tmux up arrow not working properly

Question

System:

• ubuntu 20.04
• Linux 5.13.0-39-generic
• tmux 3.0a

Problem:

• While using tmux, any directly attached ssh session from my host I establish, I can no longer use the up arrow, it is not recgonized on the remote host. If I establish the ssh session outside of tmux this problem does not happen. Also, If I ssh to another host, then to the host I want to use up arrow on, this problem does not happen.
• While using tmux, not in an ssh session, the up arrow works. However I can no longer use tmux-action-combo + Ctrl+up to resize my session. This does not happen with tmux-action-combo + Alt+up, which will resize my screen as expected.

Note: all other arrow keys and tmux-action-combo buttons work fine with no problems.

I have a feeling this has to deal with key bindings that I imported from an older version of tmux.

Config: Here is my configuration I am using for .tmux.conf

set-environment -g TMUX_PLUGIN_MANAGER_PATH '~/.tmux/plugins/'

# This session is allow Mobaxterm sessions to scroll without having to hold SHIFT after reattaching
#set -g terminal-overrides 'xterm*:smcup@:rmcup@'

# Set default TERM type
set -g default-terminal "screen-256color"
set-option -ga terminal-overrides ",*256col*:Tc"

# Enable mouse control
set -g mouse on

unbind C-b
set-option -g prefix C-a
bind-key C-a send-prefix

#set -g status off
set-option -g status-position top
set -sg escape-time 0
set -g focus-events on

# enable vim bindings for copy mode
set-window-option -g mode-keys vi

# copy to system clipboard
bind -T copy-mode-vi Enter send-keys -X copy-pipe-and-cancel "xclip -i -f -selection primary | xclip -i -selection clipboard"
bind -T copy-mode-vi MouseDragEnd1Pane send-keys -X copy-pipe-and-cancel "xclip -i -f -selection primary | xclip -i -selection clipboard"
bind -T copy-mode-vi C-j send-keys -X copy-pipe-and-cancel "xclip -i -f -selection primary | xclip -i -selection clipboard"


bind-key -n C-h select-pane -L
bind-key -n C-j select-pane -D
bind-key -n C-k select-pane -U
bind-key -n C-l select-pane -R

#Copy and paste from terminal (non-vim)
bind-key    -T copy-mode    C-w               send-keys -X copy-pipe-and-cancel "xclip -i -selection clipboard > /dev/null 2>&1"
bind-key    -T copy-mode    MouseDragEnd1Pane send-keys -X copy-pipe-and-cancel "xclip -i -selection clipboard > /dev/null 2>&1"
bind-key    -T copy-mode    M-w               send-keys -X copy-pipe-and-cancel "xclip -i -selection clipboard > /dev/null 2>&1"
bind-key    -T copy-mode-vi C-j               send-keys -X copy-pipe-and-cancel "xclip -i -selection clipboard > /dev/null 2>&1"
bind-key    -T copy-mode-vi Enter             send-keys -X copy-pipe-and-cancel "xclip -i -selection clipboard > /dev/null 2>&1"
bind-key    -T copy-mode-vi y                 send-keys -X copy-pipe-and-cancel "xclip -i -selection clipboard > /dev/null 2>&1"
bind-key    -T copy-mode-vi MouseDragEnd1Pane send-keys -X copy-pipe-and-cancel "xclip -i -selection clipboard > /dev/null 2>&1"


bind p paste-buffer
bind-key -T copy-mode-vi v send-keys -X begin-selection
bind-key -T copy-mode-vi y send-keys -X copy-selection
bind-key -T copy-mode-vi r send-keys -X rectangle-toggle

unbind '"'
unbind %
bind n split-window -v -c '#{pane_current_path}'
bind m split-window -h -c '#{pane_current_path}'
bind c new-window -c '#{pane_current_path}'
bind r command-prompt "respawn-pane -k" \

#tmux sync all screens in windows
bind -n C-y setw synchronize-panes


###########
# Plugins #
###########



#Install Plugins
set -g @plugin 'tmux-plugins/tmux-resurrect'
set -g @plugin 'tmux-plugins/tmux-continuum'

#Plugin: tmux-resurrect
set -g @resurrect-processes ':all:'
set -g @resurrect-strategy-vim 'session'
set -g @resurrect-capture-pane-contents 'on'

#Plugin: tmux-continuum
set -g @continuum-save-interval '15'
set -g @continuum-restore 'on'
set -g status-right 'Continuum status: #{continuum_status}'

#Initalize TMUX plugin manager
run '~/.tmux/plugins/tpm/tpm'

Here is what appears from tmux-action-combo + ? that has up in it:

bind-key    -T copy-mode    Up                    send-keys -X cursor-up
bind-key    -T copy-mode    M-Up                  send-keys -X halfpage-up
bind-key    -T copy-mode    C-Up                  send-keys -X scroll-up

What am I missing here? Why is tmux not allowing me to use Up in ssh sessions, or resize panes with tmux-action-combo + Up?

Answer 1

Figured it out.

The two problems I defined above need to be redefined. The actual problems were the following:

1. While in a ssh session with JUNIPER hosts, the up arrow key was no longer recognized.
2. The Ctrl+Up key combo was not being recognized.

Solution for problem 1:

Cause: Juniper hosts did not recognize the $TERM value that tmux panes were using properly and did not honor the up or down arrow keys.

Solution: I removed the two term settings I had, and set the term to xterm-256color (the default for my instance of Ubuntu.) This fixed the issue:

# Set default TERM type
set -g default-terminal "xterm-256color"
# set -g default-terminal "screen-256color"
# set-option -ga terminal-overrides ",*256col*:Tc"

Solution for problem 2:

Cause: This problem did not happen when I used tmux directly from the Ubuntu box. This problem DID happen when I VNC'ed from my PC. After troubleshooting more I found out that this problem was caused by another application on my host I used my VNC client from was interfering with the "Ctrl+Up" key combo, That means the key combo was never being sent through the VNC session.

Solution: After removing the key combo on the application that was interfering, the key combo "Ctrl+Up" was sent properly through the VNC client and worked on tmux again.