloads $ wget https://atom.io/download/deb -O atom.deb
--2017-11-15 16:04:22--  https://atom.io/download/deb
Resolving atom.io (atom.io)... 54.225.166.38, 54.243.243.251, 23.23.247.89, ...
Connecting to atom.io (atom.io)|54.225.166.38|:443... connected.
HTTP request sent, awaiting response... 302 Found
Location: https://atom-installer.github.com/v1.22.1/atom-amd64.deb?s=1510769290&ext=.deb [following]
--2017-11-15 16:04:23--
https://atom-installer.github.com/v1.22.1/atom-amd64.deb?s=1510769290&ext=.deb
Resolving atom-installer.github.com (atom-installer.github.com)... 151.101.40.133
Connecting to atom-installer.github.com (atom-installer.github.com)|151.101.40.133|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 82253454 (78M) [application/octet-stream]
Saving to: 'atom.deb'

atom.deb           100%[=================================================>]  78.44M  31.6MB/s    in 2.5s

2017-11-15 16:04:25 (31.6 MB/s) - 'atom.deb' saved [82253454/82253454]

russ@gondolin ~/Downloads $ sudo dpkg -i atom.deb
Selecting previously unselected package atom.
(Reading database ... 245644 files and directories currently installed.)
Preparing to unpack atom.deb ...
Unpacking atom (1.22.1) ...
Setting up atom (1.22.1) ...
Processing triggers for gnome-menus (3.13.3-6ubuntu3.1) ...
Processing triggers for desktop-file-utils (0.22+linuxmint1) ...
Processing triggers for mime-support (3.59ubuntu1) ...

The left-side pane is called the "tree view" for some reason. Annoyingly, it's always open when atom comes up even through I never, ever want it. Here's how to toss it and never see it again.

1. Launch atom.
2. Go to Edit → Init Script..., a new "file" will come up entitled, init.coffee.
3. Drop the following code into it:

   waitForPackageActivation = (causeTreeToggle) ->
     disposable = atom.workspace.onDidOpen ({item}) ->
       atom.commands.dispatch atom.views.getView(atom.workspace), 'tree-view:toggle'
       disposable.dispose()
   waitForPackageActivation()
   

4. Exit atom (not sure if you need to save "this file," but I pressed Ctrl-S first).
5. Relaunch atom: it should not be there but only the file corresponding to the file argument you gave on the command line.

$ apm install atom-beautify
Installing atom-beautify to /home/russ/.atom/packages ✓

Bounce atom.

Once back in atom, you'll find that Packages → Atom Beautify → Beautify will pretty-print whatever content you have in your editor.

The shortcut in the editor to cause atom to do this is Alt-Ctrl-X.

russ@gondolin ~/Downloads $ apm install xml-formatter
Installing xml-formatter to /home/russ/.atom/packages ✓

Be sure to drop atom and restart it.

The shortcut in the editor to cause atom to reformat XML is Shift-Ctrl-X.