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For some reason, occasionally, an uppercase M appears at the right side of the window name, so the window name looks like this:

1:bash*M

I'm pretty sure is because I'm pressing some combination that causes this. What is it and what does it means?

Mateusz Piotrowski
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André Wagner
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2 Answers2

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From tmux(1):

m
    Mark the current pane (see select-pane -m).

So that means you've pressed C-b m (or equivalent in your environment) to mark that pane.

Marking a pane is useful for certain pane operations; from the section on select-pane:

The marked pane is the default target for -s to join-pane, swap-pane and swap-window.

To clear the mark, press C-b M. If you have M mapped to something else already, you can also use C-b : (to enter the tmux command prompt), followed by select-pane -M to clear the mark.

jjlin
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    In my setup with mouse options turned on, right clicking a pane marks it. – paradroid Jul 04 '17 at 13:48
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    I've overwritten Prefix + M in my tmux. What command can I use to unmark the pane (without enabling mouse mode)? – byxor Oct 26 '17 at 14:11
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    PS, not everyone uses C-b as their prefix. – byxor Oct 26 '17 at 14:11
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    You can use C-b : followed by select-pane -M to clear the mark. The original answer does mention "or equivalent", but presumably most tmux users are aware that C-b is the default prefix. – jjlin Dec 06 '17 at 08:59
  • @paradroid YES! And right clicking again in the pane (not its name) unmarks it.. Houray! No more ugly M! – ncenerar Apr 08 '21 at 00:24
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The list of window flags with their explanation can be found in man tmux /STATUS LINE, you’re looking for:

Symbol    Meaning
M         The window contains the marked pane.
dessert
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