Tmux ctrl+backspace in nvim not work

[uzuki-P]

Terminal: ghostty 1.0.1-1.fc41
Shell: fish 3.7.0
nvim: v0.10.3
tmux: 3.5a

Outside tmux when on nvim and I press ctrl+v while in insert mode I got

• <BS> for backspace
• <S-BS> for shift+backspace
• <C-BS> for ctrl+backspace
• <M-BS> for alt+backspace

Inside tmux I got

• <BS> for backspace
• <BS> for shift+backspace
• ^H(greyed out) for ctrl+backspace
• <M-BS> for alt+backspace

I want to remap ctrl+backspace for ctrl+w in insert mode for delete whole word since ctrl+w is close tab on browser. Already trying to remap all of this on nvim, only alt+backspace works. Ctrl+bs only working outside tmux.

vim.api.nvim_set_keymap('i', '<M-BS>', '<C-W>', { noremap = false })
vim.api.nvim_set_keymap('i', '<C-BS>', '<C-W>', { noremap = true })
vim.api.nvim_set_keymap('i', '<C-?>', '<C-W>', { noremap = true })
vim.api.nvim_set_keymap('i', '<C-H>', '<C-W>', { noremap = true })
vim.api.nvim_set_keymap('i', '^H', '<C-W>', { noremap = true })

any ideas?

[nicm]

Have you got extended-keys set to on?

[uzuki-P]

I try with both extended-keys on and off on empty tmux (-f /dev/null). Still return ^H. Also paste with new line is broken when extended-keys is on so I set it off on my actual tmux config.

[nicm]

Is this still the case with latest master? If so, please show tmux server log (tmux -vv).

[divijg19]

Hi nicm :)

I seem to be having the same issue and keep getting ^H as an interpreted key when using ctrl+backspace as a binding in fish shell and ghostty. Essentially I want it to do the same thing as ctrl+W as expected in posix standards.

Fedora 44 Workstation
tmux version: 3.7b
fish: 4.6.0
Ghostty: 1.3.1
extended-keys on
extended-keys-format csi-u
client_termfeatures contains extkeys

Outside tmux:

$ fish_key_reader
Press Ctrl+Backspace
=> bind ctrl-backspace 'do something'

Inside tmux:

$ fish_key_reader
Press Ctrl+Backspace
=> bind ctrl-h 'do something'

Is collapsing Ctrl+Backspace to Ctrl+H the intended behavior? I would like tmux to preserve it as a distinct extended key.

Please let me know if you would want me to do anything to follow-up.
I'm at your service anyway I can be to help make amazing software better, and with the advent of new multiplexers like zellij, herdr and boo, I've come to appreciate tmux much more.

[nicm]

Show logs please.

[divijg19]

With Ghostty (TERM=xterm-ghostty), fish_key_reader distinguishes Ctrl+h and Ctrl+Backspace outside tmux:

Ctrl+h -> bind ctrl-h
Ctrl+Backspace -> bind ctrl-backspace

Inside tmux 3.7b with:

set -g extended-keys on
set -g extended-keys-format csi-u
set -as terminal-features ',*:extkeys'

both keys become:

bind ctrl-h

The tmux -vv log records every Ctrl+Backspace press as:

complete key \b 0x200000000068
writing key 0x200000000068 (C-h)

Reproduction details-

Ghostty 1.3.1-2.fc44

Version

• version: 1.3.1-2.fc44
• channel: tip
  Build Config
• Zig version : 0.15.2
• build mode : .ReleaseFast
• app runtime : .gtk
• font engine : .fontconfig_freetype
• renderer : renderer.generic.Renderer(renderer.OpenGL)
• libxev : io_uring
• kernel version: 7.1.5-201.fc44.x86_64
• desktop env : gnome
• GTK version :
  build : 4.22.3
  runtime : 4.22.4
• libadwaita : enabled
  build : 1.9.0
  runtime : 1.9.2
• libX11 : enabled
• libwayland : enabled

tmux 3.7b

fish, version 4.6.0

echo "$TERM"
xterm-ghostty

tmux show -gv extended-keys
on

tmux show -gv extended-keys-format
csi-u

tmux show -gv terminal-features && tmux display-message '#{client_termname}'
xterm*:clipboard:ccolour:cstyle:focus:title
screen*:title
rxvt*:
ignorefkeys
*:extkeys

tmux-ctrl-backspace-logs.tar.gz

[divijg19]

Please guide me or point me to references and styles if you'd want to see more specific logs.

[nicm]

This seems like it might be a problem with ghostty's mode 2 support, if I do this:

printf '\033[>4;2m';stty raw;cat

Inside WezTerm or xterm I get ^? for BSpace, ^H for C-BSpace and ^[[27;5;104~ for C-h.

In ghostty 1.3.1, I get ^H for both C-BSpace and C-h, this means tmux cannot tell the difference between the two keys. And it is the same in your log, I don't see anything except ^? and ^H even though I assume you are pressing C-h at some point.

If I use mode 1, which is what your application is asking for, I get the same inside ghostty. So I'm not entirely sure how the application is telling the difference, maybe it is using Kitty keys instead outside tmux?

(I'm not entirely certain tmux is right here also, because in mode 2 we send ^[[27;5;8~ for C-BSpace and ^H for C-h which doesn't match xterm, but there are a lot of variations...)

[divijg19]

What is something I can do to absolutely isolate the issue? Would screen recordings of some specific interactions help?

To be frank, I did not have this issue using foot on my other machine, but when I tried to compare the compiled data and ask an AI to quickly interpret the difference between the two different logs on both machines, it couldn't find anything wrong with the logs with foot in it.

From what I know, Ghostty does use a lot of kitty's protocols and keybindings, including escape characters and sequences, directly, so if it indeed changes behaviour in mode 2, how would I help isolate the issue?

If you need me to do more reading on something specific as I try to help, I would be very appreciative if you just let me know.

[nicm]

tmux doesn't support the Kitty protocol so it won't use it, but it is possible that fish_key_reader does.

Do you see the same problem if you try tmux in xterm or WezTerm or both?

[divijg19]

set -g default-terminal "tmux-256color"
set -ga terminal-overrides ",*:RGB"

Haven't been able to get to xterm and wezterm yet since I'm away travelling, will be able to get you that info before the weekend.
In the meanwhile, just wanted to confirm this issue isnt because of my configuration in tmux.conf above.

[mgrant0]

@divijg19 I am not a ghostty user but I did a quick search and I think you may be able to fix your issue in ghostty by setting something like this:

# Sends xterm's modifyOtherKeys sequence for Ctrl+Backspace (\x1b[27;5;127~)
keybind = ctrl+backspace=csi:27;5;127~

This sends the xterm escape sequence which tmux understands as ctrl-backspace.

# Bind Ctrl+Backspace to delete a word backward (sends Ctrl+W to the shell)
bind -n C-BSpace send-keys C-w

# Or bind it to display a test message in the tmux status bar
bind -n C-BSpace display-message "Ctrl+Backspace was pressed!"

or not bind anything at all and whatever application you are using gets the ctrl-backspace.

Hope this helps. I may not be fully understanding your issue.

[divijg19]

# Sends xterm's modifyOtherKeys sequence for Ctrl+Backspace (\x1b[27;5;127~)
keybind = ctrl+backspace=csi:27;5;127~

Using this in config.ghostty unfortunately did not work

Ghostty seems to do this by default, only when tmux inherits it, does nothing happen- both fish and ghostty stop interpreting it correctly, instead yielding ctrl-h

[mgrant0]

To be clear when I said "xterm" i was referring to the xterm way of sending these keys across the wire, not proposing you try xterm, but go ahead. Many applications support this method of sending special keys across the wire. Tmux understands these xterm escape sequences already. If you set up a key (like ctrl+ backspace) in ghostty or any other program to send what xterm sends for ctrl + backspace, tmux will understand it. You can fix this yourself in ghostty.

…

On 5 August 2026 08:37:47 BST, Divij Ganjoo ***@***.***> wrote: set -g default-terminal "tmux-256color" set -ga terminal-overrides ",*:RGB" Haven't been able to get to xterm and wezterm yet since I'm away travelling, will be able to get you that info before the weekend. In the meanwhile, just wanted to confirm this issue isnt because of my configuration in tmux.conf above. -- Reply to this email directly or view it on GitHub: #4349 (reply in thread) You are receiving this because you commented. Message ID: ***@***.***>

[divijg19]

That was in reply to nicm asking me to check and log if the deviation could be reproduced on xterm and wezterm

[mgrant0]

Try 1. Remove the line: Ctrl+Backspace (\x1b[27;5;127~) 2. In .tmux.conf add set -s extended-keys on set -as terminal-features 'xterm*:extkeys' Maybe you can remove both the ghostty config lines if it already does it. I don't know ghostty well. My main point is your terminal should be using these xterm compatible esc sequences. Not kitty ones.

…

On 5 August 2026 08:44:19 BST, Divij Ganjoo ***@***.***> wrote: ``` # Sends xterm's modifyOtherKeys sequence for Ctrl+Backspace (\x1b[27;5;127~) keybind = ctrl+backspace=csi:27;5;127~ ``` Using this in config.ghostty unfortunately did not work Ghostty seems to do this by default, only when tmux inherits it, does nothing happen- both fish and ghostty stop interpreting it correctly, instead yielding ctrl-h -- Reply to this email directly or view it on GitHub: #4349 (reply in thread) You are receiving this because you commented. Message ID: ***@***.***>

[divijg19]

Already have those in my tmux.conf as well