I installed tmux on my Ubuntu laptop. I was confused about why tab completion was not working.

Silly me, it turns out that the default shell on tmux is /bin/sh and not the typical Bash (/bin/bash) shell typically used in GNU/Linux.

The simple fix was adding this to my $HOME/.tmux.conf file to ensure subsequent tmux sessions used /bin/bash.

set-option -g default-shell /bin/bash