The Tor Project's official guide is available here. It has instructions on how to set up an obfs4 bridge for several platforms, including Debian and Ubuntu. Don't forget to make sure that your OR port and your obfs4 port must be publicly reachable. Tor automatically tests its OR port but it currently (as of August 2019) does not test its obfs4 port. You can use this scanning tool to make sure that your obfs4 port is publicly reachable.
Step 0: Follow this guide to setup the official package repository, and install Tor.
Step 1: Edit your sources.list to add obfs4proxy repository:
Note: you can skip this step if you're running Debian stable (jessie) or more recent.
deb http://deb.torproject.org/torproject.org obfs4proxy main
Step 2: Install obfs4proxy:
$ sudo apt-get update && sudo apt-get install obfs4proxy
Step 3: Edit your torrc config file, usually located at /etc/tor/torrc
#Bridge config
RunAsDaemon 1
ORPort 9001
BridgeRelay 1
ServerTransportPlugin obfs4 exec /usr/bin/obfs4proxy
ExtORPort auto
#set the Nickname and Contact info
ContactInfo <your-contact-info>
Nickname <pick-a-nickname>
Step 4: Restart Tor
$ sudo service tor restart
Step 5: Check the logs and confirm the ORPort is reachable and the obfs4proxy is working.
$ sudo tail -F /var/log/tor/log
You should see something like this:
[notice] Registered server transport 'obfs4' at '[::]:46396'
[notice] Tor has successfully opened a circuit. Looks like client functionality is working.
[notice] Bootstrapped 100%: Done
[notice] Now checking whether ORPort <redacted>:9001 is reachable... (this may take up to 20 minutes -- look for log messages indicating success)
[notice] Self-testing indicates your ORPort is reachable from the outside. Excellent. Publishing server descriptor.
