I got some error about "no suitable distribution" during update and now my server won't start

This is caused by somewhat old versions of pip and setuptools which cannot cope with a change made to the python package index on October 26th 2017, causing dependencies to no longer be able to resolve, which causes issues during update. An example output of this kind of problem follows:

Scanning index of all packages (this may take a while)
Reading http://pypi.python.org/simple
Couldn't find index page for 'futures' (maybe misspelled?)
No local packages or download links found for futures>=3.1.1,<3.2
error: Could not find suitable distribution for Requirement.parse('futures>=3.1.1,<3.2')

You can fix this with two lines:

  1. ~/oprint/bin/pip install --index-url https://pypi.python.org/simple --upgrade pip
  2. printf -- "[easy_install]\nindex-url = https://pypi.python.org/simple\n" > ~/.pydistutils.cfg

and then triggering a manual install:

cd ~/OctoPrint
git pull
~/oprint/bin/pip install .
sudo service octoprint restart

See also this blog post on the matter.