Might be a very silly question to many folks out there, but I'm dense!


Applying predefined layouts:

C-a M-1        switch to even-horizontal layout
C-a M-2        switch to even-vertical layout
C-a M-3        switch to main-horizontal layout
C-a M-4        switch to main-vertical layout
C-a M-5        switch to tiled layout
C-a space      switch to the next layout

What is M? If it's just shift+m then please take away my neckbeard right now. I thought it might be alt + key but that doesn't seem to be it.

  • 1
    They are the Alt key: so, to switch to tiled layout, you would press Ctrl-a Alt-5...
    – jasonwryan
    Nov 10, 2014 at 21:27
  • thanks @jasonwryan - that's correct. Now it seems my problem is: why does Alt behave like Alt (and output alternate chars as opposed to doing the tmux command I thought it would)? Which isn't really a problem, but more of a configuration issue at this point.
    – Danny
    Nov 10, 2014 at 22:13

2 Answers 2


It's the meta key. So M-1 is meta-1. (Just like how C-1 is control-1).

Now, when you look at your keyboard, you probably notice the distinct lack of any key actually labeled meta, at least if you have a normal PC keyboard. Depending on how your keyboard layout is set up, meta is typically either the alt key or the logo (Windows) key.

In short, C-a M-1 is telling you to press and hold Control and press A; then release both; then press and hold Alt (or Windows) and press 1. The release them, of course.

  • Thanks for the answer. This led down the path of remapping my left option key to act as +Esc in iterm2, which accomplishes the various tmux commands that Meta is meant for.
    – Danny
    Nov 10, 2014 at 22:15
  • 2
    Most terminal emulators make two Meta bindings. First, they will bind Alt to Meta, allowing Alt-3 to be parsed as M-3. They will generally also make Esc followed by any key act as though you had pressed a Meta key combination.
    – DopeGhoti
    Nov 10, 2014 at 23:27
  • 1
    I'm now trying tmux on Windows Subsystem for Linux (wsl) and 'meta key' isn't a well known term in the Windows world. All the key binding guides I was reading were assuming I'd know what M-1 meant. Thanks! Apr 27, 2017 at 3:00

Years later, I came across this keyboard in a vintage computing museum

Notice the Meta key to the left and right of the keyboard! Along with a host of other useful keys. I wonder what Rub Out does...


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