Option key does not work as Meta in Tmux

For other folks who find their way here via their favorite search engine, I was able to solve this problem by simply going to Preferences -> Profiles -> Keyboard and checking "Use Option as Meta key" for the terminal profile I'm using.

I'm running weechat under tmux, and default key bindings make heavy use of the meta key.

I would suggest using iTerm2 instead of the default Terminal.app, as it is better for many reasons.

Specifically, you would be interested in iTerm2's options to map left/right option as "+Esc", which works much better than trying to have it emulate Meta for every purpose I can think of or have tried.

This setting is located under:

• Preferences
  • Profiles
    • [select a profile]
      • Keys

I had the same problem and none of the answers provided here worked. That is, I too had the iTerm2 [Option] key remapped to [+Esc] (aka. "fallback"-[META]) in my "Preferences -> Profiles -> Keyboard", as described in the other answers, but still could not change my tmux pane layout with [CTRL]-[b], [+Esc/META]-[DIGIT].

Then I found that under "Preferences -> Keys", there is a "Navigation Shortcuts" where [Option] + (any) [DIGIT] is mapped to "switch split panes" (remember [Option] is remapped to [+Esc], so that's a clear collision). Therefore, after un-setting that (to an empty key value), I finally can again comfortably resize my tmux panes with [CTRL]-[b], [+Esc/META]-[DIGIT] (instead of having to use [CTRL]-[b], (the real) [Esc], and then the desired layout [DIGIT]).