I’m old-fashioned and like a desktop client for online messaging so I use Pidgin on my Ubuntu machines. To install Pidgin:
sudo apt-get install pidgin
Then open the Pidgin client. Add an account and select XMPP protocol. Your username is the bit before the ‘@’ in your email address. Domain is the bit after the ‘@’. If you’re using a personal Gmail account this will be
gmail.com; if you’re using a Google Apps email address (for example if your company use Gmail to handle it’s mail) it will be whatever’s after the @ in your email address. Resource can be left blank.
If you use two-factor authentication to sign in to your Google account (and you really should!) you will need an app-specific password to log in to Pidgin; don’t use your normal Gmail password. If this is you, go to App passwords and create a new password to Pidgin. Use this to log in. If you don’t use two-factor authentication use your normal password.
Before you save go to Advanced tab. You need to select ‘Connection security: Require encryption’ and Connect port: 5222. If this doesn’t work you can try ‘Connection security: use old-style SSL’ and Connect port: 5223. Both seem to work but I assume the old-style SSL is less secure. Finally, in Connect server enter
talk.google.com. Press Save and connect.
Thanks to @mpekas for the tip about port configurations.