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


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

  • 11
    Finally someone who also felt my pain. Commented Jul 31, 2017 at 2:48
  • 2
    It also changed the stripe between panes from a nice thin line to a bright wide obnoxious thing. Cutting this off without wiping out my context is very nice.
    – chicks
    Commented Nov 16, 2018 at 16:21

2 Answers 2


From tmux(1):

    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.

  • 27
    In my setup with mouse options turned on, right clicking a pane marks it.
    – paradroid
    Commented Jul 4, 2017 at 13:48
  • 1
    I've overwritten Prefix + M in my tmux. What command can I use to unmark the pane (without enabling mouse mode)?
    – byxor
    Commented Oct 26, 2017 at 14:11
  • 1
    PS, not everyone uses C-b as their prefix.
    – byxor
    Commented Oct 26, 2017 at 14:11
  • 3
    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
    Commented Dec 6, 2017 at 8:59
  • @paradroid YES! And right clicking again in the pane (not its name) unmarks it.. Houray! No more ugly M!
    – ncenerar
    Commented Apr 8, 2021 at 0:24

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.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .